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2327 lines
105 KiB
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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 102, NO. B8, PAGES 18,179-18,201, AUGUST 10, 1997
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The German Continental Deep Drilling Program KTB:
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Overview and major results
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Rolf EmmermannandJ6mLauterjung
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GeoForschungsZentPruomtsdamP,otsdamG, ermany
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Abstract.The GermanContinentaDl eepDrilling Program(KTB) wasdesignedto studythe propertiesandprocesseosf thedeepercontinentaclrustby meansof a superdeepboreholeM. ajor researchthemeswere(1) thenatureof geophysicasl tructuresandphenomena(,2) thecrustal stressfield andthe brittle-ductiletransition,(3) the thermalstructureof the crust,(4) crustal fluidsandtransportprocessesa,nd(5) structureandevolutionof thecentralEuropeanVariscan basementT. he projectwasconductedin distinctphasesa: preparatoryphase(1982-1984),a phaseof siteselection(1985-1986), anda pilot phase(1987-1990), whichincluded sinkingof a pilotboreholeto 4000 m anda 1-yearexperimentatiopnrogramT. he mainphase(1990-1994) compriseddrillingof a superdeepboreholewhichreacheda final depthof 9101 m anda temperatureof ~265øC,andthreesubsequenltarge-scaleexperimentsin theuncased-bottomhole sectionA. mongtheoutstandingresultsarethefollowing(1) A continuousprofileof the completestresstensorwasobtained.(2) Severallinesof evidenceindicatethatKTB reachedthe present-daybrittle-ductiletransition(.3) The drilledcrustalsegmenits distinguishedby large amountsof freefluidsdownto midcrustalevels.(4) The roleof postorogenibcrittledeformation hadbeengrosslyunderestimated(5.) Steep-angleseismicreflectionsurveysdepictthe deformationpatternof theuppercrust.(6) High-resolutionseismicimagesof thecrustcanbe obtainedwith a newlydevelopedtechniqueof true-amplitudep,restackdepthmigration.(7) The electricalbehaviorof thecrustis determinedby secondarygraphite(+sulfides)in shearzones.
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Introduction
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requireclosecooperationbetweengeoscientistasndengineers,a
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prerequisitewhichdevelopedintoa fruitful symbiosisL. ike any
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In October1994, after 1468daysof drilling, the superdeep expedition to uncharted regions, the KTB project was
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boreholeof the GermanContinentaDl eep Drilling Program meticulouslyplannedto foreseeand minimizepotentialrisks.
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KTB (KontinentalesTiefbohrprogrammder Bundesrepublik Thusthe projectproceededin distinctphasesa, fter eachof
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Deutschlandr)eacheditsfinaldepthof 9101 m at a temperature whicha fundamenttaelevaluatiownasmadeandstrategiewsere
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of ~265øC. The main phaseof the KTB was then concluded redefinedA.ftera preparatorpyhase(1982-1984a) nda phaseof
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with threemajorexperimentsin the uncasedbottomsectionof presiteinvestigationasndsiteselection(1985-1986),the KTB
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the hole: a dipole-dipoleexperiment,a draw-downtestand a pilotphasebeganin 1987.Thisinvolvedsinkinga pilotholeto
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combinedhydrofracturinagndfluid injectionexperimentW. ith 4000m (the"VorbohrungK"T, B-VB)anda subseque1n-tyear this climax to the scientificprogram,the main phaseof the logging,testingand experimentatiopnrogram(until April
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KTB was terminated as scheduledon December 31, 1994.
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1990).The resultsof thepilot phasehada majorimpacton
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The KTB was the largest and most expensiveresearch scientificand technicalplanningof the superdeephole
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programin the geoscienceesver undertakenin Germany.The CHauptbohrung"K, TB-HB), and providedthe basisfor the Federal Ministry for Researchand Technologycommitteda officialgo-aheafdorthemainphaseA. pprovawl asgiventothe
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total of 528 million DM (~$350,000,000U.S.) to the project, designand constructioonf a specializeddrill rig with a
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fromtheplanningphasein 1982throughto completionin 1994. maximumcapacityof 12 km, the targetdepthwassetat the
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A KTB projectgroupe, stablisheadt theGeologicaSlurveyof temperatulreevelof 300øC(expecteadtabout10km),a budget
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LowerSaxony,Hannoverw, asresponsiblfeor thetechnicaal nd wasdetermineda,nd a time framefor the main phasewas
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operational realization of the program. The Deutsche limitedto December31, 1994.The year 1995 wascommitted
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Forschungsgemeinscha(fDt FG) oversaw and coordinatedall for siteshut-dowanndfinaldataevaluationa,ndonJanuary1,
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KTB-relatedscientificactivities.At onetime or anotherduring 1996, the GeoForschungsZentrPumotsdam(GFZ) took over
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this period, more than 700 scientistsand technicianswere responsibilitfyor the final phase.In thisphase,the two drill
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employedin KTB-relatedwork.
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holes,whicharesome200 m apart,will beusedovera 5-year
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KTB fully deservesthe term "superdeepadventure"because periodas a deepcrustallaboratoryfor in situ scientificand
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it advancedthe frontiersof many geoscientificand technical technicalexperiments.
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fields.It wasclearfrom the very beginningthatsuccesswould
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Copyfight1997by theAmericanGeophysicaUl nion
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Papernumber96JB03945. 0148-0227/97/96JB-03945509.00
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Realization of an Idea
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In 1977 the Senate Commission on Geoscientific Research of
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theDeutscheForschungsgemeinschafifrtst discussedtheideaof investigatingthe continentalcrust by meansof a superdeep
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18,179
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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•oo
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EMMERMANN AND LAUTEPOUNG: KTB DEEP DRILL HOLE
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18,180
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE
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18,181
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borehole.At that time, conceptualmodelsof the makeupand Collapse of the Variscan orogen started in the late
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evolution of the continentalcrust were primarily based on Carboniferous(~300 Ma) andwasenhancedby mantle-induced
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interpretationof the geological record, interpretationof crustalextensionand magmaticactivity which heraldedthe
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geophysicalimages obtained from various deep-soundingbreak-upof thenewlyassemblePdangeaT.hisepisodecreateda
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methodsa, ndapplicationof laboratorydatafromexperimental multitudeof Permian(300-250 Ma) bimodal volcanic suites,
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petrologyandgeochemistrtoy realrocks.The commissiofnelt intramontanebasinsandgrabenstructuresm, anyof whichare
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thatfurtherprogressrequired"groundtruth"thatcouldonlybe wrench-relatedD. uringthe Alpine orogeny(~100-30 Ma) the
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obtainedby direct observationthroughdrilling. From the region was affected by compressionaalnd transpressional
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beginningt,hereforet,wo fundamentagl oalsof globalrelevance tectonicswhich were followedby yet anotherstageof rifting
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weresingledout:(1) calibrationof crustalgeophysicsa,nd(2) andgrabenformationin theTertiary(since~25 Ma). Manyof
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studyof thecrustalstressfield andtherheologicablehaviorof theseeventswere accompaniedby magmatismand enhanced
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the crust.In the ensuingyears,discussionws ithin the whole hydrothermaalctivity,causingthe formationof widespread
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geosciencceommunityled to a muchbroadedr efinitionof the mineralization.
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conceptof continentasl uperdeedprilling. In 1984the official This multiply reworkedcentralEuropeancrustis relatively
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proposatlo establishtheKTB wassubmitteadndfive priority thin (~30 km) andextremelyheterogeneousb,oth laterallyand
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areasweredefined:(1) thenatureof geophysicasltructuresand vertically. It is distinguishedby regionally variable but
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phenomenas:eismicreflectorsand electrical,magneticand generally high heat flow values, complex gravimetric and
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gravimetricanomalies;(2) the crustalstressfield and the magnetic patterns, pronounced seismic reflectivity, the
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brittle-ductiletransition:orientationand magnitudeof stresses occurrenceof high-andlow-velocitylayers,andzonesof high
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as a function of depth; (3) the thermal structureof the electricalconductivityat differentdepths.
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continentalcrust: temperaturedistribution,heat flow, heat
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productiona,ndheattransport(;4) crustalfluidsandtransport processesfl:uid systemsf,luid sourcesa,ndfluid movements;Site Selection: A Difficult Decision
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and(5) structureandevolutionof thecentralEuropeanVailscan basement: properties, deformation mechanisms, and geodynamicosf a multiply reactivatedcontinentacl rustal
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environment.
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Altogether,more than 40 potentialdrill siteswere initially suggestedb,utonlyfoursurvivedthefinal definitionof project objectives,and the first main selectionconferencein 1983
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narrowed the choice to two final candidates, the Schwarzwald
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From technicacl onsiderationsa,ndbasedon theexpectation and Oberpfalzregions.As existingknowledgewas inadequate
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of importantchangesin rheologyandreactionkineticsabove to decide betweenthe two, a 2-year programof geological,
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about250øC,the targetwassetat the 250ø-300øCtemperature petrologicala, ndgeophysicasltudieswasstartedin eachregion.
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window. This temperaturetarget was combined with the The results were discussed at a final selection conference in
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objectiveof penetratingat least8000 m into the continental September1986, attendedby over 200 geoscientistosf all
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crust.
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disciplines.
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Fromits inceptionc, losetieswereestablishedbetweenKTB and the German Continental Seismic Reflection Program (DEKORP), whichstartedin 1983 and wasalsofundedby the FederalMinistry for ResearchandTechnology.Together,these projectswereintendedto providea major Germancontribution to understandintghearchitecturec, ompositiona, ndevolutionof
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At thatmeetingit wasacknowledgedthateachregionoffered highly attractive targets for solving a range of pressing geoscientificproblemsand preferencefor one site over the other becamea partisanissueamongthe variousdisciplines. The deadlock was broken by focusing on the expected geothermalgradient.Extrapolationof geothermaldataobtained
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the central Europeancrust. Perhapsbecauseof its relatively young age (typically < 500 Ma), this crustal type differs fundamentallyfrom that sampledby the Russiansuperdeep
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from shallow-drillingstudiescarried out in both regions especiallyfor thispurposeindicatedthatthetargettemperature of 250ø-300øCmight be encounteredat 7 km depth in the
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boreholeKola SG3. Neverthelessc, entralEuropeancrusthasa Schwarzwald,whereasit could lie about 5 km deeperin the
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complexhistory and has been repeatedlyaffectedby major Oberpfalz.Therefore,taking the original depthcriterioninto
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compressionaalndtensionalprocessesIt. waslargelyformedor reshapedduring the Variscan orogeny(~400-300 Ma), which wasan importantsteptowardthe assemblyof Pangea(at ~300
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account,the DeutscheForschungsgemeinschasfetlectedthe Oberpfalz site for the superdeepborehole [Emmermannand Behr, 1987]. The specificscientificattractionsof this site were
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Ma).
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seento be (1) its locationin the suturezone betweentwo first-
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The Variscan belt represents a collage of arcs and microcontinentsresulting from collision of the Old Red Continent(Laurentia+ Baltica + East Avalonia) with Armorica
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order units of the Variscanorogen;(2) the existenceof an appealingand testablegeologicmodelwhich had far-reaching
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implicationsfor crustalarchitectureand geodynamics(;3) the
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and Gondwana.An important rifting phasein Cambrian and Ordoviciantimes(~500 Ma) first separatedthe microplatesof
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East Avalonia and Armorica from mainland Gondwana and
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occurrenceof marked gravity, magnetic,and electrical selfpotential anomalies; (4) the expected presenceof seismic
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reflectors at drillable depths and of an electrical high-
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createdlargeareasof thinnedcontinentalor evenoceaniccrust. conductivitzyoneat 10 __1 km; and(5) thechanceto testfor
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The crustalblocksinvolved beganto convergein Ordovician thermal and geochemicalinfluencesfrom the nearbyTertiary
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time (by ~450 Ma) and were finally weldedtogetherduring a Eger rift.
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prolongedstageof collisionin the Devonianand Carboniferous
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(400-300 Ma) to form thepresent-dayVariscides.Incorporation
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of magmaticarcs and back arc basins,long-distancenappe Two-Step Drilling Concept
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transport, a final stage of low-pressure,high-temperature
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metamorphism, and voluminous intrusion of late to Sincethegeologicabl oundaryconditionsandtheirimpacton
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postorogenigcraniteshavedonemuchto obscurethe recordof the technicalrequirementfsor reachingthe envisageddepth
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oceansopeningandclosing.
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targetwerenotknownsufficientlyt,heKTB conceptwasbased
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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18,182
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EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE
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on drilling two holes,first a pilot hole as a sortof "fact-finding about1.5wt % DEHYDRIL-HT,a synthetich,ectoritc-typLei,-
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mission"andthenthesuperdeepholeitself.
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bearingNa-Mg silicatewhichyieldeda thixotropics, olid-free,
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Main objectives of the pilot phase were to acquire a highly lubricantmud system.Later, due to its electrolyte
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comprehensive set of geoscientific data from core sensitivityc,orrosivebehaviori,nstabilityat hightemperatures,
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investigations,cuttingsanalyses,and boreholemeasurements and other factors,it was continuouslmy odifiedby adding
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with which to develop the methodologyrequiredfor optimal HOSTADRILLa, norganicpolymera,ndNaOHplusNa•CO•to
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evaluation of the superdeephole and to test the geological fix a pH valueof 10 to 11. With increasingtemperaturien the
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prognosesM. oreover, the pilot hole would reducethe needfor deeperpartsof the KTB-HB (below7100 m) and owingto
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samplingand loggingin the upper,largecalibersectionof the continuingsmallinfluxesof salineformationwaters,a steady
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superdeephole and would provide the information on rock deteriorationin rheologicalpropertiesand water-binding
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propertiesanddrillability, boreholestability,potentialgain and capacityrequireda partialreplacemenbty addinga mixtureof
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loss zones,temperatureprofile, etc., critically neededfor the different commercial polymers (KEMSEAL, MILTEMP,
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technicalplanning.
