JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 102, NO. B8, PAGES 18,179-18,201, AUGUST 10, 1997 The German Continental Deep Drilling Program KTB: Overview and major results Rolf EmmermannandJ6mLauterjung GeoForschungsZentPruomtsdamP,otsdamG, ermany 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. Introduction requireclosecooperationbetweengeoscientistasndengineers,a prerequisitewhichdevelopedintoa fruitful symbiosisL. ike any In October1994, after 1468daysof drilling, the superdeep expedition to uncharted regions, the KTB project was boreholeof the GermanContinentaDl eep Drilling Program meticulouslyplannedto foreseeand minimizepotentialrisks. KTB (KontinentalesTiefbohrprogrammder Bundesrepublik Thusthe projectproceededin distinctphasesa, fter eachof Deutschlandr)eacheditsfinaldepthof 9101 m at a temperature whicha fundamenttaelevaluatiownasmadeandstrategiewsere of ~265øC. The main phaseof the KTB was then concluded redefinedA.ftera preparatorpyhase(1982-1984a) nda phaseof with threemajorexperimentsin the uncasedbottomsectionof presiteinvestigationasndsiteselection(1985-1986),the KTB the hole: a dipole-dipoleexperiment,a draw-downtestand a pilotphasebeganin 1987.Thisinvolvedsinkinga pilotholeto 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 KTB was terminated as scheduledon December 31, 1994. 1990).The resultsof thepilot phasehada majorimpacton The KTB was the largest and most expensiveresearch scientificand technicalplanningof the superdeephole programin the geoscienceesver undertakenin Germany.The CHauptbohrung"K, TB-HB), and providedthe basisfor the Federal Ministry for Researchand Technologycommitteda officialgo-aheafdorthemainphaseA. pprovawl asgiventothe total of 528 million DM (~$350,000,000U.S.) to the project, designand constructioonf a specializeddrill rig with a fromtheplanningphasein 1982throughto completionin 1994. maximumcapacityof 12 km, the targetdepthwassetat the A KTB projectgroupe, stablisheadt theGeologicaSlurveyof temperatulreevelof 300øC(expecteadtabout10km),a budget LowerSaxony,Hannoverw, asresponsiblfeor thetechnicaal nd wasdetermineda,nd a time framefor the main phasewas operational realization of the program. The Deutsche limitedto December31, 1994.The year 1995 wascommitted Forschungsgemeinscha(fDt FG) oversaw and coordinatedall for siteshut-dowanndfinaldataevaluationa,ndonJanuary1, KTB-relatedscientificactivities.At onetime or anotherduring 1996, the GeoForschungsZentrPumotsdam(GFZ) took over this period, more than 700 scientistsand technicianswere responsibilitfyor the final phase.In thisphase,the two drill employedin KTB-relatedwork. holes,whicharesome200 m apart,will beusedovera 5-year KTB fully deservesthe term "superdeepadventure"because periodas a deepcrustallaboratoryfor in situ scientificand it advancedthe frontiersof many geoscientificand technical technicalexperiments. fields.It wasclearfrom the very beginningthatsuccesswould Copyfight1997by theAmericanGeophysicaUl nion Papernumber96JB03945. 0148-0227/97/96JB-03945509.00 Realization of an Idea In 1977 the Senate Commission on Geoscientific Research of theDeutscheForschungsgemeinschafifrtst discussedtheideaof investigatingthe continentalcrust by meansof a superdeep 18,179 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 •oo EMMERMANN AND LAUTEPOUNG: KTB DEEP DRILL HOLE 18,180 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 EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE 18,181 borehole.At that time, conceptualmodelsof the makeupand Collapse of the Variscan orogen started in the late evolution of the continentalcrust were primarily based on Carboniferous(~300 Ma) andwasenhancedby mantle-induced interpretationof the geological record, interpretationof crustalextensionand magmaticactivity which heraldedthe geophysicalimages obtained from various deep-soundingbreak-upof thenewlyassemblePdangeaT.hisepisodecreateda methodsa, ndapplicationof laboratorydatafromexperimental multitudeof Permian(300-250 Ma) bimodal volcanic suites, petrologyandgeochemistrtoy realrocks.The commissiofnelt intramontanebasinsandgrabenstructuresm, anyof whichare thatfurtherprogressrequired"groundtruth"thatcouldonlybe wrench-relatedD. uringthe Alpine orogeny(~100-30 Ma) the obtainedby direct observationthroughdrilling. From the region was affected by compressionaalnd transpressional beginningt,hereforet,wo fundamentagl oalsof globalrelevance tectonicswhich were followedby yet anotherstageof rifting weresingledout:(1) calibrationof crustalgeophysicsa,nd(2) andgrabenformationin theTertiary(since~25 Ma). Manyof studyof thecrustalstressfield andtherheologicablehaviorof theseeventswere accompaniedby magmatismand enhanced the crust.In the ensuingyears,discussionws ithin the whole hydrothermaalctivity,causingthe formationof widespread geosciencceommunityled to a muchbroadedr efinitionof the mineralization. conceptof continentasl uperdeedprilling. In 1984the official This multiply reworkedcentralEuropeancrustis relatively proposatlo establishtheKTB wassubmitteadndfive priority thin (~30 km) andextremelyheterogeneousb,oth laterallyand areasweredefined:(1) thenatureof geophysicasltructuresand vertically. It is distinguishedby regionally variable but phenomenas:eismicreflectorsand electrical,magneticand generally high heat flow values, complex gravimetric and gravimetricanomalies;(2) the crustalstressfield and the magnetic patterns, pronounced seismic reflectivity, the brittle-ductiletransition:orientationand magnitudeof stresses occurrenceof high-andlow-velocitylayers,andzonesof high as a function of depth; (3) the thermal structureof the electricalconductivityat differentdepths. continentalcrust: temperaturedistribution,heat flow, heat productiona,ndheattransport(;4) crustalfluidsandtransport processesfl:uid systemsf,luid sourcesa,ndfluid movements;Site Selection: A Difficult Decision and(5) structureandevolutionof thecentralEuropeanVailscan basement: properties, deformation mechanisms, and geodynamicosf a multiply reactivatedcontinentacl rustal environment. Altogether,more than 40 potentialdrill siteswere initially suggestedb,utonlyfoursurvivedthefinal definitionof project objectives,and the first main selectionconferencein 1983 narrowed the choice to two final candidates, the Schwarzwald From technicacl onsiderationsa,ndbasedon theexpectation and Oberpfalzregions.As existingknowledgewas inadequate of importantchangesin rheologyandreactionkineticsabove to decide betweenthe two, a 2-year programof geological, about250øC,the targetwassetat the 250ø-300øCtemperature petrologicala, ndgeophysicasltudieswasstartedin eachregion. window. This temperaturetarget was combined with the The results were discussed at a final selection conference in objectiveof penetratingat least8000 m into the continental September1986, attendedby over 200 geoscientistosf all crust. disciplines. 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 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 the central Europeancrust. Perhapsbecauseof its relatively young age (typically < 500 Ma), this crustal type differs fundamentallyfrom that sampledby the Russiansuperdeep from shallow-drillingstudiescarried out in both regions especiallyfor thispurposeindicatedthatthetargettemperature of 250ø-300øCmight be encounteredat 7 km depth in the boreholeKola SG3. Neverthelessc, entralEuropeancrusthasa Schwarzwald,whereasit could lie about 5 km deeperin the complexhistory and has been repeatedlyaffectedby major Oberpfalz.Therefore,taking the original depthcriterioninto compressionaalndtensionalprocessesIt. waslargelyformedor reshapedduring the Variscan orogeny(~400-300 Ma), which wasan importantsteptowardthe assemblyof Pangea(at ~300 account,the DeutscheForschungsgemeinschasfetlectedthe Oberpfalz site for the superdeepborehole [Emmermannand Behr, 1987]. The specificscientificattractionsof this site were Ma). seento be (1) its locationin the suturezone betweentwo first- The Variscan belt represents a collage of arcs and microcontinentsresulting from collision of the Old Red Continent(Laurentia+ Baltica + East Avalonia) with Armorica order units of the Variscanorogen;(2) the existenceof an appealingand testablegeologicmodelwhich had far-reaching implicationsfor crustalarchitectureand geodynamics(;3) the and Gondwana.An important rifting phasein Cambrian and