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PYROTROL). Furthermore, in order to reduce borehole
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The KTB pilot hole was spuddedon September27, 1987. instabilitietshemudweightwasraisedfrom 1.06kg/L to 1.40
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The conceptdevelopedby the KTB engineers,which was to kg/L by addingbarite(seeTable 1 for a summaryof fluid
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modify a conventionadl rill rig from industryand to combine systemsusedat variousstages).
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rotarydrilling andwire line coringtechniquest,urnedout to be After completionof the pilothole,a 1-yearmeasuringand
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very successfulW. ith a high-speedtopdriverotatingsystemand experimentationprogram was conducted,which included a
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using an internal and externalflush-jointed5 V2inch mining comprehensiveloggingprogram,14 hydrofracmeasurements
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drill stringwith 6 inch thin-kerfeddiamondcorebits,560 days and a large-scalethree-dimensiona(l3D) seismic reflection
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of drilling and logging were needed to achieve a basement survey,coveringan areaof 19 x 19 km aroundthe drill site. In
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penetrationof 4000 m, and a total of 3564 m of excellent April 1990 the hole was caseddownto 3850 m, leavingan
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quality cores was recovered.By applying straight vertical openholesectionof 150m. Thepilotphasewasthencompleted drillingcapabilitiesthistechniquehasa depthpotentialof 5 to 6 with a first short-termpumptest,whichyielded71 m3 of
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km andthusmaybe of specialimportancefor futurecontinental basemenbtrineswith highamountosf N2 andCH4 fromthe
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researchdrilling to intermediatedepths.
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uncased bottom zone.
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A prerequisitefor the successof the drilling techniquewas The main resultsof the pilot phase[Emrnermann1, 989],
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the developmentof a new water-baseddrilling fluid system, whichdeterminedthetechnicacloncepftor thesuperdeehpole,
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which was undertakenin close cooperationbetween KTB were (1) the considerablyhigher than expectedgeothermal
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engineersand geochemists.This system met all technical gradientw, hichled to a definitionof thedepthtargetat 10 km
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requirementsw, asenvironmentallysafeand,for the first time, (correspondintogabout300øC);(2) thelithologicheterogeneity
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alloweda quantitativegeoscientificmonitoringof the drilled andthecontinuoussteepinclinationof rockunits,whichcaused basementT. he startingcompositionwasa mixtureof waterwith severe deviation of the hole out of the vertical and resulted in
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developmentof a vertical drilling strategy;and (3) the
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frequencyof cataclasticshear zones and fluid inflow zones
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Table 1. Drilling Fluid SystemsUsedin theKTB Main Hole
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which, in combinationwith the high horizontaldifferential stressesl,ed to the expectationthat boreholeinstabilitieswould
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Borehole section
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DrillingFluid System
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Properties
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becomea major problemat depth.This resultedin a slimclearancecasing strategyand developmentof water-based, high-temperaturderillingmudsystemdsescribedabove.
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0 - 6760m
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0.7%Dehydril plasticviscosity9-22mPas
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(1,sidetrack) 1%Hostadrill densit1y.06g/cm3
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Plate 1 showsthe drill rig of the superdeepboreholeKTBHB, UTB 1, which,at a totalheightof 83 m, is thelargestland-
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NaOH, NarCO, pH 10-11
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baseddrill rig in theworld.The rig is fully electricallydriven,
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6460- 7220 m (2, correction)
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1.5% Dehydril 1.5% Hostadrill
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NaOH, Barite
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plasticviscosity29-53 mPas
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density1.06g/cm3
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pH 11
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and incorporatesa number of technical innovations and improvementisncluding,for example,an automaticpipehandling system and remotely controlled gear-driven
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drawworks.
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7140 - 8330 m (2, sidetrack)
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Bentonitc
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plasticviscosity35-91 mPas
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KemseaMl,iltemp, density1.25g/cm•
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Pyrotrol,NaOH pH 10
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Barite
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To ensuresufficientreservest,he drill stringlayout was madefor a maximumdepthof 12,000m (diameterof 5 •Ainch, enhancedsteelquality).By using40 m standsof drill pipe
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insteadof the standard27 m stands,and in combinationwith the
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7460 - 8730 m
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(3, sidetrack)
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Bentonite
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plasticviscosity25-90 mPas
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KemseaMl,iltemp, densit1y.40g/cm•
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Pyrotrol,NaOH pH 9-10
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Barite
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pipe-handlingsystem,roundtriptime was reducedby about 30%. In orderto achievethe targeteddeptha verticaldrilling system(VDS) was developedand deployed.The VDS is an actively self-steeringsystem mounteddirectly above the
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8630 - 9100 m Bentonitc
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plasticviscosity27-59mPas
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KemseaMl,iltemp, densit1y.40g/cm•
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downholemotor.It effectivelyminimizedthe frictionbetween drill stringand boreholewall and allowed a 50% reductionof
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Pyrotrol,NaOH pH 9-10 Barite,Polyglycol
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the drilled rock volume by realizationof the slim-clearance casingconcept.
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The VDS systemwas usedto a depth of 7500 m at the
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All drillingfluid systemsare water-basedD.ehydrilis a synthetic clay mineral (Hectoritc-type)H. ostadrill,Kemseal,Milltemp and
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maximumallowabletemperatureof
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175øCfor
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the electronics,
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Pyrotrolare syntheticviscosifiersand organicadditives.NaOH and whosedata were pulsedthroughthe mud to the surface.The
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Na:CO3 havebeenaddedto controlthepH value.Baritecontrolsthe horizontaldisplacemenatt this depthwas only 12 m, which
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density.
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meantthatthe boreholewaspracticallyvertical.The hole then
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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EMMERMANN AND LAUTERJUNG' KTB DEEP DRILL HOLE
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18,183
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1. Correction for Deviation 1000 rn 1300 rn
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2. Correction for Deviation 1800 rn 2000 m
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3. Correction for Deviation 2600 m 2700 m
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track I 1710rnI
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199m8 I
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2.Side
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track 3767m
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,.,389m3
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- 0 1000 2000 3000
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-4000
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VB
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HB
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Paragne•sses Metabasites VariegaSteedquences
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Major Faults
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1. Correction for Deviation 5530 m 5600 rn
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13518I"
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2. Correction for Deviation 7140 m 7220 m
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1.Side
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track I •o m I
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track 7460m I
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m,I
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track I 8630m
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,, 8730m
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10000
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Figure1. Anoutlineof thefinalboreholceonfiguratiosnh,owintghesidetracksandcorrectionfosrdeviation, casingschemaendlithologicaplrofileof(left)thepilotholaend(right)thesuperdeehpole.
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deviatedtowardtheNE, almostperpendiculatro thegeneraldip boreholeenlargementsp, referentiallyrelatedto shearzones. of the foliation, andat 9069 m, wherethe final deviationsurvey Below that depth,boreholeconvergence(i.e., reductionof the
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was conducted,it showeda horizontaldisplacemenot f about boreholediameter)first occurredand resultedin undergauge 300 m. Down to a depthof 8120 m the superdeephole was hole sectionsU. ndergaugesectionsw, ith uniaxialnarrowingin drilledalmostexclusivelywith downholemotors,whichcould the direction of the maximum horizontal stress, developed be usedto maximumoperatingtemperatureosf about190øC. within hoursandbecamethe major sourceof drilling problems Thelaststeptothefinaldepthwasdonewithrotarydrilling. [Bormet aL, this issue].The drill stringfrequentlygot stuck,
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As coringis oneof the mostexpensivedrillingoperations,and side-trackingoperationsconsumedover 1 year of total maximizingcore recoveryand core qualitywas of special operationtime.Thistypeof instabilityw, hichcauseda creepimportanceT.he experiencewith thethin-kerfeddiamondcore like structuraldisintegrationin the rock, resultedfrom the bits in the pilot hole justified the decisionto adapt this extremely unfavourablecombinationof high differential technologyto the superdeephole. A large diametercoring stressesa,preferreddip of planesof weaknesisn thedirection system(LDCS) wasdevelopedwhich,in the 12 •Ainchphase, of the minimumhorizontalstresscomponent,he presenceof cutcoresof 234 mm diameterandprovidedrockcolumnswith formationwatersandtheelevatedtemperaturesT.he instability a lengthof up to 5 m. In comparisotno rollerco.necorebits, eventuallyformed a technicalbarrier which could not be which were also used,the averagecore recoverywith this overcomewithinthestrictlimitationsof budgetandtime.It was systemwasincreasedfrom41% to about80%. Altogether3, 5 thereforedecidedto stopthedrillingoperationisn October1994 corerunswereperformedin thesuperdeehpolewithanoverall at a depthof 9101m anda temperaturoef ~265øCin orderto recoveryof 84 m. A large additionacl ollectionof partly usethedrillrigandtheothertechnicaflacilitiesforthreelargeorientedrockfragmentsu,pto 10cmin lengthw, asprovidedby scalescientificexperimentsin the uncasedopen-holebottom a junk basket,a simple,but very effectivetool attachedabove section. thedrill bit whichwasalwaysusedin noncoredsections.
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Figure1 showsthe KTB-HB in its final conditionwith the Realizationof the ScientificProgram differentsidetracksandthecasingschemeR. easonsfor theside tracks were corrections for deviation, unsuccessfulfishing The scientific program of KTB was carried out by an operationsa,ndboreholeinstabilitiesD. own to about7500 m integratedevaluationandjoint interpretationof dataandresults theseinstabilitiesmainlyoccurredin theformof breakoutsand obtainedfrom threesources'(1) the field laboratoryestablished drilling-inducedtensile fractures that producedlocalized at the drill site, (2) boreholemeasurementsand experiments,
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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18,184
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EMMERMANANNDLAUTERJUNKGT:BDEEPDRILLHOLE
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and (3) individual specializedresearchprojectscarriedout at
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universities and other research institutions. All KTB-related scientific activities were coordinated and
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Field Laboratory
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reviewed by the DeutscheForschungsgemeinscha(DfiFG), whichestablisheda PriorityProgram"KTB" thatwasfundedat an annuallevel of ~7 million DM. During the lifetime of the KTB, from 1982 to 1995, the DFG administereda total of 75
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million DM (~$ 50 million US) to over 300 different research projectsinvolvingabout500 scientistsI.n addition,some 100 foreignscientistsfrom 11 countriesparticipatedin KTB with a total of 70 researchprojectsfinancedby their nationalfunding agencies.Scientific communicationwithin the DFG Priority Program,periodicdiscussionof the resultsand definition of major experimentswere ensuredby workshops,task group
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Fluids
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Solids
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Gases
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Drillingfluid Fluidsampler
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,,
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Cores Cuttings
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Rock flour
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i • ,
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Gas trap Sampler
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,
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I I
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Petrology and Structure
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Petrography
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Macrostructures
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Ore microscopy Microstructures
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Texture
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C ore ode ntation
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Borehole
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measurements
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meetings,thematicsessionsa, nd the annualKTB colloquium. As of 1995 a total of over2000 publicationshavecomeout of the variousresearchprojects.
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Establishmenot f a field laboratoryat thedrill sitewasa top priority from the time of the first discussionsabout a continental deep drilling program in Germany. The field laboratory became an indispensible component for the realization of the ambitious scientific program. Figure 2 summarizes the tasks of the field laboratory and its organizationalstructure.This lab, which was a modernand completelyequippedresearchinstitute,was supportedby nine university "mother institutes" (under the guidance of the Instituteof GeosciencesU, niversityof Giessen),andstaffedby up to 20 scientistsand 18 techniciansI.ts primarypurposewas
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Petrophysics Density,Porosityand Permeability, Electricand magneticproperties, Soundvelocities,Heat conductivity, y-spectroscopyS, tressrelaxation
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,
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Geochemistry Chemical& mineralogicaclomposition
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of rocks;Fluid-and Gasanalysis
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KTB-Database
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Storage
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Documentation
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Correlations Modelling
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to collect extensivegeoscientificdata on cores,cuttings,rock
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flour, drilling fluidsandgases.Propertiesandcharacteristic(s1) weremeasuredwhichwerenecessaryfor operationadl ecisions
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ISpaamrt•pi_eUl•is[nngiv-ersKitTieBs- concerningdrilling, sampling, and testing, (2) had to be
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determinedon a quasi-continuoubsasisas a functionof depth,
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Reports
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(3) aretime-dependenatndthereforehadto be recordedassoon
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as possibleafter sampling,and (4) were neededfor calibration of boreholemeasurementsand were requiredto guide sample
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Figure2. A flow chartshowingthe samplingandanalysis
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schemeof the KTB field laboratory.
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selection and as basic information for all individual research
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projects.
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Apart from establishedmethodsa, numberof new techniques influxes could be identified and localized,facilitating quick
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were developedand continuouslyimproved.Among them were operationadlecisionsconcerningpositioningof drill stemtests
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a computerizedreorientationtechniquefor cores,a new tool for anddownholefluid sampling.
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high-qualitydensityimagingof coresby gammaray absorption Togetherwith the work in the field laboratoryd, ownhole
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and a four-componendt ilatometerfor the measuremenot f the measurementpslayeda centralrole in thereconstructioonf the
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stressrelaxion of cores. Becauseof the new drilling fluid drilledbasementandprovidedimportantinformationon the in
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systemand a speciallydesignedautomaticsamplingsystem,a situ propertiesof the rocks.Prior to KTB therewas little
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real break-throughwas achievedin the evaluationof cuttings, experiencein the integratedinterpretationof loggingdata
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rock flour, drilling fluid, and gasesdissolvedin the drilling obtainedfrom crystalline rocks [Pechnig et al., this issue].
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fluid. The quantitativechemicaland mineralogicacl omposition Thereforean extensiveloggingtestprogramwasconductedin
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of cuttings and rock flour was determined using a newly thepilotholeusingall availabletypesof tools,andtheborehole
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developed combination of X ray fluorescenceand X ray log responseswere calibratedagainstcore, cuttingsand other
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diffraction, which allowed a reliable reconstruction of the dataprovidedby thefield laboratory.
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drilled basementwithin 1 hourafter sampling[Emrnermannand During the drilling phaseof the pilot hole, sevenlogging
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Lauterjung, 1990]. Because the pilot hole was almost campaignswereperformedat variousintervals,mainlyfor data
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completelycored,it was possibleto comparethe lithological acquisitionand technical purposes.After completionof the
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profile obtained from direct study of cores with that hole,24 differentexperimentswereconducteda,nda totalof 55
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reconstructedfrom cuttings and rock flour analyses.It was toolsweredeployed.On thebasisof theresultsandexperiences
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demonstratedthat the agreeementwas excellent and that every from thesemeasurementst,he combinationof loggingtoolsfor
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rock type, even minor lithologicalchanges,fault zones, and the KTB superdeephole was defined and, altogether,266
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alteredintervals,hadbeenunequivocallyidentified.
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logging runs were performed. Although there were some
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In addition,quasi-onlineanalysesof the drilling fluid, and standard high-temperaturelogging tools available from
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the gasesreleasedfrom drilling fluid, were performed.These industry, several tools were upgradedespeciallyfor KTB.
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fluid logs turned out to be very sensitive indicators of Among thesewas a high-temperatureformationmicroscanner
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cataclastic shear zones and fluid inflow zones. Even minor fluid (FMS) whichcouldbe usedup to 260øC.Figure3 presentsan
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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EMMERMANNANDLAUTERJUNGK:TBDEEPDRILLHOLE
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18,185
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[
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KTB-Oberpfalz HB
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VMG..LS•.TV.•-_R_.••oBH•TV
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14.02.9515:17 / KTB-GP-BM Kiick
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Figur3e. Summoarftyhemajolorggintogolasndtheirrespecmtiveeasurinintegrvinatlhesuperdheoelpe.
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AbbreviatiaorneNsGSn, aturgalammsapectroscDoLpLy;,electricraelsistivistyo;nics,eismvicelocitBy;GT,
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borehgoeleomeTtrEyM' Pte, mperaltougrM'e AGm, agnetomGeLtTeg,r;eochemloicgaglintogolS; Ps, elf potentIiPal,'inductilong;FMS/FMfoI,rmatimonicroscanner/fmorimcraotiimonaBgHeTr;Vb,orehole
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televieweBr;HGM,borehogleravimeteVrS; P,verticasleismipcrofiling.
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overviewof themajortoolsdeployedandthemeasureddepth Apartfromarchivingth, emaintaskof dataprocessinwgas
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sections.
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tointegrataelldataintoa singlea, ccessibilneformatiosnystem,
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A newandveryprecisemethodof lithologiecvaluatioonf which was achievedusingthe metadataconcept.Metadata
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loggingdatawithmultivariatsetatisticwsasdevelopebdy the characterize data sets and include information on data sources
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use of a broadspectrumof Schlumbergetor ols and the andstructuree,xperimentabloundarcyonditionse,xperimental
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comparisoandcalibratiownithcorec, uttingsa,ndmudsample methodsl,iteraturea, nd,mostimportantt,heactuallocationof
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data. This method, which relies on discriminationof thedatasets.The metadataconcepits a basicrequiremenfot r
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"electrofaciesis"d, iscussebdyPechnigetal. [thisissue]a, ndit therealizationof an integratedd,istributedatabasewhichcan
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contributegdreatlytotherefinemenotf thelithologipcrofileof beaccessebdy anycomputenr etwork.
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thesuperdeepborehole.
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The KTB database "KTBase" is a relational database: that is,
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it contains material such as tables of measured data and
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The Information SystemKTBase'.
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observationadlescription(se.g.,thin sectionpetrographyf)rom
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Access to KTB Data
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thefield laboratoryt,hedownholelogginggroup,andthemud
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KTBhasproduceadnenormouasmounotf dataof variouslogginggroupw, hicharestoredseparatealyndcanberetrieved
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kinds(descriptivveersusquantitativneumericadlata)from andconnecteidn anywayby theuser.KTBaseis embeddeidn
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differentsourcesi,ncludingthe field laboratoryb, orehole anapplicatiolnayercomprisinignterfacefsor thepresentation
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measuremenmtsu,dloggingt,echnicaml onitoringe, ophysicaal ndapplicatioonf KTBdataindifferenwt aysT. heapplications
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experimentfsie,ld investigationans,d externasl cientificcover administration tasks, telecommunication facilities,
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investigations.
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databasemanagementa, nd software modulesdeveloped
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
|
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18,186
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EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE
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especiallyfor the scientific technicaltreatmentof data from The metabasicunits comprisecoarse-and fine-grained
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drilling projects,includingnumericaland graphicalsoftware garnet-bearingamphibolites(plagioclaseh, ornblendeg, arnet
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packages. KTBase is now available at the andilmenite),massivemetagabbrowsithrelictophitictextures,
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GeoForschungsZentruPmotsdam.A hypertextlink is installed and thin layers (up to 6 m thick) of mafic and ultramafic
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on the home pageof the GFZ WWW server(http://www.gfz- metacumulaterocks. Most rock types display chemical
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potsdam.de).
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characteristicosf enrichedmid-oceanridge basalts(MORB);
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however, normal MORB compositionsalso occur. These
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Scientific Results
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metabasicunitsperhapsrepresenst licesof formeroceanfloor formedin a backarcenvironmenotr RedSeatypeoceanic
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Crustal Structure and Evolution
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basin.
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The variegatedseriesconsistsof an alternationof massive
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The Oberpfalzis situatedat the westernmargin of the garnetamphibolitesf,ine-grainedbandedamphibolitews ith
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BohemianMassif, the largestcoherentsurfaceexposureof layersof calcsilicataensdmarblesh,ornblende-biogtinteisses, basemenrtocksin centralEuropea, ndit encompasspeasrtsof and paragneissesA.mongthe metabasicrocks,alkali basaltic
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threefirst-ordertectonometamorphuicnitsof theVariscanfold compositionspredominatewith gradual transitionsinto
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belt: the Saxothuringianth, e Moldanubiana, nd the Tepla- trachyandesiticrocks (hornblendegneisses).These units
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Barrandian(Plate 2). This basemenbt lock is separatedfrom constitutea metamorphosevdolcano-sedimentasrysociation
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Pertoo-Mesozoifcorelandsediments(up to 3000 m thick)by with volcaniclastimc aterial,thin lava flows, and pelites the FranconianLineament(FL), a NW-SE trending,deep- interbeddedwith minor marls and limestones.The combination reachingandmultiplyreactivatedsystemof reversefaults.The of turbiditic material with volcanicsand limestoneindicatesa KTB locationis about4 km eastof theFL andjust southof the marinedepositioneanl vironmeinnta tectonicalalyctivesetting.
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boundarybetweenthe Saxothuringianand Moldanubianunits. All threeof theselithologicunitshavesuffereda pervasive
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This boundaryhasbeenregardedas a suturezoneformedby Barrovian-typme etamorphismat upperamphibolitefacies
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closureof an early Paleozoicoceanbasinduringthe Variscan conditions(6-8 kbar and 720øC at peak conditionsin the
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collisionin Devonian/Carboniferotuims es(~400-330Ma).
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paragneisses)c, onnectedwith an intense ductile deformation
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The drill site was located in a small, isolated thatproduceadpenetrativfeoliationW. hereatsheparagneisses
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tectonometamorphiucnit called the ZEV (Zone of Erbendorf- seem to recordprogrademetamorphicevolutionalong the
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Vohenstrau13w),hich representsa variegatedassociationof sillimanite-kyanbitoeundaraynddo not showanysignsof
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paragneisseasndorthogneisseasndmetabasicrockswith minor earlierhigh-pressurevents,the metabasicrockscontainrelics
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metapegmatitesA.ccordingto the resultsof presitestudiesi,n whichclearlydisplaya multistageevolutionfroman early particular lithologic-metamorphiccomparisonswith the high-pressumreetamorphismundereclogitefaciesconditions
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MiJnchbeMrgassiifnthenorthandpreliminairnyterpretatioofn (P> 14kbarT, > ~700øCf)ollowebdyagarnegtranulitfeacies
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conventionallymigratedDEKORP seismicprofiles,the ZEV overprint(P=10-13kbar,T=620-720øCp) riorto thedominant
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had been interpretedas a fiat, bowl-shapedremnantof a amphibolitfeaciesmetamorphism[O'Brienetal., thisissue].
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supracrustal nappe complex straddling the New age determinationsusing a broad spectrumof
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Saxothuringian/Moldanubiabnoundary. In targeting the geochronologmicethodcsonfirmthatthepreVariscaanndearly
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superdeepborehole,it was thereforeexpectedto penetrate Variscanhistoryof the ZEV is muchmore complexthan
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througha 3-5 km thick nappecomplexand to drill into the previousltyhoughatndis distinguishebdyat leastwoseparate
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postulatedsuturezone beneathit.
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metamorphiccycles[O'Brienet al., this issue].The formation
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In fact,howevert,heKTB-HBencounteresdteeplyinclined agesof the metabasicrocksare about485 Ma and nearly
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unitsbelongingto theZEV overtheentiredrilledsectiona, nd contemporaneowuisththeearlyOrdoviciandepositionagl eof
|
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no evidencesupportingthenappeconcepwt asfound.Figure4 the paragneissprotoliths.The earliestmetamorphicevent
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showsa schematicSW-NE profile throughthe ZEV downto recordedin boththemetabasicrocksandparagneissehsasbeen
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about 10 km which summarizesall availablegeological datedat .•475 Ma, using U/Pb chronologyon zirconand
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information.The drilled crustal segmentconsistsof an monazitea, ndit appearsthat the relict high-pressurmeineral
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alternating sequence of three main lithologic units: paragenesepsreservedin the metagabbrocsanbe attributedto
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paragneissems,etabasiteasnda "variegateds"eriesof gneissesthis Early Ordovician high-pressuremetamorphism.
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and amphibolites.Most rocks show a penetrativefoliation Furthermorteh,edataimplythattherewasonlya veryshort
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whichdipssteeplybetween50øand80øto theSW or NE andis time spanbetweenformationof therocks,theirsubductionto at
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foldedintolarge-scaloepenfoldswithNW-SEtrendingaxes. least40 km, and their subsequenrat pid uplift into shallow
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Theparagneissheasvea ratheruniformcompositioanndare (cool)crustallevels.
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madeup essentiallyof plagioclase(oligoclase)q, uartz,biotite, The second metamorphiccycle, that occurred under
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muscoviteg,arnet,sillimanitea, nd/orkyanite;theycommonly Barrovian conditions,can be bracketedbetween about 405 Ma
|
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contain flakes of graphite. The protolithsof these rocks (U-Pbagesof zirconsandRb-Sr,K-Ar and4øAr?Aar gesof representa turbidite sequenceof graywackesand pelitic muscovitesa)nd375 Ma (Rb-Sragesof muscovitefromshear
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graywackesinterlayeredat a centimeterto meterscalewhich zones,probablydatingthe regionaldeformation)N. umerousKhas preservedits original compositionalfeatures.Former Ar, 4øAr?Arand Rb-Sr dateson mineralsindicatethat the
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graywackesshow an equigranularquartz-feldsparfabric, drilledbasemenstegmenta, fter coolingto 350-300øCin the
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whereapseliticlayersare coarsearndricherin micaand LateDevonia(n-360Ma),stayeidn theuppecrrusat nde, ven
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typicallydisplaya biotiteflasertextureA. ccordintgo their moreimportanrte,mainetdherefora longtimeperiodwithina
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chemiccahl aracteristthicepsrotolithwsereratheirmmatuarend narrowdepthandtemperatuirnetervalO. nlymarginaalnd
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containa significanatmounot f basalticmaterialT.heywere deepepr artsof theZEV wereaffectedby theCarboniferous
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probabldyepositeadtanactivecontinentmalargin.
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deformatioandlow-pressuhreig, h-temperatmureetamorphism
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|
21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
|
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18,187
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EMMERMANNANDLAUTER]UNGK:TBDEEPDRILLHOLE
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i E
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
|
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18,188
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EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE
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$w
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Franconian Lineament
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KTB-HB
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NE
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::::::::: .'
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.w•'••:.''"""•'•"ii':•"'•i'•'•.?- ?•' ..•:•ii.•:".:•
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..:.
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Figure4. SchematiScW-NEprofilethroughtheZEV in thesurroundinogfsthe KTB site(no vertical
|
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exaggerationT)h.e metamorphsicequencoef theZEV hasa polyphasheistoryw, ithearlyhigh-pressure
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metamorphiastmabou4t75Ma,andlaterB, arrovian-tympetamorphiastmabou4t00-375Ma.TheFalkenberg granitet,o theNE, intrudedat about310Ma. To theSW areforelandsedimentasryequenceosf Upper CretaceouTs,riassica, ndPermo-Carboniferoaugses.
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(335-325 Ma) which strongly overprinted the neighboring rocksof the variegatedsequenceandareconnectedwith a local
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basement units.