Ordoviciantimes(~500 Ma) first separatedthe microplatesof East Avalonia and Armorica from mainland Gondwana and occurrenceof marked gravity, magnetic,and electrical selfpotential anomalies; (4) the expected presenceof seismic reflectors at drillable depths and of an electrical high- createdlargeareasof thinnedcontinentalor evenoceaniccrust. conductivitzyoneat 10 __1 km; and(5) thechanceto testfor The crustalblocksinvolved beganto convergein Ordovician thermal and geochemicalinfluencesfrom the nearbyTertiary time (by ~450 Ma) and were finally weldedtogetherduring a Eger rift. prolongedstageof collisionin the Devonianand Carboniferous (400-300 Ma) to form thepresent-dayVariscides.Incorporation of magmaticarcs and back arc basins,long-distancenappe Two-Step Drilling Concept transport, a final stage of low-pressure,high-temperature metamorphism, and voluminous intrusion of late to Sincethegeologicabl oundaryconditionsandtheirimpacton postorogenigcraniteshavedonemuchto obscurethe recordof the technicalrequirementfsor reachingthe envisageddepth oceansopeningandclosing. targetwerenotknownsufficientlyt,heKTB conceptwasbased 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 18,182 EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE on drilling two holes,first a pilot hole as a sortof "fact-finding about1.5wt % DEHYDRIL-HT,a synthetich,ectoritc-typLei,- mission"andthenthesuperdeepholeitself. bearingNa-Mg silicatewhichyieldeda thixotropics, olid-free, Main objectives of the pilot phase were to acquire a highly lubricantmud system.Later, due to its electrolyte comprehensive set of geoscientific data from core sensitivityc,orrosivebehaviori,nstabilityat hightemperatures, investigations,cuttingsanalyses,and boreholemeasurements and other factors,it was continuouslmy odifiedby adding with which to develop the methodologyrequiredfor optimal HOSTADRILLa, norganicpolymera,ndNaOHplusNa•CO•to evaluation of the superdeephole and to test the geological fix a pH valueof 10 to 11. With increasingtemperaturien the prognosesM. oreover, the pilot hole would reducethe needfor deeperpartsof the KTB-HB (below7100 m) and owingto samplingand loggingin the upper,largecalibersectionof the continuingsmallinfluxesof salineformationwaters,a steady superdeephole and would provide the information on rock deteriorationin rheologicalpropertiesand water-binding propertiesanddrillability, boreholestability,potentialgain and capacityrequireda partialreplacemenbty addinga mixtureof loss zones,temperatureprofile, etc., critically neededfor the different commercial polymers (KEMSEAL, MILTEMP, technicalplanning. PYROTROL). Furthermore, in order to reduce borehole The KTB pilot hole was spuddedon September27, 1987. instabilitietshemudweightwasraisedfrom 1.06kg/L to 1.40 The conceptdevelopedby the KTB engineers,which was to kg/L by addingbarite(seeTable 1 for a summaryof fluid modify a conventionadl rill rig from industryand to combine systemsusedat variousstages). rotarydrilling andwire line coringtechniquest,urnedout to be After completionof the pilothole,a 1-yearmeasuringand very successfulW. ith a high-speedtopdriverotatingsystemand experimentationprogram was conducted,which included a using an internal and externalflush-jointed5 V2inch mining comprehensiveloggingprogram,14 hydrofracmeasurements drill stringwith 6 inch thin-kerfeddiamondcorebits,560 days and a large-scalethree-dimensiona(l3D) seismic reflection of drilling and logging were needed to achieve a basement survey,coveringan areaof 19 x 19 km aroundthe drill site. In penetrationof 4000 m, and a total of 3564 m of excellent April 1990 the hole was caseddownto 3850 m, leavingan quality cores was recovered.By applying straight vertical openholesectionof 150m. Thepilotphasewasthencompleted drillingcapabilitiesthistechniquehasa depthpotentialof 5 to 6 with a first short-termpumptest,whichyielded71 m3 of km andthusmaybe of specialimportancefor futurecontinental basemenbtrineswith highamountosf N2 andCH4 fromthe researchdrilling to intermediatedepths. uncased bottom zone. A prerequisitefor the successof the drilling techniquewas The main resultsof the pilot phase[Emrnermann1, 989], the developmentof a new water-baseddrilling fluid system, whichdeterminedthetechnicacloncepftor thesuperdeehpole, which was undertakenin close cooperationbetween KTB were (1) the considerablyhigher than expectedgeothermal engineersand geochemists.This system met all technical gradientw, hichled to a definitionof thedepthtargetat 10 km requirementsw, asenvironmentallysafeand,for the first time, (correspondintogabout300øC);(2) thelithologicheterogeneity alloweda quantitativegeoscientificmonitoringof the drilled andthecontinuoussteepinclinationof rockunits,whichcaused basementT. he startingcompositionwasa mixtureof waterwith severe deviation of the hole out of the vertical and resulted in developmentof a vertical drilling strategy;and (3) the frequencyof cataclasticshear zones and fluid inflow zones Table 1. Drilling Fluid SystemsUsedin theKTB Main Hole which, in combinationwith the high horizontaldifferential stressesl,ed to the expectationthat boreholeinstabilitieswould Borehole section DrillingFluid System Properties becomea major problemat depth.This resultedin a slimclearancecasing strategyand developmentof water-based, high-temperaturderillingmudsystemdsescribedabove. 0 - 6760m 0.7%Dehydril plasticviscosity9-22mPas (1,sidetrack) 1%Hostadrill densit1y.06g/cm3 Plate 1 showsthe drill rig of the superdeepboreholeKTBHB, UTB 1, which,at a totalheightof 83 m, is thelargestland- NaOH, NarCO, pH 10-11 baseddrill rig in theworld.The rig is fully electricallydriven, 6460- 7220 m (2, correction) 1.5% Dehydril 1.5% Hostadrill NaOH, Barite plasticviscosity29-53 mPas density1.06g/cm3 pH 11 and incorporatesa number of technical innovations and improvementisncluding,for example,an automaticpipehandling system and remotely controlled gear-driven drawworks. 7140 - 8330 m (2, sidetrack) Bentonitc plasticviscosity35-91 mPas KemseaMl,iltemp, density1.25g/cm• Pyrotrol,NaOH pH 10 Barite To ensuresufficientreservest,he drill stringlayout was madefor a maximumdepthof 12,000m (diameterof 5 •Ainch, enhancedsteelquality).By using40 m standsof drill pipe insteadof the standard27 m stands,and in combinationwith the 7460 - 8730 m (3, sidetrack) Bentonite plasticviscosity25-90 mPas KemseaMl,iltemp, densit1y.40g/cm• Pyrotrol,NaOH pH 9-10 Barite 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 8630 - 9100 m Bentonitc plasticviscosity27-59mPas KemseaMl,iltemp, densit1y.40g/cm• downholemotor.It effectivelyminimizedthe frictionbetween drill stringand boreholewall and allowed a 50% reductionof Pyrotrol,NaOH pH 9-10 Barite,Polyglycol the drilled rock volume by realizationof the slim-clearance casingconcept. The VDS systemwas usedto a depth of 7500 m at the All drillingfluid systemsare water-basedD.ehydrilis a synthetic clay mineral (Hectoritc-type)H. ostadrill,Kemseal,Milltemp and maximumallowabletemperatureof 175øCfor the electronics, Pyrotrolare syntheticviscosifiersand organicadditives.NaOH and whosedata were pulsedthroughthe mud to the surface.The Na:CO3 havebeenaddedto controlthepH value.Baritecontrolsthe horizontaldisplacemenatt this depthwas only 12 m, which density. meantthatthe boreholewaspracticallyvertical.The hole then 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 EMMERMANN AND LAUTERJUNG' KTB DEEP DRILL HOLE 18,183 1. Correction for Deviation 1000 rn 1300 rn 2. Correction for Deviation 1800 rn 2000 m 3. Correction for Deviation 2600 m 2700 m track I 1710rnI 199m8 I 2.Side track 3767m ,.,389m3 - 0 1000 2000 3000 -4000 VB HB Paragne•sses Metabasites VariegaSteedquences Major Faults 1. Correction for Deviation 5530 m 5600 rn 13518I" 2. Correction for Deviation 7140 m 7220 m 1.Side track I •o m I track 7460m I m,I track I 8630m ,, 8730m 10000 Figure1. Anoutlineof thefinalboreholceonfiguratiosnh,owintghesidetracksandcorrectionfosrdeviation, casingschemaendlithologicaplrofileof(left)thepilotholaend(right)thesuperdeehpole. deviatedtowardtheNE, almostperpendiculatro thegeneraldip boreholeenlargementsp, referentiallyrelatedto shearzones. of the foliation, andat 9069 m, wherethe final deviationsurvey Below that depth,boreholeconvergence(i.e., reductionof the 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, 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. 