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greenschist facies retrograde overprint. These faults are
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The first evidencefor a commonhistoryof the ZEV and the displacedby reversefaults of possibleCretaceousage, which
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Moldanubian/Saxothuringiaznonesis the emplacementinto all formed under prehnite-actinolite facies conditions. The
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theseunitsof late Carboniferousgraniteswhichoccurredin two youngeststructuralelementsare steepnormal faults probably
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major "pulses",a late tectonicphaseat 335-325 Ma and a relatedto a phaseof grabenformation(Eger Rift) duringthe
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posttectonicphase at 315-305 Ma. The Falkenberggranite, late Oligocene/Miocene(-25-20 Ma).
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whichborderstheZEV ontheNE, hasanageof 311 _+8 Ma Figure 4 depicts the major faults encounteredby the
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(Figure 4). The intrusionof dikes of aplites, calcalkaline superdeepborehole.The most prominentfault system was
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lamprophyre(sdated by *øAr?Ar at -306 Ma) and penetratedbetween6850 m to 7260 m and consistsof a broad
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monzodioritesw, hichcrosscutthe metamorphircocksdownto bundleof individualfault planes.Fissiontrackdataon sphene
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depthsof about7800 m, is closelyrelatedto the granific indicatethat a vertical displacementof more than 3 km took
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magmatism.
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place along this fault system in Cretaceoustime. A second
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The post-Variscahnistoryof theZEV is distinguishebdy major systemoccursbetween7820 m and7950 m, and vertical
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unexpectedlyintense, polyphasedeformation under brittle displacementtherewasat least500 m. Bothsystemsdip steeply
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condition[sWagneretal., thisissue]M. ajordeformatiopnhases to the NE and can be directly correlatedwith the Franconian
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includeintensereversefaultingduringthelateVariscan(.--300 Lineament at the surface.
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Ma) andCretaceou(s.--130-65Maf)ollowedby normalfaulting Fission track studies on apatite, zircon and sphene,in
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duringthe Neogene(<22 Ma). The mostwidespreadbrittle combination with investigations of the Permo-Mesozoic
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elementsin bothboreholesare graphite-bearinlagte Variscan sedimentaryrecordin the westernforelandof the ZEV, provide
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reversefaults.They occurpreferentiallyin paragneisseasnd a detailed picture of the uplift and cooling history of this
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE
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18,189
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basementblock and indicatethat a rock pile of about 15 km has gaseousinclusionswith admixturesof CH4 and N•, and often
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beenerodedsincetheintrusionof the granites.Major phasesof containinggraphite,formedin connectionwith the late Variscan
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uplift and denudationoccurredduring the late Carboniferous cataclasticdeformation (-300 Ma) and are associatedwith the
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and Permian(> 4000 m), lower Triassic(>1500 m), and during graphite-containinsghearzones.
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the Cretaceous(> 3000 m). All are connectedto prominent 'I-'hedominanttype of fluid inclusionsare highly ........
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stagesof crustalshortening.
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Na(e K, Mg)-CI aqueoussolutionswhoseabundancea, swell as
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A highly unexpectedresult, confirmedby a numberof salinity(upto48 wt % NaCI-CaC•I.•) andCa-contenint,crease
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independenotbservationsis, thelackof anyP-T gradientsdown significantlywith depth. These inclusionsrepresenta young
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to at least8000 m and the uniformityof radiometricages.This (<60 Ma) fluid systemthat probablyinfiltrated in connection
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finding,togetherwith the enormousamountof post-Variscanwith theCretaceousphaseof uplift andfaulting. Subrecentfluid
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uplift andcrustalthickeningr,equiresa processof thrustingand activity is reflectedin low salinity Ca-Na-CI inclusionsonly
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stacking.Henceit appearsthat the superdeephole penetrateda foundin the uppersectionof theborehole.
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pile of steeply inclined thrust slices with the Franconian Secondarymineralsdepositedin faults, veins, and veinlets
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Lineament acting as the frontal ramp. Furthermore,the data documentfluid activity relatedto the brittle deformationof the
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suggestthat the slices were detachedfrom a decollement basementT. heir chemicalcompositionand paragenesems irror
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horizoncoincidingwith the Mesozoicbrittle-ductiletransition the evolution of the respectivehydrothermalsystemsand
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zone.
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constrainthe PT conditionsof eachmajor deformationstage.A
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The geologicstartingmodelprovedto be inaccuratea, ndthe sequencewith decreasingagecanbe establishedfrom actinolite
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newinsightsfrom theKTB resultswill havea strongimpacton throughclinozoisite,epidoteand prehniteto laumontitewhich
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ongoingdiscussionsof the structureand geodynamicsof the reflectsa decreasein temperaturefrom about350øC to 160øC
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CentralEuropeanbasementI.t appearsthattheZEV, becauseof (for laumontite).
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its high-levelcrustalpositionsinceDevoniantimes,has been The ZEV rockscontaina surprisinglylarge amountof free
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shieldedfrom theCarboniferousdeformationandhighheatflow fluids,eitherin the form of hydrocarbon-ric"hdry"gasesor as
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event and thereby preserved important structural and formationwaters.Dry gaseswere only detectedin the gaslogs
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evolutionaryinformationonthepreVariscanandearlyVariscan and couldnot be sampleddirectly.They mainlyconsistof
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history.This historyis characterizebdy a doubleP-T loop,with methane with minor helium and radon and are invariably
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a first, high-pressurleoop as early as Lower Ordovicianand a associatedwith graphitizedfaults. Formationwaterswere first
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secondB, arrovian-typeloopin theDevonianT. he integrationof encounteredat 400 m depth, and they occur very commonly
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these findings into the general geodynamic puzzle of from 3200 m downto thefinal depthin numerousdistinctzones
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reconstructingthe Variscanconsolidationof centralEuropeis of upto severaltensof metersin verticalthicknessB. elow2000
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still a matter for further work. Likewise unexpecteda, nd of m the first salinepeakswere detected,and at 3200 m the first
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considerableconsequencewith respect to geologic models openfissuresand porousalterationzonescontaininghighly
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basedonsurfacemapping,is theintensebrittledeformationand salinefluidswerepenetratedS.ignificanftluidinflow(upto 30
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theenormousamountof thrustfaultingwhichhithertohadbeen m•)occurreadtvarioudsepthlevelsassociatwedithmajofrault
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regardedas impossiblefor an "anorogenic"intraplatesetting, zonesor were stimulatedby draw downtests[Huengeset al.,
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about200 km northof theAlps.
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this issue].
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The most promisingfluid-containingsectionswere studied
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Paleofluids and Recent Fluids
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by in situfluid sampling'andencouragebdy a first successful pumpingtestin the pilot hole,a secondl,ong-termpumping
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Fluidsin the Earth'scrustform oneof the mostimportant experimen(tfromAugustuntilDecember,1991)wasconducted
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topicsof contemporargyeosciencea,ndthe superdeepdrill hole in theopen-holesectionof theKTB-VB.460 m3of brineswith
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offersmanynew andsurprisinginsightsinto fluid processeisn about70 g/L TDS and270 m3 of gaseswerepumpedto the
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the past and at present.One of the surprisesfor interpreting surface and continuouslyanalyzed (the "4000 m fluid").
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metamorphicrocksis that,despitethepolymetamorphihcistory Simultaneousmonitoringof the KTB-HB showedthat fluids of
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of the various metamorphicunits and the strongDevonian thetwo boreholescommunicatedthrougha networkof fractures
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medium-pressureoverprint, the primary oxygen and sulfur whichconnectedtheopen-holesectionof thepilotholewiththe
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isotopicpatternsof the protolithshave been preserved.This intervalbetween3000m and6000m of thesuperdeehpole.
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implies that metamorphismtook place under nearly closed- The composition of the formation waters changed
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systemconditionsat low water/rockratios and was not, as has systematicallywith depth,and the followinggeneralvertical
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oftenbeenpostulateda,ccompaniebdy pervasivefluid flow.
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sequencewas established:(1) an upper zone of normal
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The inventory of paleofluids from the ZEV rocks groundwaterextending down to at least 650 m, (2) an
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encompassegsasesandaqueoussolutionstrappedin nanogram intermediatezone of low-salinity,NaCl-dominatedformation
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quantitiesas fluid inclusionsmainly in quartz [MOller et al., watersdownto about3200m, and(3) ,moderatetloyhighly
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this issue].Severalgenerationsand typesof inclusionscan be salineCa-Na-C1basemenbt rineswitha pronounceidncreasein
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distinguisheadndrelatedto distinctgeodynamipcrocessesT.he salinityandCacontenwt ithdepth.Type2 probablyrepresentas
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oldestfluid generationpreservedprobablyrepresentsgaseous formationwaterwhichis evolvinginto type 3 by water/rock
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remnantsfrom the Devonian metamorphismand consistsof interaction.
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water-freeN2-bearinginclusions(with CH,•or CO2)whichhave Table2 summarizetshemajoranalyticaldataof the"4000m
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the highestdensities(about750 kg/m3).Moderatelysaline fluid"(representativoef types)which,at atmospheripcressure,
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NaC1-KCI-MgCaIq2ueouisnclusion(4s-8wt % NaCI•.),which releasedabout0.8 L/L gasesthai weredissolvedunderin-situ
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areconspicuouselynrichedin theuppersectionof theborehole conditionsT.he gasphaseconsistsof 67.0%N2, 31.6%CH4,
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(above4500 m), representa fluid systemthat accompaniedthe 0.52% He, 0.14% At, and0.04% CO2.Chemicaal ndisotopic
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lateCarboniferougsraniticintrusion(s-330 Ma). CO•-dominant datashowthat nitrogenand methanewerederivedby thermal
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
|
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18,190
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EMMERMANN AND LAUTERJUNG:KTB DEEPDRILL HOLE
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Table 2. The "4000 m Fluid"
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Brine Data
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Element
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Na K
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Li
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Ca
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Mg
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Sr Ba
|
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Mn Zn
|
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Cu
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mg/L
|
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7160 231
|
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2.4
|
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15700
|
|
2.2
|
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244 1.5
|
|
0.13 0.01
|
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0.02
|
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s7Sr/•6Sr 0.7095
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•SO
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-5%o
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•D
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- 10%o
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Ele•nent
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•ng/L
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AI Fe
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SiO2
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CI
|
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Br
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F
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SO4 PO4 HCO,
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TDS
|
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pH Eh
|
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<0.015 0.3
|
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54.0
|
|
44100
|
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417
|
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3.8
|
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307 0.5 45
|
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68260
|
|
8.3(in-situ5.3-5.8) -150 (mY)
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Gas Data
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Element
|
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N, CH,
|
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He Ar
|
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CO,
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vol %
|
|
67.0 31.6
|
|
0.52 0.14
|
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0.04
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•N 3Herlie
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+0.30,60 6x 10'6
|
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decompositioonf organicmaterialof a marinesedimentary 10'• m2,whichareseveroarl derosfmagnituhdieghetrhanthe
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source(paragneissprotoliths).The He.isotopicsignatureis matrixpermeabilitoiefstherockassmeasureindthelaboratory
|
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dominatedby radiogeniccrustalhelium, with lessthan 3% of undersimulateidn situcondition[sHuengeestal., thisissue].
|
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mantle component which probably originates from the Theformatiopnressurdeseterminefodrthebrine-containing
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metabasicrocks[M6ller et al., thisissue].
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zonesat differentintervalsshowa progressiviencreasewith
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The chemical compositionof the 4000 m fluid, and depthto a maximumvalue of 105 MPa for the fluids at 9 km.
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especiallyits Ca dominanceh, igh Sr contentand Br/C1ratio Thegradienot f meanformationpressuries about11 MPa/km
|
|
resemblesthatof otherbasemenbt rines (e.g.,in theCanadian andis nonlinear,probablybecausoef a stepwisiencreasien shield,[seeFrape and Fritz, 1982]). Variouslinesof evidence salinitywithdepthI.nflowbehaviodruringthetestsandother
|
|
suggesthat this brine wasoriginallyrich in NaC1andthat its evidenciendicatetshatthebrine-containiznognesrepresenat highcontentsof Ca andSr werederivedfromexchangewith hydraulicallyopen systemwhich is under hydrostatic
|
|
wallrockfeldsparsat 250øC-300øCT. here are no indicationsof conditions.
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contaminationby recentmeteoricwaters.
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|
Application of several independent chemical
|
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geothermometers suggests that the 4000 m brine has GeophysicalStructuresand Phenomena
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|
experienceda temperatureof about 160øC (equilibrium
|
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|
temperature)a, lthoughits in situ temperatureis only 119øC. Crustalseismicstructure.Calibrationof crustalseismic This fluid probablycame from a deeperlevel (-5500 m, structureandunderstandinogf thenatureof reflectorswasone
|
|
correspondingto 160øC) and was "pumped"by tectonic oftheforemoosbt jectivoesftheKTBprogramTo. achievtehis, processeisntoitspresenpt ositionA. ltogethert,heexistingdata a combinatioonfdifferengteophysiceaxlperimenwtsascarried supportthe contentionof M6ller et al. [this issue] that the outto definethepositionandspatiadl istributioonf reflective precursorfluids of this brine were ultimately derived from elemenatsndtounravethl eirmessabgyedirectlpyrobintgheir (evaporitic)Permo-Mesozoicsedimentsin the westernforeland petrophysiccaolm, positioannadlstructurparlopertieWs.iththis of the ZEV and migratedinto their presentpositionin informationa,ndby comparintghe observeadndmodeled
|
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|
connectionwith Cretaceousuplift and deformationby dynamicwavefield,constrainotsnthedecisivelementosf the
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infiltration along the deep reachingfault systemsof the seismicresponsefunctionwerederived.
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Franconian Lineament.