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, 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 18,184 EMMERMANANNDLAUTERJUNKGT:BDEEPDRILLHOLE and (3) individual specializedresearchprojectscarriedout at universities and other research institutions. All KTB-related scientific activities were coordinated and Field Laboratory 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 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 Fluids Solids Gases Drillingfluid Fluidsampler ,, Cores Cuttings Rock flour i • , Gas trap Sampler , I I Petrology and Structure Petrography Macrostructures Ore microscopy Microstructures Texture C ore ode ntation Borehole measurements meetings,thematicsessionsa, nd the annualKTB colloquium. As of 1995 a total of over2000 publicationshavecomeout of the variousresearchprojects. 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 Petrophysics Density,Porosityand Permeability, Electricand magneticproperties, Soundvelocities,Heat conductivity, y-spectroscopyS, tressrelaxation , Geochemistry Chemical& mineralogicaclomposition of rocks;Fluid-and Gasanalysis KTB-Database Storage Documentation Correlations Modelling to collect extensivegeoscientificdata on cores,cuttings,rock flour, drilling fluidsandgases.Propertiesandcharacteristic(s1) weremeasuredwhichwerenecessaryfor operationadl ecisions ISpaamrt•pi_eUl•is[nngiv-ersKitTieBs- concerningdrilling, sampling, and testing, (2) had to be determinedon a quasi-continuoubsasisas a functionof depth, Reports (3) aretime-dependenatndthereforehadto be recordedassoon as possibleafter sampling,and (4) were neededfor calibration of boreholemeasurementsand were requiredto guide sample Figure2. A flow chartshowingthe samplingandanalysis schemeof the KTB field laboratory. selection and as basic information for all individual research projects. Apart from establishedmethodsa, numberof new techniques influxes could be identified and localized,facilitating quick were developedand continuouslyimproved.Among them were operationadlecisionsconcerningpositioningof drill stemtests a computerizedreorientationtechniquefor cores,a new tool for anddownholefluid sampling. high-qualitydensityimagingof coresby gammaray absorption Togetherwith the work in the field laboratoryd, ownhole and a four-componendt ilatometerfor the measuremenot f the measurementpslayeda centralrole in thereconstructioonf the stressrelaxion of cores. Becauseof the new drilling fluid drilledbasementandprovidedimportantinformationon the in systemand a speciallydesignedautomaticsamplingsystem,a situ propertiesof the rocks.Prior to KTB therewas little real break-throughwas achievedin the evaluationof cuttings, experiencein the integratedinterpretationof loggingdata rock flour, drilling fluid, and gasesdissolvedin the drilling obtainedfrom crystalline rocks [Pechnig et al., this issue]. fluid. The quantitativechemicaland mineralogicacl omposition Thereforean extensiveloggingtestprogramwasconductedin of cuttings and rock flour was determined using a newly thepilotholeusingall availabletypesof tools,andtheborehole developed combination of X ray fluorescenceand X ray log responseswere calibratedagainstcore, cuttingsand other diffraction, which allowed a reliable reconstruction of the dataprovidedby thefield laboratory. drilled basementwithin 1 hourafter sampling[Emrnermannand During the drilling phaseof the pilot hole, sevenlogging Lauterjung, 1990]. Because the pilot hole was almost campaignswereperformedat variousintervals,mainlyfor data completelycored,it was possibleto comparethe lithological acquisitionand technical purposes.After completionof the profile obtained from direct study of cores with that hole,24 differentexperimentswereconducteda,nda totalof 55 reconstructedfrom cuttings and rock flour analyses.It was toolsweredeployed.On thebasisof theresultsandexperiences demonstratedthat the agreeementwas excellent and that every from thesemeasurementst,he combinationof loggingtoolsfor rock type, even minor lithologicalchanges,fault zones, and the KTB superdeephole was defined and, altogether,266 alteredintervals,hadbeenunequivocallyidentified. logging runs were performed. Although there were some In addition,quasi-onlineanalysesof the drilling fluid, and standard high-temperaturelogging tools available from the gasesreleasedfrom drilling fluid, were performed.These industry, several tools were upgradedespeciallyfor KTB. fluid logs turned out to be very sensitive indicators of Among thesewas a high-temperatureformationmicroscanner cataclastic shear zones and fluid inflow zones. Even minor fluid (FMS) whichcouldbe usedup to 260øC.Figure3 presentsan 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 EMMERMANNANDLAUTERJUNGK:TBDEEPDRILLHOLE 18,185 [ KTB-Oberpfalz HB VMG..LS•.TV.•-_R_.••oBH•TV 14.02.9515:17 / KTB-GP-BM Kiick Figur3e. Summoarftyhemajolorggintogolasndtheirrespecmtiveeasurinintegrvinatlhesuperdheoelpe. AbbreviatiaorneNsGSn, aturgalammsapectroscDoLpLy;,electricraelsistivistyo;nics,eismvicelocitBy;GT, borehgoeleomeTtrEyM' Pte, mperaltougrM'e AGm, agnetomGeLtTeg,r;eochemloicgaglintogolS; Ps, elf potentIiPal,'inductilong;FMS/FMfoI,rmatimonicroscanner/fmorimcraotiimonaBgHeTr;Vb,orehole televieweBr;HGM,borehogleravimeteVrS; P,verticasleismipcrofiling. overviewof themajortoolsdeployedandthemeasureddepth Apartfromarchivingth, emaintaskof dataprocessinwgas sections. tointegrataelldataintoa singlea, ccessibilneformatiosnystem, A newandveryprecisemethodof lithologiecvaluatioonf which was achievedusingthe metadataconcept.Metadata loggingdatawithmultivariatsetatisticwsasdevelopebdy the characterize data sets and include information on data sources use of a broadspectrumof Schlumbergetor ols and the andstructuree,xperimentabloundarcyonditionse,xperimental comparisoandcalibratiownithcorec, uttingsa,ndmudsample methodsl,iteraturea, nd,mostimportantt,heactuallocationof data. This method, which relies on discriminationof thedatasets.The metadataconcepits a basicrequiremenfot r "electrofaciesis"d, iscussebdyPechnigetal. [thisissue]a, ndit therealizationof an integratedd,istributedatabasewhichcan contributegdreatlytotherefinemenotf thelithologipcrofileof beaccessebdy anycomputenr etwork. thesuperdeepborehole. The KTB database "KTBase" is a relational database: that is, it contains material such as tables of measured data and The Information SystemKTBase'. observationadlescription(se.g.,thin sectionpetrographyf)rom Access to KTB Data thefield laboratoryt,hedownholelogginggroup,andthemud KTBhasproduceadnenormouasmounotf dataof variouslogginggroupw, hicharestoredseparatealyndcanberetrieved kinds(descriptivveersusquantitativneumericadlata)from andconnecteidn anywayby theuser.KTBaseis embeddeidn differentsourcesi,ncludingthe field laboratoryb, orehole anapplicatiolnayercomprisinignterfacefsor thepresentation measuremenmtsu,dloggingt,echnicaml onitoringe, ophysicaal ndapplicatioonf KTBdataindifferenwt aysT. heapplications experimentfsie,ld investigationans,d externasl cientificcover administration tasks, telecommunication facilities, investigations. databasemanagementa, nd software modulesdeveloped 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 18,186 EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE especiallyfor the scientific technicaltreatmentof data from The metabasicunits comprisecoarse-and fine-grained drilling projects,includingnumericaland graphicalsoftware garnet-bearingamphibolites(plagioclaseh, ornblendeg, arnet packages. KTBase is now available at the andilmenite),massivemetagabbrowsithrelictophitictextures, GeoForschungsZentruPmotsdam.A hypertextlink is installed and thin layers (up to 6 m thick) of mafic and ultramafic on the home pageof the GFZ WWW server(http://www.gfz- metacumulaterocks. Most rock types display chemical potsdam.de). characteristicosf enrichedmid-oceanridge basalts(MORB); however, normal MORB compositionsalso occur. These Scientific Results metabasicunitsperhapsrepresenst licesof formeroceanfloor formedin a backarcenvironmenotr RedSeatypeoceanic Crustal Structure and Evolution basin. The variegatedseriesconsistsof an alternationof massive The Oberpfalzis situatedat the westernmargin of the garnetamphibolitesf,ine-grainedbandedamphibolitews ith BohemianMassif, the largestcoherentsurfaceexposureof layersof