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|
The KTB drill hole was sitedat the intersectionof two
|
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|
Information on in situ permeabilitiesand hydraulic seismipcrofilesD, EKORP-a4ndKTB8502,wherepresite
|
|
propertiesof the basement,which are critically neededfor investigationhsadindicateadnumbeor f reflectorastaccessible
|
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|
understandingand modelinghydrodynamicprocessesc,ome depths[Harjeset al., thisissue].To obtaina moredetailed
|
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|
from a number of borehole experiments.These include seismicimageof the KTB surroundinags3-D seismic drawdownd, rill stemandinjectiontestsconductedat different experime(nIStO89w) asconductiend1989c, overinagnareaof depthlevelsand two very successfukley experimentsa: drill 19x 19kmcentereodnthedrillsite[Harjesetal.,thisissue]. stem test and a combined fluid injection and hydraulic Analysiosf theresultsfromtheISO89experimenletdto an experimenct,arriedoutin theopen-holbeottomsectionof the interpretivgeeologic-tectonmicodelof the crust,a cross superdeepborehole.The resultsobtainedrevealthe existenceof sections, hownin Figure5. Westof the ZEV blockseismic
|
|
a numberof distinct,hydraulicallyconnectedzonesthat are imagesreflectstructureosf theforelandsedimentasn, dwithin relatedto majorfaultsystemsandextenddowntoat least9 km. thebasementwt,omaingrouposf reflectoarsrepresenOt.ne In situpermeabilitiewsithinthesezonesarebetween10'•7m2and groupis planars, teeplyinclined(steepelementsS,E), and
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
|
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sw
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EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE
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18,191
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8
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o
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e:© ß ©©ee
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eeee©eeeee
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.I
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15
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km Figure 5. Interpretationof the seismicprofile KTB 8502. Reflectingelementscanbe dividedinto two groups: steeplyinclinedreflectors(SE1-SE4)andsubhorizontarleflectors(B, G, andR) The darklyshadedzonebounded by thesubhorizontarleflectorsis the"Erbendorbf ody."
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extendsdownto about10 km. The secondgroupof reflectorsis seismograms.Comparison of these with the measured
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subhorizontalandis "bundled"in thedepthinterval>8.5 to 12 seismogramsshowsa fairly goodagreementO. n theotherhand,
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'km. This latter groupmarksa zoneof high seismicreflectivity syntheticseismogramscalculatedusing seismicimpedance
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which,basedon wide-anglereflectionseismicsi,s immediately valuesderivedfrom compositionadlatameasuredon cuttingsin
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underlaibnya high-velociztyone(V•> 7 km/s)T. hisprominent the field laboratoryyielded only very small amplitudes.This
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mid crustal phenomenon, which combines high seismic resultprovesthat the seismicreflectivityof the SEI is not due
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reflectivity and high P wave velocity, is called the Erbendorf to lithologiccontrastbut is mainly causedby the effectsof
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body(darkshadingonFigure5).
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cataclastic deformation.
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Most of the steeplyinclined reflectorscan be tracedto the Altogether,the geophysicarlesultscombinedwith "ground
|
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surfaceandrelatedto known major fault systemsT. he strongest truth" from the boreholehave shownthat steep-angleseismic
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of these reflectors is the so-called SE1 reflector, which strikes reflectionprofiling, at least in this basementregion, mainly
|
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SE-NW and dips 55ø to the NE, has a considerablelateral depictsthe effects of brittle faulting and imagesthe young
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extent, and crosscutsall lithologic boundaries.It can be deformationpattern of the upper crust. Faulting is also
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correlateddirectly to the FranconianLineamentat the surface obviouslyresponsiblefor a 2-3 km verticaldisplacemenotf the
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andclearlyrepresentsits depthcontinuationT. he SE1 reflector subhorizontalreflectors belonging to the Erbendorf body
|
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was predictedto 'occur between6600 and 7100 m in the (Figure 5). This body may well be a metabasicrelict of a
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borehole,and in fact, the most prominentcataclasticfault paleosubductionzone, or a sliver of dense rock emplaced
|
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bundleof the KTB, consistingof at least four major fault tectonicallyduringthe Variscancollision.It is thereforea key
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planesw, asdrilledin thedepthintervalbetween6850and7260 elementin the geodynamicinterpretationof theentirebasement
|
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m. Calculationssuggesthatthecontrastof seismicimpedance region,butmoreinterpretivework,andperhapsevenadditional
|
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betweenthe wallrocksand the permeable,fluid-bearing,and experimentsw, ill beneededto understandfully its nature.
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mineralizedfaultzonecanproducetheobservedreflectivity.
|
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In thecourseof theinterpretivwe orksummarizeadbovet•he
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On thebasisof thesefindings,a'specialseismicexperiment KTB seismic group developeda promising new processing
|
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was designed whose major goal was to quantitatively methodof true-amplitude,prestackmigrationwhichrepresents understansdeismicreflectorsin the crystallinebasementan importantgeneraladvancein seismicdataprocessingT. his
|
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|
[Harjes et al., this issue].The spatial orientationof the methodis basedon a generaldiffractionconceptinsteadof a
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reflectingelementSE1wasdefinedaspreciselyaspossiblea, nd reflectionconceptandprovidesa quantitativeandgeometrically
|
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thegeometryof theseismicexperimenwt asoptimizedin order correctreconstructioonf thereflectivitydistributionwith depth.
|
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to achievemaximumresolutionT. hentheseismicimpedanceof Plate 3 showsa sectionof the KTB 8502 profile which was
|
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the rock section between 6500 and 7500 m was calculated from reprocessewdith thismethod.Comparisonwith Figure5 shows
|
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borehole measurementsand transformed into synthetic theinterpretivepowerof thenew method.
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
|
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18,192
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EMMERMANN AND LAUTERJUNG:KTB DEEPDRILL HOLE
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Geoelectrics. In the last decade many electromagnetic favorablefreeenergyvalueat therelevantemperature3: CH4q'
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surveysof continentalbasementregionshave revealeddeep- 2FeS+ 2H•SO4 • 3Cq'2FeS:+8H20.
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seatedzonesof highelectricalconductivitywhosenatureis still In summaryt,heresultsobtainedoncoremateriaal ndfrom
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enigmatic.Suggestedcausesof thesefeaturesare the presence various borehole measurements indicate that the basement
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of saline fluids, interconnectedfilms of graphite or sulfide sectiond, espitetheubiquitouosccurrencoef salinebrinesh, as,
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mineralizations,or some combinationof these.The European in generala, relativelyhighelectricresistivitwy hichincreases GeotraverseProject (EGT) proved the existenceand large downwardfrom 103k• m at surfaceto 10•k•m at 9 km depth.
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extent of such layers at midcrustal levels in the central Intermediatediscretezonesof low to very low resistivity(1 to
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EuropeanVariscancrust [ERCEUGTGroup, 1992], and they 100 k• m) are in most casesclearly relatedto graphite-
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were also foundduringKTB site selectionstudiesin both the containingshear zones. Graphite (__+sulfidesth)erefore
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SchwarzwaldandOberpfalzregions.
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determinestheelectricalbehaviorof thiscrustalsegment,andit
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Magnetotelluric surveys and long-period magnetic field appeartshatgeoelectricmalethodcsanimagetectonicprocesses
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variations indicated a zone of high electrical conductivity andcanbe usedto tracepaleoshearzones.
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underlyingthe KTB drill site at about 10 km, which has a Gravimetry and Magnetics.The KTB superdeebporehole
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pronouncedanisotropywith maximumconductivityvaluesin wassitedona strongmagnetiacnomalyandgravityhigh,andit
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theN-S direction.After completionof thesuperdeepboreholea, was expected that borehole geophysicsand laboratory
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large-scaledipole-dipoleexperiment(Plate 4), the first of its measuremenotsf rocksamplesobtainedduringdrillingwould
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kind, wascarriedoutto investigatetheextentandpropertiesof give importantnew insightsinto interpretationof such
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this high-conductivityzone [ELEKTB group, this issue],The anomaliesP. late5 showsa new,high-resolutio3n-D gravity
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resultconfirmedthe expectationthat the boreholereachedthis map of the KTB surroundingswhich portrays the density
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zoneandthat the electrodeat 9065 m depthwasindeedlocated distributionT. he pronouncedgravitylow in theNE corresponds
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within a layer of highconductivityT. he positionof thislayerat to the Falkenberggranite,and the strongpositiveanomaliesat
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9 kin roughlycoincideswith the postulatedbasaldetachment the KTB site are due to metabasicbodies.However,despitea
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horizon which is related to the post-Variscancrustal thrust relativelylargedensitycontrasbt etweenthemajorrocktypesof
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stack.
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the ZEV (paragneisse2s740 kg/m3 and metabasite2s890
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Extensivesufacemeasurementswith a variety of electrical kg/m3)t,heirsteepdips,interlayerinagndcomplexstructure
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methodscarriedout in the KTB surroundingsduringthe presite make lithologic interpretationof the gravity pattern very
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surveyandthepilot phaserevealedtheexistenceof shallowlow difficult. A partialsolutionto thisproblemcanbe achievedby a
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electricalresistivityanomaliesandconfirmedthat the drill site combinationof gravity data with results of geomagnetics
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wascloseto thecentreof an unusuallylargesurfaceanomalyof [Bosumet al., this issue].
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the electric self-potential(about-600 mV) extendingNW-SE. The magnetic data give independentinformation about
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That is, the drill site is situated on a "geobattery"which lithology (inventoryof ferri-magneticminerals)and can also
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probablydrawsits energyfrom redox potentialdifferencesin portray tectonicfeatures,like mineralizedshear zones. The
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the subsurface,with graphite-coatedcataclasticshear zones KTB superdeephole penetratedmany magnetic anomalies,
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actingas electronconductingbridges.The modelpresentedby which have a vertical extent of some meters up to about
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Stoll et al., [1995] providesa generalexplanationof the nature hundredmeters.One of the mostimportantof theseanomalies,
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and source of the observed anomalous electric fields. It is with a strongdecreaseof the magneticfield intensity, occurs
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supportedby downholemeasurementsof the self-potentialand nearthe surface.Below about1200 m the total magneticfield
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the redoxpotentialobtainedfrom speciallydevelopedlogging intensityincreasessystematicallywith depthwith a gradientof
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tools.
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up to 200 nT/km, which is muchhigherthan the undisturbed
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Hence it appearsthat graphiteis of specialimportancein Earth'smagneticfield would produce(about22 nT/km). This
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producingthe observedgeoelectricphenomena.Among the result requiresa magneticbody at depth, the exact nature of
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ZEV rocks, the paragneissescontainprimary graphitewhose which, however, remains unknown.Unfortunately,the deep
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crystallinityindicatestemperaturesof about700øC, in accord section of the superdeep hole was cased before a high-
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with the temperaturesof peak metamorphismT. his graphite temperature modification of the magnetometer tool was
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representsoriginal organic material in the protolithsand is developed.Thereforethe intervalbetween6000 m and 8600 m
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finely dispersedso that it does not contributeto the overall wasonly measuredby a SchlumbergeGr PIT inclinometertool,
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electrical conductivity. More important for electrical whose resolution is about 100 times poorer than the
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conductivityis the secondarygraphite,which is ubiquitousin magnetometertool. Nevertheless, the deep magnetic data
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cataclasticshearzones,whereit is always associatedwith iron obtainedwith this tool documentthat the strongestmagnetic
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sulfides and ohiorite. This graphite often forms a quasi- anomalyencounteredin the boreholeoccursbetween7300 m continuous coating along shear planes and is locally and 7900 m.
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concentratedin millimeter-thick layers which constitutegood Surprisingly,pyrrhotiteturnedout to be the main carrier of
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electrical conductors over hundreds of meters.
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rock magnetismin the drilled sequenceand is responsiblefor
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All the evidencesuggeststhat thisgraphitewasprecipitated mostof the observeddownholemagneticanomalies.Magnetite
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from hydrocarbon-bearinfgluidsat about400øCand2 kbar. A plays only a very subordinaterole and is restrictedto a few
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possiblemodeof formationis describedby the reactionCHn+ distinctintervals.It is particularlyenrichedin somepartsof the
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CO2 • 2C + 2H20. This reactionrequiresa relativelyhigh variegatedseries(marbleandcalcsilicate-bearinagmphibolites)
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activation energy, which could be providedby mechanical, between7320 and 7800 m, where it producesthe magnetic
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tribochemical effects in connection with brittle deformation. anomaly mentioned above, which is about 2 orders of
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Alternatively, since graphiteis intimately associatedwith Fe magnitudehigherthananyof thosegeneratedby pyrrhotite.
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sulfides,a reactioninvolvingmethaneandsulfatein the system The pyrrhotitecontentin paragneisseasndmetabasicrocksis
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C-O-H-Fe-S could also be considered, which has a lower, more very similar and mostly below 1 wt %. Enrichmentsup to
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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18,193
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EMMERMANN AND LAUTERJUNG:KTB DEEPDRILL HOLE
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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18,194
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EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE
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v
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r n ¾I
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Plate 4. Schematicsetupof the dipole-dipoleexperimentcarriedout at the final depthof 9101 m. Electric currentwasinjectedat variabledistancesfrom the drill site on two perpendiculapr rofiles.The electricalfield wasmeasuredby two probesat thebottonsof thesuperdeepholeandthepilot hole.The first resultsconfirmthat thesuperdeepholepenetratedinto thehigh-conductivitylayerpredictedto lie at 10ñ1km (shadedband).
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KTB
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0'-.
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-15--o0• -25.
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-30. SW
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-35 -
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s
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-40 •
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-45 -
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-50 -.