calcsilicataensdmarblesh,ornblende-biogtinteisses, basemenrtocksin centralEuropea, ndit encompasspeasrtsof and paragneissesA.mongthe metabasicrocks,alkali basaltic threefirst-ordertectonometamorphuicnitsof theVariscanfold compositionspredominatewith gradual transitionsinto belt: the Saxothuringianth, e Moldanubiana, nd the Tepla- trachyandesiticrocks (hornblendegneisses).These units Barrandian(Plate 2). This basemenbt lock is separatedfrom constitutea metamorphosevdolcano-sedimentasrysociation 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. boundarybetweenthe Saxothuringianand Moldanubianunits. All threeof theselithologicunitshavesuffereda pervasive This boundaryhasbeenregardedas a suturezoneformedby Barrovian-typme etamorphismat upperamphibolitefacies closureof an early Paleozoicoceanbasinduringthe Variscan conditions(6-8 kbar and 720øC at peak conditionsin the collisionin Devonian/Carboniferotuims es(~400-330Ma). paragneisses)c, onnectedwith an intense ductile deformation The drill site was located in a small, isolated thatproduceadpenetrativfeoliationW. hereatsheparagneisses tectonometamorphiucnit called the ZEV (Zone of Erbendorf- seem to recordprogrademetamorphicevolutionalong the Vohenstrau13w),hich representsa variegatedassociationof sillimanite-kyanbitoeundaraynddo not showanysignsof paragneisseasndorthogneisseasndmetabasicrockswith minor earlierhigh-pressurevents,the metabasicrockscontainrelics metapegmatitesA.ccordingto the resultsof presitestudiesi,n whichclearlydisplaya multistageevolutionfroman early particular lithologic-metamorphiccomparisonswith the high-pressumreetamorphismundereclogitefaciesconditions MiJnchbeMrgassiifnthenorthandpreliminairnyterpretatioofn (P> 14kbarT, > ~700øCf)ollowebdyagarnegtranulitfeacies conventionallymigratedDEKORP seismicprofiles,the ZEV overprint(P=10-13kbar,T=620-720øCp) riorto thedominant had been interpretedas a fiat, bowl-shapedremnantof a amphibolitfeaciesmetamorphism[O'Brienetal., thisissue]. supracrustal nappe complex straddling the New age determinationsusing a broad spectrumof Saxothuringian/Moldanubiabnoundary. In targeting the geochronologmicethodcsonfirmthatthepreVariscaanndearly superdeepborehole,it was thereforeexpectedto penetrate Variscanhistoryof the ZEV is muchmore complexthan througha 3-5 km thick nappecomplexand to drill into the previousltyhoughatndis distinguishebdyat leastwoseparate postulatedsuturezone beneathit. metamorphiccycles[O'Brienet al., this issue].The formation In fact,howevert,heKTB-HBencounteresdteeplyinclined agesof the metabasicrocksare about485 Ma and nearly unitsbelongingto theZEV overtheentiredrilledsectiona, nd contemporaneowuisththeearlyOrdoviciandepositionagl eof no evidencesupportingthenappeconcepwt asfound.Figure4 the paragneissprotoliths.The earliestmetamorphicevent showsa schematicSW-NE profile throughthe ZEV downto recordedin boththemetabasicrocksandparagneissehsasbeen about 10 km which summarizesall availablegeological datedat .•475 Ma, using U/Pb chronologyon zirconand information.The drilled crustal segmentconsistsof an monazitea, ndit appearsthat the relict high-pressurmeineral alternating sequence of three main lithologic units: paragenesepsreservedin the metagabbrocsanbe attributedto paragneissems,etabasiteasnda "variegateds"eriesof gneissesthis Early Ordovician high-pressuremetamorphism. and amphibolites.Most rocks show a penetrativefoliation Furthermorteh,edataimplythattherewasonlya veryshort whichdipssteeplybetween50øand80øto theSW or NE andis time spanbetweenformationof therocks,theirsubductionto at foldedintolarge-scaloepenfoldswithNW-SEtrendingaxes. least40 km, and their subsequenrat pid uplift into shallow Theparagneissheasvea ratheruniformcompositioanndare (cool)crustallevels. madeup essentiallyof plagioclase(oligoclase)q, uartz,biotite, The second metamorphiccycle, that occurred under muscoviteg,arnet,sillimanitea, nd/orkyanite;theycommonly Barrovian conditions,can be bracketedbetween about 405 Ma 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 graywackesinterlayeredat a centimeterto meterscalewhich zones,probablydatingthe regionaldeformation)N. umerousKhas preservedits original compositionalfeatures.Former Ar, 4øAr?Arand Rb-Sr dateson mineralsindicatethat the graywackesshow an equigranularquartz-feldsparfabric, drilledbasemenstegmenta, fter coolingto 350-300øCin the whereapseliticlayersare coarsearndricherin micaand LateDevonia(n-360Ma),stayeidn theuppecrrusat nde, ven typicallydisplaya biotiteflasertextureA. ccordintgo their moreimportanrte,mainetdherefora longtimeperiodwithina chemiccahl aracteristthicepsrotolithwsereratheirmmatuarend narrowdepthandtemperatuirnetervalO. nlymarginaalnd containa significanatmounot f basalticmaterialT.heywere deepepr artsof theZEV wereaffectedby theCarboniferous probabldyepositeadtanactivecontinentmalargin. deformatioandlow-pressuhreig, h-temperatmureetamorphism 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 18,187 EMMERMANNANDLAUTER]UNGK:TBDEEPDRILLHOLE i E 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 18,188 EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE $w Franconian Lineament KTB-HB NE ::::::::: .' .w•'••:.''"""•'•"ii':•"'•i'•'•.?- ?•' ..•:•ii.•:".:• ..:. Figure4. SchematiScW-NEprofilethroughtheZEV in thesurroundinogfsthe KTB site(no vertical exaggerationT)h.e metamorphsicequencoef theZEV hasa polyphasheistoryw, ithearlyhigh-pressure metamorphiastmabou4t75Ma,andlaterB, arrovian-tympetamorphiastmabou4t00-375Ma.TheFalkenberg granitet,o theNE, intrudedat about310Ma. To theSW areforelandsedimentasryequenceosf Upper CretaceouTs,riassica, ndPermo-Carboniferoaugses. (335-325 Ma) which strongly overprinted the neighboring rocksof the variegatedsequenceandareconnectedwith a local basement units. greenschist facies retrograde overprint. These faults are The first evidencefor a commonhistoryof the ZEV and the displacedby reversefaults of possibleCretaceousage, which Moldanubian/Saxothuringiaznonesis the emplacementinto all formed under prehnite-actinolite facies conditions. The theseunitsof late Carboniferousgraniteswhichoccurredin two youngeststructuralelementsare steepnormal faults probably major "pulses",a late tectonicphaseat 335-325 Ma and a relatedto a phaseof grabenformation(Eger Rift) duringthe posttectonicphase at 315-305 Ma. The Falkenberggranite, late Oligocene/Miocene(-25-20 Ma). whichborderstheZEV ontheNE, hasanageof 311 _+8 Ma Figure 4 depicts the major faults encounteredby the (Figure 4). The intrusionof dikes of aplites, calcalkaline superdeepborehole.The most prominentfault system was lamprophyre(sdated by *øAr?Ar at -306 Ma) and penetratedbetween6850 m to 7260 m and consistsof a broad monzodioritesw, hichcrosscutthe metamorphircocksdownto bundleof individualfault planes.Fissiontrackdataon sphene depthsof about7800 m, is closelyrelatedto the granific indicatethat a vertical displacementof more than 3 km took magmatism. place along this fault system in Cretaceoustime. A second The post-Variscahnistoryof theZEV is distinguishebdy major systemoccursbetween7820 m and7950 m, and vertical unexpectedlyintense, polyphasedeformation under brittle displacementtherewasat least500 m. Bothsystemsdip steeply condition[sWagneretal., thisissue]M. ajordeformatiopnhases to the NE and can be directly correlatedwith the Franconian includeintensereversefaultingduringthelateVariscan(.--300 Lineament at the surface. Ma) andCretaceou(s.--130-65Maf)ollowedby normalfaulting Fission track studies on apatite, zircon and sphene,in duringthe Neogene(<22 Ma). The mostwidespreadbrittle combination with investigations of the Permo-Mesozoic elementsin bothboreholesare graphite-bearinlagte Variscan sedimentaryrecordin the westernforelandof the ZEV, provide reversefaults.They occurpreferentiallyin paragneisseasnd a detailed picture of the uplift and cooling history of this 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 EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE 18,189 basementblock and indicatethat a rock pile of about 15 km has gaseousinclusionswith admixturesof CH4 and N•, and often beenerodedsincetheintrusionof the granites.Major phasesof containinggraphite,formedin connectionwith the late Variscan uplift and denudationoccurredduring the late Carboniferous cataclasticdeformation (-300 Ma) and are associatedwith the and Permian(> 4000 m), lower Triassic(>1500 m), and during graphite-containinsghearzones. the Cretaceous(> 3000 m). All are connectedto prominent 'I-'hedominanttype of fluid inclusionsare highly ........ stagesof crustalshortening. Na(e K, Mg)-CI aqueoussolutionswhoseabundancea, swell as A highly unexpectedresult, confirmedby a numberof salinity(upto48 wt % NaCI-CaC•I.•) andCa-contenint,crease independenotbservationsis, thelackof anyP-T gradientsdown significantlywith depth. These inclusionsrepresenta young to at least8000 m and the uniformityof radiometricages.This (<60 Ma) fluid systemthat probablyinfiltrated in connection finding,togetherwith the enormousamountof post-Variscanwith theCretaceousphaseof uplift andfaulting. Subrecentfluid uplift andcrustalthickeningr,equiresa processof thrustingand activity is reflectedin low salinity Ca-Na-CI inclusionsonly stacking.Henceit appearsthat the superdeephole penetrateda foundin the uppersectionof theborehole. pile of steeply inclined thrust slices with the Franconian Secondarymineralsdepositedin faults, veins, and veinlets Lineament acting as the frontal ramp. Furthermore,the data documentfluid activity relatedto the brittle deformationof the suggestthat the slices were detachedfrom a decollement basementT. heir chemicalcompositionand paragenesems irror horizoncoincidingwith the Mesozoicbrittle-ductiletransition the evolution of the respectivehydrothermalsystemsand zone. constrainthe PT conditionsof eachmajor deformationstage.A The geologicstartingmodelprovedto be inaccuratea, ndthe sequencewith decreasingagecanbe establishedfrom actinolite newinsightsfrom theKTB resultswill havea strongimpacton throughclinozoisite,epidoteand prehniteto laumontitewhich ongoingdiscussionsof the structureand geodynamicsof the reflectsa decreasein temperaturefrom about350øC to 160øC CentralEuropeanbasementI.t appearsthattheZEV, becauseof (for laumontite). its high-levelcrustalpositionsinceDevoniantimes,has been The ZEV rockscontaina surprisinglylarge amountof free shieldedfrom theCarboniferousdeformationandhighheatflow fluids,eitherin the form of hydrocarbon-ric"hdry"gasesor as event and thereby preserved important structural and formationwaters.Dry gaseswere only detectedin the gaslogs evolutionaryinformationonthepreVariscanandearlyVariscan and couldnot be sampleddirectly.They mainlyconsistof history.This historyis characterizebdy a doubleP-T loop,with methane with minor helium and radon and are invariably a first, high-pressurleoop as early as Lower Ordovicianand a associatedwith graphitizedfaults. Formationwaterswere first secondB, arrovian-typeloopin theDevonianT. he integrationof encounteredat 400 m depth, and they occur very commonly these findings into the general geodynamic puzzle of from 3200 m downto thefinal depthin numerousdistinctzones reconstructingthe Variscanconsolidationof centralEuropeis of upto severaltensof metersin verticalthicknessB. elow2000 still a matter for further work. Likewise unexpecteda, nd of m the first salinepeakswere detected,and at 3200 m the first considerableconsequencewith respect to geologic models openfissuresand porousalterationzonescontaininghighly basedonsurfacemapping,is theintensebrittledeformationand salinefluidswerepenetratedS.ignificanftluidinflow(upto 30 theenormousamountof thrustfaultingwhichhithertohadbeen m•)occurreadtvarioudsepthlevelsassociatwedithmajofrault regardedas impossiblefor an "anorogenic"intraplatesetting, zonesor were stimulatedby draw downtests[Huengeset al., about200 km northof theAlps. this issue]. The most promisingfluid-containingsectionswere studied Paleofluids and Recent Fluids by in situfluid sampling'andencouragebdy a first successful pumpingtestin the pilot hole,a secondl,ong-termpumping Fluidsin the Earth'scrustform oneof the mostimportant experimen(tfromAugustuntilDecember,1991)wasconducted topicsof contemporargyeosciencea,ndthe superdeepdrill hole in theopen-holesectionof theKTB-VB.460 m3of brineswith offersmanynew andsurprisinginsightsinto fluid processeisn about70 g/L TDS and270 m3 of gaseswerepumpedto the the past and at present.One of the surprisesfor interpreting surface and continuouslyanalyzed (the "4000 m fluid"). metamorphicrocksis that,despitethepolymetamorphihcistory Simultaneousmonitoringof the KTB-HB showedthat fluids of of the various metamorphicunits and the strongDevonian thetwo boreholescommunicatedthrougha networkof fractures medium-pressureoverprint, the primary oxygen and sulfur whichconnectedtheopen-holesectionof thepilotholewiththe isotopicpatternsof the protolithshave been preserved.This intervalbetween3000m and6000m of thesuperdeehpole. implies that metamorphismtook place under nearly closed- The composition of the formation waters changed systemconditionsat low water/rockratios and was not, as has systematicallywith depth,and the followinggeneralvertical oftenbeenpostulateda,ccompaniebdy pervasivefluid flow. sequencewas established:(1) an upper zone of normal The inventory of paleofluids from the ZEV rocks groundwaterextending down to at least 650 m, (2) an encompassegsasesandaqueoussolutionstrappedin nanogram intermediatezone of low-salinity,NaCl-dominatedformation quantitiesas fluid inclusionsmainly in quartz [MOller et al., watersdownto about3200m, and(3) ,moderatetloyhighly this issue].Severalgenerationsand typesof inclusionscan be salineCa-Na-C1basemenbt rineswitha pronounceidncreasein distinguisheadndrelatedto distinctgeodynamipcrocessesT.he salinityandCacontenwt ithdepth.Type2 probablyrepresentas oldestfluid generationpreservedprobablyrepresentsgaseous formationwaterwhichis evolvinginto type 3 by water/rock remnantsfrom the Devonian metamorphismand consistsof interaction. water-freeN2-bearinginclusions(with CH,•or CO2)whichhave Table2 summarizetshemajoranalyticaldataof the"4000m the highestdensities(about750 kg/m3).Moderatelysaline fluid"(representativoef types)which,at atmospheripcressure, NaC1-KCI-MgCaIq2ueouisnclusion(4s-8wt % NaCI•.),which releasedabout0.8 L/L gasesthai weredissolvedunderin-situ areconspicuouselynrichedin theuppersectionof theborehole conditionsT.he gasphaseconsistsof 67.0%N2, 31.6%CH4, (above4500 m), representa fluid systemthat accompaniedthe 0.52% He, 0.14% At, and0.04% CO2.Chemicaal ndisotopic lateCarboniferougsraniticintrusion(s-330 Ma). CO•-dominant datashowthat nitrogenand methanewerederivedby thermal 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 18,190 EMMERMANN AND LAUTERJUNG:KTB DEEPDRILL HOLE Table 2. The "4000 m Fluid" Brine Data Element Na K Li Ca Mg Sr Ba Mn Zn Cu mg/L 7160 231 2.4 15700 2.2 244 1.5 0.13 0.01 0.02 s7Sr/•6Sr 0.7095 •SO -5%o •D - 10%o Ele•nent •ng/L AI Fe SiO2 CI Br F SO4 PO4 HCO, TDS pH Eh <0.015 0.3 54.0 44100 417 3.8 307 0.5 45 68260 8.3(in-situ5.3-5.8) -150 (mY) Gas Data Element N, CH, He Ar CO, vol % 67.0 31.6 0.52 0.14 0.04 •N 3Herlie +0.30,60 6x 10'6 decompositioonf organicmaterialof a marinesedimentary 10'• m2,whichareseveroarl derosfmagnituhdieghetrhanthe source(paragneissprotoliths).The He.isotopicsignatureis matrixpermeabilitoiefstherockassmeasureindthelaboratory dominatedby radiogeniccrustalhelium, with lessthan 3% of undersimulateidn situcondition[sHuengeestal., thisissue]. mantle component which probably originates from the Theformatiopnressurdeseterminefodrthebrine-containing metabasicrocks[M6ller et al., thisissue]. zonesat differentintervalsshowa progressiviencreasewith The chemical compositionof the 4000 m fluid, and depthto a maximumvalue of 105 MPa for the fluids at 9 km. 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. contaminationby recentmeteoricwaters. Application of several independent chemical geothermometers suggests that the 4000 m brine has GeophysicalStructuresand Phenomena experienceda temperatureof about 160øC (equilibrium 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 connectionwith Cretaceousuplift and deformationby dynamicwavefield,constrainotsnthedecisivelementosf the infiltration along the deep reachingfault systemsof the seismicresponsefunctionwerederived. Franconian Lineament. The KTB drill hole was sitedat the intersectionof two Information on in situ permeabilitiesand hydraulic seismipcrofilesD, EKORP-a4ndKTB8502,wherepresite propertiesof the basement,which are critically neededfor investigationhsadindicateadnumbeor f reflectorastaccessible understandingand modelinghydrodynamicprocessesc,ome depths[Harjeset al., thisissue].To obtaina moredetailed 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 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 sw EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE 18,191 8 o KI'B o eeeeeeeeeeeeeeee %eeeeeeeeeeeeee e:© ß ©©ee ß ß eeee©eeeee eeeeeeeeeeeeeeeeee eeeeeeeeeeeeeeeee©e ß ß eeeeeeeeee eeeeeee eee ß .I 15 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." extendsdownto about10 km. The secondgroupof reflectorsis seismograms.Comparison of these with the measured subhorizontalandis "bundled"in thedepthinterval>8.5 to 12 seismogramsshowsa fairly goodagreementO. n theotherhand, 'km. This latter groupmarksa zoneof high seismicreflectivity syntheticseismogramscalculatedusing seismicimpedance which,basedon wide-anglereflectionseismicsi,s immediately valuesderivedfrom compositionadlatameasuredon cuttingsin underlaibnya high-velociztyone(V•> 7 km/s)T. hisprominent the field laboratoryyielded only very small amplitudes.This mid crustal phenomenon, which combines high seismic resultprovesthat the seismicreflectivityof the SEI is not due reflectivity and high P wave velocity, is called the Erbendorf to lithologiccontrastbut is mainly causedby the effectsof body(darkshadingonFigure5). cataclastic deformation. Most of the steeplyinclined reflectorscan be tracedto the Altogether,the geophysicarlesultscombinedwith "ground surfaceandrelatedto known major fault systemsT. he strongest truth" from the boreholehave shownthat steep-angleseismic of these reflectors is the so-called SE1 reflector, which strikes reflectionprofiling, at least in this basementregion, mainly SE-NW and dips 55ø to the NE, has a considerablelateral depictsthe effects of brittle faulting and imagesthe young extent, and crosscutsall lithologic boundaries.It can be deformationpattern of the upper crust. Faulting is also correlateddirectly to the FranconianLineamentat the surface obviouslyresponsiblefor a 2-3 km verticaldisplacemenotf the andclearlyrepresentsits depthcontinuationT. he SE1 reflector subhorizontalreflectors belonging to the Erbendorf body was predictedto 'occur between6600 and 7100 m in the (Figure 5). This body may well be a metabasicrelict of a borehole,and in fact, the most prominentcataclasticfault paleosubductionzone, or a sliver of dense rock emplaced bundleof the KTB, consistingof at least four major fault tectonicallyduringthe Variscancollision.It is thereforea key planesw, asdrilledin thedepthintervalbetween6850and7260 elementin the geodynamicinterpretationof theentirebasement m. Calculationssuggesthatthecontrastof seismicimpedance region,butmoreinterpretivework,andperhapsevenadditional betweenthe wallrocksand the permeable,fluid-bearing,and experimentsw, ill beneededto understandfully its nature. mineralizedfaultzonecanproducetheobservedreflectivity. In thecourseof theinterpretivwe orksummarizeadbovet•he On thebasisof thesefindings,a'specialseismicexperiment KTB seismic group developeda promising new processing was designed whose major goal was to quantitatively methodof true-amplitude,prestackmigrationwhichrepresents understansdeismicreflectorsin the crystallinebasementan importantgeneraladvancein seismicdataprocessingT. his [Harjes et al., this issue].The spatial orientationof the methodis basedon a generaldiffractionconceptinsteadof a reflectingelementSE1wasdefinedaspreciselyaspossiblea, nd reflectionconceptandprovidesa quantitativeandgeometrically thegeometryof theseismicexperimenwt asoptimizedin order correctreconstructioonf thereflectivitydistributionwith depth. to achievemaximumresolutionT. hentheseismicimpedanceof Plate 3 showsa sectionof the KTB 8502 profile which was the rock section between 6500 and 7500 m was calculated from reprocessewdith thismethod.Comparisonwith Figure5 shows borehole measurementsand transformed into synthetic theinterpretivepowerof thenew method. 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 18,192 EMMERMANN AND LAUTERJUNG:KTB DEEPDRILL HOLE Geoelectrics. In the last decade many electromagnetic favorablefreeenergyvalueat therelevantemperature3: CH4q' surveysof continentalbasementregionshave revealeddeep- 2FeS+ 2H•SO4 • 3Cq'2FeS:+8H20. seatedzonesof highelectricalconductivitywhosenatureis still In summaryt,heresultsobtainedoncoremateriaal ndfrom enigmatic.Suggestedcausesof thesefeaturesare the presence various borehole measurements indicate that the basement of saline fluids, interconnectedfilms of graphite or sulfide sectiond, espitetheubiquitouosccurrencoef salinebrinesh, as, 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. extent of such layers at midcrustal levels in the central Intermediatediscretezonesof low to very low resistivity(1 to EuropeanVariscancrust [ERCEUGTGroup, 1992], and they 100 k• m) are in most casesclearly relatedto graphite- were also foundduringKTB site selectionstudiesin both the containingshear zones. Graphite (__+sulfidesth)erefore SchwarzwaldandOberpfalzregions. determinestheelectricalbehaviorof thiscrustalsegment,andit Magnetotelluric surveys and long-period magnetic field appeartshatgeoelectricmalethodcsanimagetectonicprocesses variations indicated a zone of high electrical conductivity andcanbe usedto tracepaleoshearzones. underlyingthe KTB drill site at about 10 km, which has a Gravimetry and Magnetics.The KTB superdeebporehole pronouncedanisotropywith maximumconductivityvaluesin wassitedona strongmagnetiacnomalyandgravityhigh,andit theN-S direction.After completionof thesuperdeepboreholea, was expected that borehole geophysicsand laboratory large-scaledipole-dipoleexperiment(Plate 4), the first of its measuremenotsf rocksamplesobtainedduringdrillingwould kind, wascarriedoutto investigatetheextentandpropertiesof give importantnew insightsinto interpretationof such this high-conductivityzone [ELEKTB group, this issue],The anomaliesP. late5 showsa new,high-resolutio3n-D gravity resultconfirmedthe expectationthat the boreholereachedthis map of the KTB surroundingswhich portrays the density zoneandthat the electrodeat 9065 m depthwasindeedlocated distributionT. he pronouncedgravitylow in theNE corresponds within a layer of highconductivityT. he positionof thislayerat to the Falkenberggranite,and the strongpositiveanomaliesat 9 kin roughlycoincideswith the postulatedbasaldetachment the KTB site are due to metabasicbodies.However,despitea horizon which is related to the post-Variscancrustal thrust relativelylargedensitycontrasbt etweenthemajorrocktypesof stack. the ZEV (paragneisse2s740 kg/m3 and metabasite2s890 Extensivesufacemeasurementswith a variety of electrical kg/m3)t,heirsteepdips,interlayerinagndcomplexstructure methodscarriedout in the KTB surroundingsduringthe presite make lithologic interpretationof the gravity pattern very surveyandthepilot phaserevealedtheexistenceof shallowlow difficult. A partialsolutionto thisproblemcanbe achievedby a electricalresistivityanomaliesandconfirmedthat the drill site combinationof gravity data with results of geomagnetics wascloseto thecentreof an unusuallylargesurfaceanomalyof [Bosumet al., this issue]. the electric self-potential(about-600 mV) extendingNW-SE. The magnetic data give independentinformation about That is, the drill site is situated on a "geobattery"which lithology (inventoryof ferri-magneticminerals)and can also probablydrawsits energyfrom redox potentialdifferencesin portray tectonicfeatures,like mineralizedshear zones. The the subsurface,with graphite-coatedcataclasticshear zones KTB superdeephole penetratedmany magnetic anomalies, actingas electronconductingbridges.The modelpresentedby which have a vertical extent of some meters up to about Stoll et al., [1995] providesa generalexplanationof the nature hundredmeters.One of the mostimportantof theseanomalies, and source of the observed anomalous electric fields. It is with a strongdecreaseof the magneticfield intensity, occurs supportedby downholemeasurementsof the self-potentialand nearthe surface.Below about1200 m the total magneticfield the redoxpotentialobtainedfrom speciallydevelopedlogging intensityincreasessystematicallywith depthwith a gradientof tools. up to 200 nT/km, which is muchhigherthan the undisturbed Hence it appearsthat graphiteis of specialimportancein Earth'smagneticfield would produce(about22 nT/km). This producingthe