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448O•
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4490
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"•
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/ 5540
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/ 5530
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4500 •
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/ 5520
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/•i/ot4o5e14t•52e00 r•e/•/ sso5o 510
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453O
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549O
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Plate5. Three-dimensiongaral vitymapof theKTB surroundingssh,owingthegravityhighat thedrill site causedby metabasiteosf theZEV, andthepronouncegdravitylowsrelatedto theFalkenbergranite(F) to the
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NE andtheforelandsediments(S) to the SW:
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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EMMERMANNANDLAUTERJUNGK: TBDEEPDRILLHOLE
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18,195
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iii
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ml i
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i i
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iii
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i i
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i
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Dme)•o0t.h............T...emperat.u..r.e..3..0..0...
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•:.'. •
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....
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o
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•.' •
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2000
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--'-'-,•,
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..............
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:'•.\..••.•. _ • . ,
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4000
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..
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....... !
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!
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'' '• • '-"'" ••',t•'•
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.....
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•___'._'._ k ',. •......•........
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'. '. '. 'k',-- T(Gradti2e8nfWkm)
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6000 .,. . ....,.. .., . . .•
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..
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. ., T•mperal:u•e•redi
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, ,
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(cacOlated19•6) , _
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" •'
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•1, • lit••u,•nt
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• ß ; %•
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&/• II
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8000 ................
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• '. "
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---
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•
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ß
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•
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,
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ß
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• Finacl repht9'101m • '. •....m,..•
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'
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•.measu4r8•dhafter
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.....
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•th. elast:gir•:u•...•.ati•
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10000 .........
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• '. '.,..
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Plate 6. Diagramshowingthe predictedandmeasuredtemperatureast depthin the KTB site.The curves outlinedin yellowshowthepredictedthermagl radienftrompresitestudies(with lo and20 envelopesT).his predictiotnurnedouttobemuchtoolow.Thebluelinefromsurfacteo4000m showsthemeasuretdemperature profilein thepilothole.Bottomholetemperature(BsHT)atdifferenst tageosf drillingthesuperdeehpoleare shownbyredsquareasndthesecorrespontdo a constangtradienotf 28 K/km.The temperaturaet finaldepth (red dot) was measured48 hoursafter drilling ceasedT. he red shadedfield showsthe temperatureprofile
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predictedfrom the6000 m BHT andbasedon 31 K/km and28 K/kin.
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
|
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18,196
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EMMERMANNAND LAUTERJUNG:KTB DEEPDRILL HOLE
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severalweight percentare typical for hornblendegneissesand wasalsodesignedw, hichprovideda wealthof newinformation
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all major shear zones. Since it was known from laboratory aboutthe thermalstructureof the drilledsegmenat ndled to
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experiments that pyrrhotite occurs in at least two low- improved methodsof handling downholetemperature
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temperaturepolymorphs, a monoclinic ferrimagnetic and a measurementsT. able 3 presentsa summaryof values for
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hexagonalantiferromagneticmodification,and that the Curie thermalconductivityand heat production.Rock foliationand
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temperatureof this mineral is around 300øC the superdeep microcracksare responsiblefor significantanisotropyin
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borehole offered an ideal opportunity to study the in situ thermalconductivit(yupto 20%), withhighesvt aluesparallel
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magnetomineralogical properties of this hitherto poorly to foliation.The distributionof heatproductionwith depth
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investigatedmineral[Kontnyet al., thisissue].
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reflectslocallithologiesT.he data,in generals, howa slight
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Among the most important results of this study is that decreasbeutdefinitelydo notconfirmthewidelycitedlaw of
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frequently, both monoclinic and hexagonalpyrrhotite occur an exponentiadlecreasoef heatproductionwithdepth(Figure
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together,mostlyin intimateintergrowthsw, ith the monoclinic 6).
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polymorph being dominant in metabasic units. Hexagonal Geothermadlatafromthesuperdeebporeholeareconsistent
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pyrrhotite is the stable phase at higher temperatures(above withtheresultsandpredictionfsromthepilothole.Withinthe
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about 220øC) and it predominates below 8000 m. The upper1500m thetemperaturegradientincreasedfrom 20 K/km
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observations of monoclinic pyrrhotite grains with relict to about 28 K/km at 1500 m and remained at that value down to
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hexagonalcoresindicatelow-temperaturetransformationfrom the final depth.On that basis,the undisturbeedquilibrium
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an originally hexagonal phase during uplift and cooling. temperatureat 9100 m is about265øC.Within uncertaintyt,he
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Accordingto experimentalfindingsthe Curie temperatureof verticalheatflow densityw, hichis theproducot f temperature
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hexagonapl yrrhotitemightbe aslow as260øC.It is well known gradientand vertical thermalconductivityi,s also constant
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from laboratorymeasurementsthat the magneticsusceptibility below 1500 m, with a mean value of around 85 mW/m'.
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increasesstrongly at temperaturesjust below the Curie Estimationof thecontributioonf thecumulativheeatproduction
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temperature(the Hopkinsoneffect), and one of the open rateto theverticalheatflow densityshowsthattheupper6 km
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questionsrelevantto the boreholemagneticstudiesis whether of the penetratedbasemenot nly provideabout10% of the
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the Hopkinsoneffect contributessignificantlyto the observed calculatedheatflowdensityvalueof 85 mW/m'at 1.5km. If
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anomalousdepth gradientin the magneticfield intensity,or this value is typical for the crust, then a shift in the thermal
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whetherthe magnetite-containinlgayer is sufficientto produce gradienttolowervaluesmustoccurwellbelow10kmdepth.
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this phenomenon.
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The results of thermal studies in the two boreholes raise a
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The geopotentialfields, electric, gravity, and magnetic, number of basic questionsabout the heat budgetin the
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provide complementaryinformation. Whereas geoelectrics continentaclrust.Oneof theproblemsis howtoexplainthelow
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mainlyimagetectonicfeaturesandgravityprovideslithological thermalgradientin theuppermost1500m, andhowto reconcile
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information,geomagneticscarry informationaboutboth. The the--25mW/md' eficiitn heatflowdensitbyetweetnheupper
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combined evaluation of data from the three sources, now and lower boreholesectionsT. hree alternativesare currently
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underway, will contribute to a detailed 3-D geologic discussedw, hichmayworkin concert:(1) topography-enhanced
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reconstructionof theKTB surroundings.
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heat advection by groundwater flow; (2) paleoclimatic
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Geothermalstudies.Evaluationof thegeothermadl atafrom perturbationof thesteadystatetemperaturefield dueto changes
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the KTB pilot hole providedthe highly unexpectedresultthat of the meansurfacetemperature(e.g., in connectionwith the
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the thermalgradient(21 K/km) and verticalheat flow density last ice age); and (3) disturbancesof the steady state
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(55mW/m')metthepredictevdaluesonlyintheupper1000m. temperaturefield due to lateral refraction of heat flow in a
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Both parametersthenincreasedrapidly to about 1500 m, after compositionallyandstructurallyvery heterogeneoussubsurface
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which almost constantgradientsof 28 K/km and heat flow [Clauser et al., this issue].
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valuesof 85 mW/m'prevailedT.hetemperatuirne thepilot Modeling of available data prove that both groundwater
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hole at 4000 m was 119øC and lay well above even the upper advectionand paleoclimaticeffects are able to producethe
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error limit calculated from the data obtainedby the shallow- measurednear-surfacethermal gradient and heat flow, but the
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drilling geothermalstudies(Plate 6).
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exactcontributionof eachprocesscannotyet be quantified.In
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The desireto explainthe failed prognosisled to an ambitious any case, the observationsclearly demonstratethat external
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research effort [Clauser et al., this issue]. The KTB field lab factorsinfluencethe near-surfacetemperaturefield in the crust,
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carried out a large numberof measurementson core material and this suggeststhat values of geothermalgradientand heat
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andcuttingsto determinestatisticallysoundvaluesfor thermal flow from shallowdrill holesin crystallineterranestend to be
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conductivity,heatdiffusion,andheatproductionto be usedin systematicallytoolow.
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thermal modeling. An extensivegeothermallogging program Another set of problemsis raised by the surprisinglyhigh
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Table 3. Parameters Used for Geothermal Calculations
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Paragneisses HornblendeGneisses
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ThermalconductivityW, /m K Heatproductionla, W/ms Naturalgammaactivity,c/skg Potassium,wt %
|
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Uranium,ppm Thorium,ppm
|
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1.50+ 0.19 51 ñ 5 3.4 ñ 0.2
|
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2.24 ñ 0.25
|
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2.8 ñ 0.4 7.9 ñ 1.0
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1.15ñ 0.11 39 ñ 5
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2.8 ñ 0.2 1.9 ñ 0.22
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2.0 ñ 0.2 5.7 ñ 0.8
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Amphibolites
|
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0.53 ñ 0.28 23 ñ 7 2.6 ñ 0.2
|
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0.88 ñ 0.42 1.0ñ 0.6 2.5 ñ 1.5
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
|
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|
EMMERMANNANDLAUTERJUNGK' TBDEEPDRILLHOLE
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18,197
|
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|
.
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'""'"•' "':.....
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ß.:..:.•",'. .:•;•'.•......
|
|
ß..'...:.:,.•v..:•,•_..•..•::-•'l,.'.';.-•.:.;.. .....:•œ.-.•.g,-?.2.'.'.,:.:•.
|
|
.: '•. ß .,t.,. ß
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|
at the KTB site well correspondsto the averagebackground
|
|
valueofabou8t 0mW/m2insoutherGnermany.
|
|
Rheology and Stress Field. A key target of the KTB programfrom the very beginningwas the studyof the stateof stressin the Earth'scrustandthe rheologicalbehaviorof rocks
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....
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under_in situ conditions down to mid crustal levels. Current
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understandinogf the rheologyof the continentacl rustis based
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primarily on laboratorystudiesof rock strengthundergreatly
|
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•......'.' .•,•A?•..:.•:.,:•.
|
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|
simplified conditions.These studiesindicate that two major processescontrolthe mechanicalbehaviorof crustalrocks:(1)
|
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"ß• •.. .:,•..•!".'"'
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. ..
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In upper crustallevels, deformationcausesbrittle failure and rock strengthis limited by frictional strengthof preexisting
|
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faults. Becausethe frictional strengthincreaseslinearly with
|
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'?';'tg•;•:-.':.:-.'
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confining pressure,the strengthof the crust correspondingly increaseswith depth. (2) At greater depth, beyond a certain
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.r•: •'.:,.
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temperatureand at low strainrates,rock strengthis determined by flow laws and decreasesexponentiallywith furtherrise in
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temperature.
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......'., .•/,
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ß
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ß
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ß(.'-d:•.-',•...•ß. .
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....;..?..'•a:.v.,.. .
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ß....:: ,
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.•..[.;.,...
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' •:;Z•..:......
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ß ...''....:12.[. :......:... ß ,..
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_
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. . ß-.' ..s.•&-•.::'
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'::'-"'"' ß....•..:;•.-•j¾.:...:.:.
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ß
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The change from brittle to ductile (plastic) behavior, commonlyreferredto as the brittle-ductiletransition,depends on factors such as, among others, rock mineralogy, fluid content, and strain rate. Therefore, in nature a more or less
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broadtransitionzonecanbe expected.Most modelsof rheology are basedon the mechanicalpropertiesof quartzbecauseof its abundancien continentacl rustalrocks.Accordingto the "quartz
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model"(Figure7), thereis a linearbuildupof differentialstress
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with depthin the crustto the brittle-ductiletransitionat about
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300øC,after which rock strength,and thus the magnitudeof
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0.0
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1.0
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2.0
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3.0
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"stored"stressf,allsexponentially. Obviously,thereare shortcomingisn sucha simplemodel.
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HPR [laW/m3]
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Apart from uncertaintiesin the physical-mechanicaplroperties of mineralsandrocks,a morefundamentapl roblemis that the
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Figure 6. Diagram showingthe changesin heat production thresholdtemperaturefor ductileflow is criticallydependenotn
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values,as measuredby laboratoryexperimentsand downhole strainrate,andrealisticstrainrates(10'•ns'• to 10'• s'•) are
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logging, with depth in the superdeepborehole.The commonly unattainablein the laboratory.On diagramslike Figure 7, the
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cited exponentialdecreasein heat productionwith depthis not confirmedby thesedata.Instead,onefindsintervalsof constant
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expectednaturalsituationis thereforedepictedas a continuous
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averageheat production(vertical lines) which correlate with transitionfrom thebrittleto theductileregime.
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lithologicchanges.
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With a basaltemperatureof about265øC,theKTB superdeep
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hole has penetratedinto depthsin which the brittle-ductile
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transitioncan be expected,and thusa uniqueopportunityis
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available to study this fundamentalregion in situ. The most
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valueof 85 mW/m2for theheatflowdensityat 8 kmdepth. importantelementsof thesestudiesare the determinationof the
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Extrapolationof the temperaturegradient measuredin the stresstensorwith depth and the structuralanalysisof rocks
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superdeephole using conventionalmodels for the lower crust fromdepthapproachingthetransitionzone.Fromthebeginning
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and assuming conductive heat flow leads to predicted of the KTB program, geoscientistsand engineers worked
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temperatureswell above800øCand heat flow densitiesof 55 to closely together to develop an integratedstressmeasurement
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80mW/m2at thecrust/mantbleoundariny 30kmdepthT, here strategy that involved a number of different methods and
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is no evidencefor partial meltingat this depthfrom seismic experimentswhosecommongoal was to establisha continuous
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data, and there are also other reasons to expect lower temperaturefsor thecrust/mantleboundaryT. hereforeonemust questionthe model assumptionsI.s there an additionalheat
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source in the crust below the drill site? Could the Erbendorf
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stressprofile from the surfaceto the final depth.Theseinclude modified hydraulic fracturing tests and analysis of borehole breakoutsand drilling-inducedtensile fractures[Brudy et al., this issue].