observedgeoelectricphenomena.Among the result requiresa magneticbody at depth, the exact nature of ZEV rocks, the paragneissescontainprimary graphitewhose which, however, remains unknown.Unfortunately,the deep crystallinityindicatestemperaturesof about700øC, in accord section of the superdeep hole was cased before a high- with the temperaturesof peak metamorphismT. his graphite temperature modification of the magnetometer tool was representsoriginal organic material in the protolithsand is developed.Thereforethe intervalbetween6000 m and 8600 m finely dispersedso that it does not contributeto the overall wasonly measuredby a SchlumbergeGr PIT inclinometertool, electrical conductivity. More important for electrical whose resolution is about 100 times poorer than the conductivityis the secondarygraphite,which is ubiquitousin magnetometertool. Nevertheless, the deep magnetic data cataclasticshearzones,whereit is always associatedwith iron obtainedwith this tool documentthat the strongestmagnetic sulfides and ohiorite. This graphite often forms a quasi- anomalyencounteredin the boreholeoccursbetween7300 m continuous coating along shear planes and is locally and 7900 m. concentratedin millimeter-thick layers which constitutegood Surprisingly,pyrrhotiteturnedout to be the main carrier of electrical conductors over hundreds of meters. rock magnetismin the drilled sequenceand is responsiblefor All the evidencesuggeststhat thisgraphitewasprecipitated mostof the observeddownholemagneticanomalies.Magnetite from hydrocarbon-bearinfgluidsat about400øCand2 kbar. A plays only a very subordinaterole and is restrictedto a few possiblemodeof formationis describedby the reactionCHn+ distinctintervals.It is particularlyenrichedin somepartsof the CO2 • 2C + 2H20. This reactionrequiresa relativelyhigh variegatedseries(marbleandcalcsilicate-bearinagmphibolites) activation energy, which could be providedby mechanical, between7320 and 7800 m, where it producesthe magnetic tribochemical effects in connection with brittle deformation. anomaly mentioned above, which is about 2 orders of Alternatively, since graphiteis intimately associatedwith Fe magnitudehigherthananyof thosegeneratedby pyrrhotite. sulfides,a reactioninvolvingmethaneandsulfatein the system The pyrrhotitecontentin paragneisseasndmetabasicrocksis C-O-H-Fe-S could also be considered, which has a lower, more very similar and mostly below 1 wt %. Enrichmentsup to 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 18,193 EMMERMANN AND LAUTERJUNG:KTB DEEPDRILL HOLE 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 18,194 EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE v r n ¾I 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). KTB 0'-. -15--o0• -25. -30. SW -35 - s -40 • -45 - -50 -. 448O• 4490 "• / 5540 / 5530 4500 • / 5520 /•i/ot4o5e14t•52e00 r•e/•/ sso5o 510 453O 549O Plate5. Three-dimensiongaral vitymapof theKTB surroundingssh,owingthegravityhighat thedrill site causedby metabasiteosf theZEV, andthepronouncegdravitylowsrelatedto theFalkenbergranite(F) to the NE andtheforelandsediments(S) to the SW: 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 EMMERMANNANDLAUTERJUNGK: TBDEEPDRILLHOLE 18,195 iii ml i i i iii i i i Dme)•o0t.h............T...emperat.u..r.e..3..0..0... •:.'. • .... o •.' • 2000 --'-'-,•, .............. :'•.\..••.•. _ • . , 4000 .. ....... ! ! '' '• • '-"'" ••',t•'• ..... •___'._'._ k ',. •......•........ '. '. '. 'k',-- T(Gradti2e8nfWkm) 6000 .,. . ....,.. .., . . .• .. . ., T•mperal:u•e•redi , , (cacOlated19•6) , _ " •' •1, • lit••u,•nt • ß ; %• &/• II 8000 ................ • '. " --- • ß • , ß • Finacl repht9'101m • '. •....m,..• ' •.measu4r8•dhafter ..... •th. elast:gir•:u•...•.ati• 10000 ......... • '. '.,.. 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 predictedfrom the6000 m BHT andbasedon 31 K/km and28 K/kin. 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 18,196 EMMERMANNAND LAUTERJUNG:KTB DEEPDRILL HOLE severalweight percentare typical for hornblendegneissesand wasalsodesignedw, hichprovideda wealthof newinformation all major shear zones. Since it was known from laboratory aboutthe thermalstructureof the drilledsegmenat ndled to experiments that pyrrhotite occurs in at least two low- improved methodsof handling downholetemperature temperaturepolymorphs, a monoclinic ferrimagnetic and a measurementsT. able 3 presentsa summaryof values for hexagonalantiferromagneticmodification,and that the Curie thermalconductivityand heat production.Rock foliationand temperatureof this mineral is around 300øC the superdeep microcracksare responsiblefor significantanisotropyin borehole offered an ideal opportunity to study the in situ thermalconductivit(yupto 20%), withhighesvt aluesparallel magnetomineralogical properties of this hitherto poorly to foliation.The distributionof heatproductionwith depth investigatedmineral[Kontnyet al., thisissue]. reflectslocallithologiesT.he data,in generals, howa slight Among the most important results of this study is that decreasbeutdefinitelydo notconfirmthewidelycitedlaw of frequently, both monoclinic and hexagonalpyrrhotite occur an exponentiadlecreasoef heatproductionwithdepth(Figure together,mostlyin intimateintergrowthsw, ith the monoclinic 6). polymorph being dominant in metabasic units. Hexagonal Geothermadlatafromthesuperdeebporeholeareconsistent pyrrhotite is the stable phase at higher temperatures(above withtheresultsandpredictionfsromthepilothole.Withinthe about 220øC) and it predominates below 8000 m. The upper1500m thetemperaturegradientincreasedfrom 20 K/km observations of monoclinic pyrrhotite grains with relict to about 28 K/km at 1500 m and remained at that value down to hexagonalcoresindicatelow-temperaturetransformationfrom the final depth.On that basis,the undisturbeedquilibrium an originally hexagonal phase during uplift and cooling. temperatureat 9100 m is about265øC.Within uncertaintyt,he Accordingto experimentalfindingsthe Curie temperatureof verticalheatflow densityw, hichis theproducot f temperature hexagonapl yrrhotitemightbe aslow as260øC.It is well known gradientand vertical thermalconductivityi,s also constant from laboratorymeasurementsthat the magneticsusceptibility below 1500 m, with a mean value of around 85 mW/m'. increasesstrongly at temperaturesjust below the Curie Estimationof thecontributioonf thecumulativheeatproduction temperature(the Hopkinsoneffect), and one of the open rateto theverticalheatflow densityshowsthattheupper6 km questionsrelevantto the boreholemagneticstudiesis whether of the penetratedbasemenot nly provideabout10% of the the Hopkinsoneffect contributessignificantlyto the observed calculatedheatflowdensityvalueof 85 mW/m'at 1.5km. If anomalousdepth gradientin the magneticfield intensity,or this value is typical for the crust, then a shift in the thermal whetherthe magnetite-containinlgayer is sufficientto produce gradienttolowervaluesmustoccurwellbelow10kmdepth. this phenomenon. The results of thermal studies in the two boreholes raise a The geopotentialfields, electric, gravity, and magnetic, number of basic questionsabout the heat budgetin the provide complementaryinformation. Whereas geoelectrics continentaclrust.Oneof theproblemsis howtoexplainthelow mainlyimagetectonicfeaturesandgravityprovideslithological thermalgradientin theuppermost1500m, andhowto reconcile information,geomagneticscarry informationaboutboth. The the--25mW/md' eficiitn heatflowdensitbyetweetnheupper combined evaluation of data from the three sources, now and lower boreholesectionsT. hree alternativesare currently underway, will contribute to a detailed 3-D geologic discussedw, hichmayworkin concert:(1) topography-enhanced reconstructionof theKTB surroundings. heat advection by groundwater flow; (2) paleoclimatic Geothermalstudies.Evaluationof thegeothermadl atafrom perturbationof thesteadystatetemperaturefield dueto changes the KTB pilot hole providedthe highly unexpectedresultthat of the meansurfacetemperature(e.g., in connectionwith the the thermalgradient(21 K/km) and verticalheat flow density last ice age); and (3) disturbancesof the steady state (55mW/m')metthepredictevdaluesonlyintheupper1000m. temperaturefield due to lateral refraction of heat flow in a Both parametersthenincreasedrapidly to about 1500 m, after compositionallyandstructurallyvery heterogeneoussubsurface