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bodybe responsiblefor highheatproductionor are thereeven The magnitude of the least horizontal principal stress
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significantheatinputsfrom exothermahl ydrationreactionsin component(S•) was determined by conventionalhydraulic the middle and lower crust?Is the assumptionof conductive fracturing experiments in the pilot hole (14 experiments
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heattransportincorrect,and can fluid convectionrelatedto the between800 m and 3000 m), and by two modified hydraulic
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FranconianLineamentexplainthedilemma?
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fracturing experimentsat 6018 and 9070 m depth in the
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Theseand other ideaswill be explorednumericallyand superdeephole.Theseexperimentsyieldedinprecisevaluesfor
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additionalconstraintsare expectedfrom plannedgeothermal themaximumhorizontasl tresscomponen(tS•t),andthereforea experimentsin the KTB "Deep Crustal Laboratory."The new methodwas developedto estimatethe magnitudeof proposedidea that the thermal anomaly around the Tertiary from a combinedanalysisof boreholebreakoutsand drillingEgerRift, to thenorthof thedrill site,is thecauseof thehigh inducedtensilefracturesof the boreholewall. Assumingthat heatflow densitycanbe discountedbecausethevaluemeasured the vertical stressS,., whose value was calculatedfrom the
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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18,198
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EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE
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differential stress
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,
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',
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criteriom for friction-
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',,,••r ..•" controlslelidding
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\,
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transitionI alß,
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.•. •=10'•e
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range /.•':'•,, "britptleastircansition"
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--300 øC
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,,•,,"
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,, .......
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•= 10-14
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KTB
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/
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-
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depth (z)
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T = f(z) p = f(z)
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flloafwoqwruartzite strainrate• as indicated[s-•]
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(dislocationcreep)
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Figure 7. Schematicdiagramshowingthe dependenceof crustalrheology(basedon the behaviorof quartzite) on pressure(depth)andtemperatureandthe magnitudeof differentialstress[Stoeckhert1, 994]. The final depth of the KTB borehole(9101) reachedthe zoneof transitionalbrittle-ductilebehavior.
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lithology of the drilled sectionand density of the respective hundredsof metersfrom the injectionzonein the depthrange
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rock types,is a principalstresscomponenta, continuousprofile between8 and9 km [ZobackandHarjes, thisissue].
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of the complete stress tensor down to about 9 km was The inducedseismicitywasrecordedby a surfacenetworkof
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established.
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70 stationsandwith a three-componengteophonetooldeployed
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The combined results of all stress measurements indicate that at 4 km depthin thepilot hole.Clusteranalysisshowedthatthe
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thedirectionof S, is remarkablyuniformat N160øE+10ø over events were concentratedat two different depth levels, both almostheentireinvestigateddepthrangefrom3 km to 9 km, abovethe injectionzone and extendingabout 1 km from the
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andit correspondwsell with theN146øEregionalorientationof borehole.Fault planesolutionsof the seismiceventsindicatea S, in centralEuropeT. he only significancthangeof Ss with strike-slipcharacter,andthisdocumentsthatthecrustat 8-9 km
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deptihsa shifot fabou6t0ø,toN220øWat,7200mwhichis stillin a stateof frictioneaql uilibriuHmo.wevetrh,e
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coincidwesiththelowermofasut ltplaneof theSE1fault compleatbesenocfeinduceedarthquankeeas9r 030mdepth,
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bundlVea. lueosfthemagnituodfSe,at6018mand9070m couplwediththeobservatthioatntheseismeivcenctslustering
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depth in the superdeephole are 111 MPa and 183 MPa, at a depthof about8.7 km, indicatesan abruptchangeof the
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respectively,andthe estimateddifferentialstressesare between stressstate,and markedlylower shearstressessuggesthat the
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180 MPa and 147 MPa. Apart from theuppermosst ectionof the bottomof theboreholemay benearthebrittle-ductiletransition.
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drill hole downto about1000 m, whereS. appearsto be the A different approachto identifying directly the current
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leastprincipasl tresst,hestressmagnitudeosbtainedfromS,,Ss
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brittle-ductiletransitionzone comesfrom combiningdata on the presentstateof stresswith the resultsof microscopicand
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andSv(-240 MPa at 9100 m) indicatestrike-slipconditions(S, <S,< S.).
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submicroscopitcexturalstudiesof minerals,especiallyquartz, in the suspectedepthrange[Dresenet al., thisissue].Because
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The datasupporthe hypothesisthatthe stateof stressin the the rate of processeswhich control quartz texturesincreases
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brittle crust is limited by the frictional equilibrium on exponentiallywith increasingtemperaturei,t wasexpectedthat
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preexisftainuglatsndthatthecontineunptaplcerusatctassa significcahnat ngienstexturfaelaturwesouladppeoarn
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stresgsuidaendiscapabolfetransmitftoinrgceosfhundreodf sapproachthinetgransitizoonneT.herefoqrueartfzromcutting
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megapasccaolsm, paratbolethosexertebdy plate-drivisnagmplteaskeqnuasi-continuboeulosw7ly000mwasanalyzed
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processes.
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by opticalmicroscopyandtransmissioenlectronmicroscopyI.n
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The urgentquestionof whetherthe brittle-ductiletransition general,the quartzmicrotexturesare similar within the depth
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wasencountereidn the KTB superdeephole canbe answered interval 7-9 km; however, there are systematicqualitative
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with a definite"maybe."One of the mostimportantlinesof changes with depth. These include an improved spatial
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evidencecomesfrom a large-scalehydraulicfracturingand organizationof dislocationsd, ecreaseof dislocationdensity,
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fluid injectionexperimenct onductedin theuncasedbottomhole and submicroscopifcluid inclusionsand indicatean increasing
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sectionat theconclusioonf drillingandwasespeciallydevoted rate of thermallyactivatedrecoveryprocessesT. hesefindings,
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to testingthe brittle-ductiletransitionhypothesisW. ithin 25 like those of the hydaulic fracturing and fluid injection
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hours2,00m3ofluidwereinjecteidntothecrusat tabou9t030 experiments,indicatethat the superdeephole might have, in
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m and some 400 microearthquakewsere triggereda few fact, reachedthepresent-daybrittle-ductiletransitionzone.
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
|
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|
EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE
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18,199
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Deep Crustal Laboratory: A TelescopeInto the
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Earth's Interior
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levels. This was done using a combinationof hydraulic fracturingtestswithanalyseosf compression(barleakoutsa)nd
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tensilefailures (drilling-inducedfractures)of the borehole
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A detailedpictureof thecrustalsectionandits propertieshas walls.Thestudyhasshownthatthebrittleuppercrustis strong,
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been assembled from the field experiments, laboratory "stress-loadeda,"nd capableof sustainingand transmitting
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investigationsand boreholemeasurementsof the KTB main forcesof plate-drivinmg agnitudeT.hegeneratioonf hundreds
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phase.Duringthenext5 yearsof thefinal phase,supplementary of microearthquakbesy extremelysmall increasein pore
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experimentsare plannedusingthe globally uniqueassociation pressur(e< 1 MPa)indicatetshatstresslevelsthroughouthte
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of two deep boreholesinto the crystalline basementwith a brittlecrustarenearits frictionalstrengthandthatonly a small
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separationof 200 m.
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stressincreaseis necessartyo inducefailure.Thesefindings
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Two main objectives of this so-called "Deep Crustal provethevalidityof experimentaldlyerivedtheoreticasltress
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Laboratory" have been defined: (1) The discrimination of profilesa,ndconfirmthatcrustasltrengtihn situdependosnthe
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geophysicalsignalsgeneratedby deep-seatedprocessesand by frictionasl trengthon preexistingfa, vorablyorientedfractures
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shallow events. Conventionaldeep-soundingmethodscan be with coefficientsof frictionin therangeof 0.6 to 1.0 [Byerlee,
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interfered with by effects induced at the Earth-Atmosphere 1978].
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interfaceand disturbedby structuresand processesat shallow The brittle-ductile transition. The lack of induced
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depth. (2) Determinationof equilibriumvalues of physical microearthquakebselowabout9 km suggesttshatthebottomof
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parametersandtheirlong-periodvariationswithtimeanddepth. thesuperdeepboreholeis closeto thepresent-daybrittle-ductile
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Theseobjectiveswill be tackledby deploymentof instruments transition.This hasbeenconfirmedby detailedstudyof quartz
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at variousdepthandtime intervals.
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microstructureisn gneissesw, herestrainis partitionedbetween
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Altogether,threegeneraltypesof experimentsare planned: brittle fracture, solution/precipitationcreep, and plastic flow.
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(1) Stationary registrationof time-dependentvariations of Measurementsof the dislocation density in quartz, which
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physical parameters at different depths under "natural" decreasestowardthe bottomof the borehole,yield differential
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boundaryconditions:plannedinvestigationsincludelong-term stressesof about 140 MPa, which approximatelyequal the
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measurementosf the seismicity,tidal effects,deformation,and confining pressureat that depth. Thus the emprical Goetze
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naturalelectromagnetiecvents(in addition,depthprofilesof criterion also indicatesthat plastic flow contributesto rock
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equilibriumfield valueswill be registered(e.g., temperature, deformationat final depths[Dresenet al., thisissue].
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heat production)),(2) experimentsu, niqueor repeated,with Crustal fluids and rock permeability. Mixturesof aqueous
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defined changes in boundary conditions (e.g., downhole and gaseousfluids are widespreadin the upper9 km of the
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measurements of seismic surface vibrations and active electrical continental crust sampled by the KTB. Fluids are mostly
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experimentsor hydraulic/fluidtests),(3) cross-holexperiments confined to faults and fractures, and these were encountered,
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(the useof two holesallowsspecificexperimentsto investigate even at bottom hole depths,in numerousdistinct zonesup to
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hydraulicconnectivityandfluid pathwaysaswell asanisotropy severaltensof metersthick. The permeabilityof thesezonesis of physicalparameters(e.g., seismicwave-propagationu)nder of the orderof 10"s to 10'•7m2, which is severalordersof
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naturalconditions)A. particularbenefitof the closeproximity magnitudehigher than the matrix permeability of the rocks.
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of the two deep boreholesis the ability to perform seismic Formationpressuresdeterminedin brine-containingzonesshow
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cross-hole experiments with higher frequencies and thus a nonlinear increase with depth, probably due to stepwise
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improvedspatialresolutionT. his typeof experimentswill close increasesin salinity.The formationpressureof 103 MPa at 9
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the gap in scale factor between laboratory measurements km is near-hydrostaticT. his, and the fact that experiments
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(centimeterrange),boreholemeasurement(sdezimeterrange), proveda hydraulicconnectionbetweenthe pilot hole and the
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seismicfield experiments(kilometerrange) and seismology main hole, indicates that fluid pathways are highly
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(100-1000 km range).
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interconnected.
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Finally,it is plannedto expandintoa 3-D triangulararrayby The compositionof the fluids varies systematicallywith
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sinkinga thirdholedownto about1000m andtherebycreatea depth:groundwaterin the upperlevels,NaCl-dominatedfluids
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greatly improved"telescope"into Earth's interior. With this of low salinityat intermediatedepths,andhighlysaline,Ca-Na-
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configurationthe DeepCrustalLab will providea platformfor C1basemenbt rinesbelowabout3200 m. The lattercontainhigh
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high-resolutioninvestigationsof anisotropyand transport amountsof dissolvedgas (~0.dL/L of brine), mainly nitrogen
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propertiesin thevicinityof thesiteandwill greatlyimprovethe and methane,which is derivedby thermaldecompositioonf
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discriminationbetweendeep-seateadndnear-surfaceeffectsand organicmaterialin the paragneissprotoliths.Data suggesthat
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processes.
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Permo-Triassicevaporitesin the sedimentarybasinwestof the
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drill site are the ultimate source of the brines, which have
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Conclusions
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infiltratedthebasemenatlongdeep-reachinfgaultsystemsdown to at least 10 km depth.
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In this paper we attemptedto summarizethe scientific Graphite and geoelectricanomalies.Despitetheubiquitous
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advancesgainedby the continentaldeep drilling program,the presenceof salinebrines,the electricalresistivityincreasesi,n
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KTB,withrespetcotallofthemajorresearcthhemeSs.omoef generaflr,om103C]matsurfacteo l0sC]mat9 kmdepths.
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theresultws illhaveth6irgreatesimt pacitn advancinreggionalLocal anomalies, at various depths, with extremely low
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studies, whereasothers are of general significance.In this resistivity(1 to 100fi m) areclearlyrelatedto graphite-bearing
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conclusionwe pick out thoseaspectsof the KTB scientific shearzones.Graphitein suchshearzonesis interconnectedover
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programwhichareprincipallyof globalimportanceandwhich distancesof hundredsof meters, and this phenomenon
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couldnot havebeenobtainedwithoutdrilling.
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obviouslydeterminesthe electricalresponseof the basement.
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Stress field. A continuousprofile of the complete stress Before drilling, a prominentlow-resistivitylayer of regional
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tensor has been obtained from the surface down to midcrustal extentwaspostulatedat about10 + 1 km depth.This zonewas
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
|
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|
18,200
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|
EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE
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|
the target of a dipole-dipoleexperimentconductedin the The complexity of the drilled crustalstructuresinspiredthe
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|
boreholeaftercessationof drilling. It turnsout thatthebottom development of a new seismic processingmethod (true
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|
depthof the KTB is well within this majorconductorw, hose amplitude,prestackmigration) and demonstratedthe need to
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|
positioncoincideswith a postulatedbasaldetachmenzt one of consider3-D aspectsin seismicimaging. The new method
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|
the post-Variscanthrusts(Mesozoicbrittle-ductiletransition). providedhigh-resolutioinmagesof themidcrustandlowercrust
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|
An importantimplicationof thesefindingsis that geoelectric at the KTB site. It has been and will continue to be used for
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surveyscouldbeusedto mappaleosheazronesandthushelpin reprocessingand reinterpretationof existing seismic records,
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|
tectonic reconstructions.