which almost constantgradientsof 28 K/km and heat flow [Clauser et al., this issue]. valuesof 85 mW/m'prevailedT.hetemperatuirne thepilot Modeling of available data prove that both groundwater hole at 4000 m was 119øC and lay well above even the upper advectionand paleoclimaticeffects are able to producethe error limit calculated from the data obtainedby the shallow- measurednear-surfacethermal gradient and heat flow, but the drilling geothermalstudies(Plate 6). exactcontributionof eachprocesscannotyet be quantified.In The desireto explainthe failed prognosisled to an ambitious any case, the observationsclearly demonstratethat external research effort [Clauser et al., this issue]. The KTB field lab factorsinfluencethe near-surfacetemperaturefield in the crust, carried out a large numberof measurementson core material and this suggeststhat values of geothermalgradientand heat andcuttingsto determinestatisticallysoundvaluesfor thermal flow from shallowdrill holesin crystallineterranestend to be conductivity,heatdiffusion,andheatproductionto be usedin systematicallytoolow. thermal modeling. An extensivegeothermallogging program Another set of problemsis raised by the surprisinglyhigh Table 3. Parameters Used for Geothermal Calculations Paragneisses HornblendeGneisses ThermalconductivityW, /m K Heatproductionla, W/ms Naturalgammaactivity,c/skg Potassium,wt % Uranium,ppm Thorium,ppm 1.50+ 0.19 51 ñ 5 3.4 ñ 0.2 2.24 ñ 0.25 2.8 ñ 0.4 7.9 ñ 1.0 1.15ñ 0.11 39 ñ 5 2.8 ñ 0.2 1.9 ñ 0.22 2.0 ñ 0.2 5.7 ñ 0.8 Amphibolites 0.53 ñ 0.28 23 ñ 7 2.6 ñ 0.2 0.88 ñ 0.42 1.0ñ 0.6 2.5 ñ 1.5 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 EMMERMANNANDLAUTERJUNGK' TBDEEPDRILLHOLE 18,197 . '""'"•' "':..... ß.:..:.•",'. .:•;•'.•...... ß..'...:.:,.•v..:•,•_..•..•::-•'l,.'.';.-•.:.;.. .....:•œ.-.•.g,-?.2.'.'.,:.:•. .: '•. ß .,t.,. ß 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 .... under_in situ conditions down to mid crustal levels. Current understandinogf the rheologyof the continentacl rustis based primarily on laboratorystudiesof rock strengthundergreatly •......'.' .•,•A?•..:.•:.,:•. simplified conditions.These studiesindicate that two major processescontrolthe mechanicalbehaviorof crustalrocks:(1) "ß• •.. .:,•..•!".'"' . .. In upper crustallevels, deformationcausesbrittle failure and rock strengthis limited by frictional strengthof preexisting faults. Becausethe frictional strengthincreaseslinearly with '?';'tg•;•:-.':.:-.' confining pressure,the strengthof the crust correspondingly increaseswith depth. (2) At greater depth, beyond a certain .r•: •'.:,. temperatureand at low strainrates,rock strengthis determined by flow laws and decreasesexponentiallywith furtherrise in temperature. ......'., .•/, ß ß ß(.'-d:•.-',•...•ß. . ....;..?..'•a:.v.,.. . ß....:: , .•..[.;.,... ' •:;Z•..:...... ß ...''....:12.[. :......:... ß ,.. _ . . ß-.' ..s.•&-•.::' '::'-"'"' ß....•..:;•.-•j¾.:...:.:. ß 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 broadtransitionzonecanbe expected.Most modelsof rheology are basedon the mechanicalpropertiesof quartzbecauseof its abundancien continentacl rustalrocks.Accordingto the "quartz model"(Figure7), thereis a linearbuildupof differentialstress with depthin the crustto the brittle-ductiletransitionat about 300øC,after which rock strength,and thus the magnitudeof 0.0 1.0 2.0 3.0 "stored"stressf,allsexponentially. Obviously,thereare shortcomingisn sucha simplemodel. HPR [laW/m3] Apart from uncertaintiesin the physical-mechanicaplroperties of mineralsandrocks,a morefundamentapl roblemis that the Figure 6. Diagram showingthe changesin heat production thresholdtemperaturefor ductileflow is criticallydependenotn values,as measuredby laboratoryexperimentsand downhole strainrate,andrealisticstrainrates(10'•ns'• to 10'• s'•) are logging, with depth in the superdeepborehole.The commonly unattainablein the laboratory.On diagramslike Figure 7, the cited exponentialdecreasein heat productionwith depthis not confirmedby thesedata.Instead,onefindsintervalsof constant expectednaturalsituationis thereforedepictedas a continuous averageheat production(vertical lines) which correlate with transitionfrom thebrittleto theductileregime. lithologicchanges. With a basaltemperatureof about265øC,theKTB superdeep hole has penetratedinto depthsin which the brittle-ductile transitioncan be expected,and thusa uniqueopportunityis available to study this fundamentalregion in situ. The most valueof 85 mW/m2for theheatflowdensityat 8 kmdepth. importantelementsof thesestudiesare the determinationof the Extrapolationof the temperaturegradient measuredin the stresstensorwith depth and the structuralanalysisof rocks superdeephole using conventionalmodels for the lower crust fromdepthapproachingthetransitionzone.Fromthebeginning and assuming conductive heat flow leads to predicted of the KTB program, geoscientistsand engineers worked temperatureswell above800øCand heat flow densitiesof 55 to closely together to develop an integratedstressmeasurement 80mW/m2at thecrust/mantbleoundariny 30kmdepthT, here strategy that involved a number of different methods and is no evidencefor partial meltingat this depthfrom seismic experimentswhosecommongoal was to establisha continuous data, and there are also other reasons to expect lower temperaturefsor thecrust/mantleboundaryT. hereforeonemust questionthe model assumptionsI.s there an additionalheat source in the crust below the drill site? Could the Erbendorf 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]. bodybe responsiblefor highheatproductionor are thereeven The magnitude of the least horizontal principal stress 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 heattransportincorrect,and can fluid convectionrelatedto the between800 m and 3000 m), and by two modified hydraulic FranconianLineamentexplainthedilemma? fracturing experimentsat 6018 and 9070 m depth in the Theseand other ideaswill be explorednumericallyand superdeephole.Theseexperimentsyieldedinprecisevaluesfor 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 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 18,198 EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE differential stress , ', criteriom for friction- ',,,••r ..•" controlslelidding \, transitionI alß, .•. •=10'•e range /.•':'•,, "britptleastircansition" --300 øC ,,•,," ,, ....... •= 10-14 KTB / - depth (z) T = f(z) p = f(z) flloafwoqwruartzite strainrate• as indicated[s-•] (dislocationcreep) 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. lithology of the drilled sectionand density of the respective hundredsof metersfrom the injectionzonein the depthrange rock types,is a principalstresscomponenta, continuousprofile between8 and9 km [ZobackandHarjes, thisissue]. of the complete stress tensor down to about 9 km was The inducedseismicitywasrecordedby a surfacenetworkof established. 70 stationsandwith a three-componengteophonetooldeployed The combined results of all stress measurements indicate that at 4 km depthin thepilot hole.Clusteranalysisshowedthatthe 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 andit correspondwsell with theN146øEregionalorientationof borehole.Fault planesolutionsof the seismiceventsindicatea S, in centralEuropeT. he only significancthangeof Ss with strike-slipcharacter,andthisdocumentsthatthecrustat 8-9 km deptihsa shifot fabou6t0ø,toN220øWat,7200mwhichis stillin a stateof frictioneaql uilibriuHmo.wevetrh,e coincidwesiththelowermofasut ltplaneof theSE1fault compleatbesenocfeinduceedarthquankeeas9r 030mdepth, bundlVea. lueosfthemagnituodfSe,at6018mand9070m couplwediththeobservatthioatntheseismeivcenctslustering depth in the superdeephole are 111 MPa and 183 MPa, at a depthof about8.7 km, indicatesan abruptchangeof the respectively,andthe estimateddifferentialstressesare between stressstate,and markedlylower shearstressessuggesthat the 180 MPa and 147 MPa. Apart from theuppermosst ectionof the bottomof theboreholemay benearthebrittle-ductiletransition. drill hole downto about1000 m, whereS. appearsto be the A different approachto identifying directly the current leastprincipasl tresst,hestressmagnitudeosbtainedfromS,,Ss brittle-ductiletransitionzone comesfrom combiningdata on the presentstateof stresswith the resultsof microscopicand andSv(-240 MPa at 9100 m) indicatestrike-slipconditions(S,