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for example, the DEKORP data, and thus holds great promise
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Thermal structureof the crust.A majorlessonof theKTB for newinsightsintothedeepstructureof crystallinebasement.
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is that geothermaldata obtainedfrom shallowwells shouldbe
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usedwith greatcautionin makinggeothermapl rognosesT.he Looking Back thermasl tructuroef theuppermos1t500m of thecrustis highly
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disturbedI.n thisintervalthe geothermagl radientis about21 As this paper goesto press,we look back on 19 yearsof
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K/km and the heat flow reachesvalues of about 55 mW/m2. involvemenitn theKTB programs, tartingin the first planning
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Both parametersthenincreaserapidly to about27.5 K/km and stagesin 1977, to thecessationof drilling in 1994, andon to the
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85mW/m2,respectivealyn,dremainclosetothoselevelsright final phase of on-site experimentationin the Deep Crustal
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responsiblefor the near-surfaceeffects: heat advectionby LaboratoryT. he successof theKTB programdependedonclose
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topographically induced groundwater flow and surface cooperationamong diverse groups including ministries and
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temperaturefluctuationsdue to paleoclimate.The effect of agencies, management teams and engineering units from
|
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paleoclimateis dominant.In particular,the last ice age is industry and academia,and not least the scientists,those
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responsiblefor a perturbationof up to severaldegreesin the assignedto the KTB field laboratoryand scientistsfrom
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present-daytemperaturedistributionof the upper4 km. Below universities and researchinsitutes. It might be useful to
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about2000 m, advectionis negligibleandheattransporct anbe summarize,from ourcurrentperspectivew, hatwe believewere
|
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describedby a purelyconductivemodel.
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the key elementsfor the successof the German Continental
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The KTB has fostereda numberof importantadvancesin Deep Drilling Program and what we would probably do
|
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interpretingand modelingheat flow data. For example,the differentlya secondtime.
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intimatealternationof gneissand metabasiteunitswith near- The singlemostimportantfactorwasthe continuingsupport
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vertical contactswas ideal for studyingthe effects of lateral andparticipationfrom the geosciencecommunityin Germany,
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refractionof heat flow and for developingnew modelswhich both from the professionalsocietiesand steeringcommittees
|
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take theseeffectsinto account.The large amountof datafrom and from the leadingindividualsin most branchesof the solid
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loggingand from laboratorymeasurementcslearly refutedthe earthscienceswhoparticipatedin theprogram.Thisbroadbasis
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widely held assumptionthat heat-producingelements are of supportresultedfrom a long conceptfinding phase,which
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strongly concentratedin the upper crust and then decrease lastednearly7 years,andduringwhichthe fundamentaal spects
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exponentially with depth. Instead, the data show that heat andgeneralphilosophyof thedrilling programwerediscussed.
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productionis controlledby lithology,and thereis only a very The resultof thisphasewasa rich anddiverseresearchprogram
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slightoveralldecreasewith depth.
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which combined the key issues of the various geoscience
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Seismicstructure. The seismicprogramemployeda broad disciplinesinvolved. This hard won scientificconsensusin the
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spectrum of studies, which covered scale lengths from geosciencecommunity helped to keep the debateson site
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kilometers to a few centimeters. These included 2-D and 3-D, selectionat a professionallevelandto ensurethatall disciplines
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near-vertical and wide-angle seismic surveys, VSP were equally involved in the selection decision and in the
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measurements,and more sophisticatedsurface-to-borehole ensuingresearch.
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experiments. These were complemented by petrophysical It was clear from the beginningthat a superdeepdrilling
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laboratorystudiesunderin situ conditions,drill core analyses, programwould exceedthe limits of existing technology.This
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anda varietyof boreholemeasurements.
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technicalchallengeand the strongsupportfrom the German
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The 3-D experiment, the first of its kind in crystalline industry were prerequisitesfor KTB to be consideredfor
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basement,revealed a numberof pronounced,steeplydipping funding as a large-scalenationalresearchinitiative. From the
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reflectorsin the uppercrust. The most prominentof thesewas total budgetof $350 nilIlion US, 50 million were earmarkedfor
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penetrated,as predicted, at a depth of about 7000 m. The scientific projects and an equal sum was allocated to the
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reflectoris a deep-reachingfault systemconsistingof a 400 m industry for R&D projects. The drilling industry was also
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thickgroupof shearzones.The physicalparametersresponsible funded for constructionof a completelynew drill rig, which
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for the observedreflectivity were quantified by integrated involved a number of technical innovations.This greatly
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modeling of data from surface experiments, borehole improvedthe competitivestanceof theGermandrilling industry
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measurementsand laboratorystudies.
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internationally.
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Altogether,the seismicprogramdemonstratedthat most of Approvalfor a fully equippedmodernfield laboratoryon site
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the reflectionsregisteredin the upper crust originatefrom was hard foughtin the planningstagebut it provedto be
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fracturezonesand faults and that lithologicboundariesare of indispensibleand shouldbe includedin any futureprojectsof
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little importance.This is due to the fact that impedance thiskind. The field laboratorystaffcarriedouta broadspectrum
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contrastsproducedby faultingare muchhigherthanthosedue of investigationws hichprovidedthenecessarybackgroundata
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to lithological variations. Furthermore, although the for the numerousresearchprojectsat universitiesand other
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petrophysicasl tudiesand VSP data clearly indicatedseismic institions. An information stream from quasi-continuous
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anisotropyof the rocks,the anisotropyeffect wasfoundnot to analysis of cuttings and drilling fluid (including dissolved
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contributesignificantlyto thereflectivityof thecrust.
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gases),combinedwith datafrom boreholeloggingprovidedthe
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21562202b, 1997, B8, Downloaded from https://agupubs.onlinelibrary.wiley.com/doi/10.1029/96JB03945, Wiley Online Library on [08/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
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EMMERM•N AND LAUTERJUNG' KTB DEEP DRILL HOLE
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18,201
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basisfor an optimumbalancebetweenloggingandcoring,and
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also gave the engineersrapid feedback in case of technical
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problems.
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A lesson learned while drillin• the vilot hole was that the
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_
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_
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DallmeyerR, . D., W. Frankea, ndK. Weber(Eds.)P, re-PermianGeology of CentralatutWesternEurope,604 pp.,Springer-VerlaNge, w York,
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1995.
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DresenG, ., J. DuysterB, . St'OckherRt,. Wirth, andG. Zulauf,Quartz
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project managementmust have a clearly defined chain of
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ContinentaDleepDrillingProgramKTB,J. GeophysR.es.,thisissue
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commandandresponsibilityandthatdecisionmakingmustgive ELEKTB Group,KTB and the electricalconductivitoyf the crust,J.
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equal weight to the concernsof the geoscientistsand thoseof
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GeophysR. es.,thisissue
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the engineeringteam.Thereforethe go-aheadfor
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the superdeep
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EmmetmannR,., The KTB pilothole:Tectonicsettingt,echnicadl ataand firstresultsi,n TheGermanContinentaDl eepDrilling Program,edited
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hole by the Ministry for Researchand Technology was byR. EmmetmananndJ. Wohlenberg52, 7-553,Springer-VerlaNge, w
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conditionalon reorganizationof the projectmanagementT. he
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York, 1989.
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new, and ultimatelysuccessfulm, anagemenst chemeconsisted Emmetmann,R., and H.J. Behr, Location for the superdeepborehole
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of three directorates: geoscience, borehole logging and experimentation,and engineering.The final decisionswere
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confirmedT,ectomq•hysic1s3,9, 339-340,1987. EmmetmannR,., andJ. LauterjungD, oubleX-rayanalysisof cuttingsand
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rock flour:A powerfultool for rapidand reliabledeterminatioonf
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madeby a projectmanagerwith experiencein all threeareas, boreholelithostratigraphSyc,i.Drill., 1,269-282, 1990.
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andhisresponsibilitywasto weightheoftendiverginginterests ERCEUGTGroupA, nelectricarlesistivitcyrustasl ectionfromtheAlpsto
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of the threedirectorates.He was advisedby an expert panel theBalticSea(centraml gmenot f theEGT), Tectonophysic2s0,7, 123-
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made up
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from
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leading scientistsand
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industry representatives.
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139, 1992.
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FrapeS.K., andP.Fritz,Thechemistrayndisotopiccompositionf saline
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This managemenst tructureintegratedindustryexperienceand groundwatefrsomtheCanadianShieldG, eochi•nC. osmochimAc. ta,
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geoscienceconcernsat the decision-makinglevel, and it
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48, 1617-1627, 1982.
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ensureda balanceddistributionof financesand manpowerfor Harjes,H. P.,et at.,Originandnatureof crustarleflectionsR:esultsfrom
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drilling, coring,logging,andthe boreholeexperiments.
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integratesdeismicmeasuremenattstheKTB superdeedprillingsite,J.
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In retrospectw, e believethatthe time givenfor the planning
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GeophysR. es.,thisissue HuengesE, ., B. Enge.•r,J. Erzinger,W. Kesselsa,nd J. Ktick,The
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phase(7 years) and the presite investigations(2 years) was permeablcerust:Geohydraulpicropertiedsownto 9100 m depthJ, .
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necessaryand sufficient. For the purposeof site selection, GeophysR. es.,thisissue.
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however,it wouldhavebeenbetterto havedrilled a technically simple, 2-3 km hole at each site instead of several shallow boreholes(< 500 m).
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KontnyA, ., G. FriedrichH,.J.Behr,H. deWallE, .E.Horn,P. M611ear,nd G. Zulauf, Formationof ore nfineralsin metamorphicrocksof the GermanContinentadleepdrillingsite(KTB), J. GeophysR. es.,this
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issue.
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M611erP, ., et at., Paleo-andrecentfluidsin the uppercontinentaclrust-
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AcknowlegmentsW. e are especiallyindebtedto R. Trumbullfor his
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ResultsfrowntheGern•anContinentadl eepdrillingProgram(KTB), J.
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constructivediscussionasndcritiqueof themanuscriptW. e alsothankU.
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GeophysR. es.,thisissue.
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Harmsfor contributionsto the text and for providingsomeof the figures. The GermanFederalMinistryfor ResearchandTechnologyfinancedand gave full supportto the KTB program.The authorsthank the Deutsche Forschungsgemeinschafoftr continuousfundingof the coordinationof
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O'Brien, P. J., J. Duyster,B. Grauert,W. SchreyerB, . St'0ckherta,nd K. Weber, Crustal evolutionof the KTB drill site:From oldestrelicsto the
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lateHercyniangranitesJ,. GeophysR. es.,thisissue. Pechnig,R., G. Zimmermann,S. Haverkamp,J. Wohlenberg,and H.
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BurckhardtI,ntegratedloginterpretatioin theGermanContinentadl eep
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the scientificprogram(Em 23/14) and for supportingthe scientistsand
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drilling Program:Lithology,porosity, and fracturezones,J. Geophys.
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techniciansof the field laboratory(Em 23/19). Finally, specialthanksare due to the Universityof Giessenfor providingfacilitiesfor coordination of theprogramandadministrativesupportfor thefield laboratory.
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Res., this issue Stoeckhert, B., The "brittle-ductile transition" in the KTB borehole: A
|
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tentative prognosis,KTB Rep. 94-2, 25-34, Nieders,•ichsisches Landesdamftor BodenforschH.,annoverG, ermany,1994.
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Stoll,J., J. BigalkeandE.W. Grabnet,Electrochemicmalodellingof self-
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References
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potentiaal nomaliesS, urv.Geophys.1, 6, 107-120,1995. Wagner,G. A., et al., Post-Variscatnhermalandtectonicevolutionof the
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KTB siteanditssurroundingsJ,. GeophysR. es.,thisissue
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Borm,G., B. EngeserB, . HoffersH, .K. Kutter,andC. Lempp,Borehole Zoback,M.D., andH.-P. Harjes,Injection-induceedarthquakeasndcrustal
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instabilitiesin theKTB mainboreholeJ, . GeophysR. es.,thisissue.
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stressat9 km depthattheKTB deepdrillingsite,GermanyJ, . Geophys.
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Bosum,W., U. Casten,S.C. Fieberg,1. Heydr, and H.C. Soffel,Three-
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Res., this issue
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dimensionainlterpretatioonf theKTB gravityandmagneticanomalies,
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J. GeophysR. es.,thisissue
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Brudy,M., M.D. Zoback,K. Fuchs,F. Runm•el,andJ. Baumg'tirtner,
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Estimationof the completestresstensorto 8 km depthin the KTB
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R. Emmermannand J. Lauterjung,GeoForschungsZentmPmotsdam,
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•ientific drill holes:hnplicationfsor crustalstrengthJ,. GeophysR. es., TelegrafenbergA17, D-14473 Potsdam,Germany. (e-mail: lau@gfz-
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ByefleeJ,.D,,FrictionofrocksP, ureAppl.Geophys.,11661,5-629,1978.
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Clauser,C., et at., The thermalregimeof thecrystallinecontinentaclrust: (ReceivedFebruary14, 1996;revisedDece•nber18, 1996;
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ImplicationfrsomtheKTB,J. GeophysR.es.t,hisissue
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acceptedDecember18, 1996.)
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