alan
/
zotero
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity
zotero/storage/4C4AWW8A/.zotero-ft-cache

2327 lines
105 KiB
Plaintext
Raw Normal View History

the big one
2024-08-27 21:48:20 -05:00
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, <S,< S.).
submicroscopitcexturalstudiesof minerals,especiallyquartz, in the suspectedepthrange[Dresenet al., thisissue].Because
The datasupporthe hypothesisthatthe stateof stressin the the rate of processeswhich control quartz texturesincreases
brittle crust is limited by the frictional equilibrium on exponentiallywith increasingtemperaturei,t wasexpectedthat
preexisftainuglatsndthatthecontineunptaplcerusatctassa significcahnat ngienstexturfaelaturwesouladppeoarn
stresgsuidaendiscapabolfetransmitftoinrgceosfhundreodf sapproachthinetgransitizoonneT.herefoqrueartfzromcutting
megapasccaolsm, paratbolethosexertebdy plate-drivisnagmplteaskeqnuasi-continuboeulosw7ly000mwasanalyzed
processes.
by opticalmicroscopyandtransmissioenlectronmicroscopyI.n
The urgentquestionof whetherthe brittle-ductiletransition general,the quartzmicrotexturesare similar within the depth
wasencountereidn the KTB superdeephole canbe answered interval 7-9 km; however, there are systematicqualitative
with a definite"maybe."One of the mostimportantlinesof changes with depth. These include an improved spatial
evidencecomesfrom a large-scalehydraulicfracturingand organizationof dislocationsd, ecreaseof dislocationdensity,
fluid injectionexperimenct onductedin theuncasedbottomhole and submicroscopifcluid inclusionsand indicatean increasing
sectionat theconclusioonf drillingandwasespeciallydevoted rate of thermallyactivatedrecoveryprocessesT. hesefindings,
to testingthe brittle-ductiletransitionhypothesisW. ithin 25 like those of the hydaulic fracturing and fluid injection
hours2,00m3ofluidwereinjecteidntothecrusat tabou9t030 experiments,indicatethat the superdeephole might have, in
m and some 400 microearthquakewsere triggereda few fact, reachedthepresent-daybrittle-ductiletransitionzone.
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
18,199
Deep Crustal Laboratory: A TelescopeInto the
Earth's Interior
levels. This was done using a combinationof hydraulic fracturingtestswithanalyseosf compression(barleakoutsa)nd
tensilefailures (drilling-inducedfractures)of the borehole
A detailedpictureof thecrustalsectionandits propertieshas walls.Thestudyhasshownthatthebrittleuppercrustis strong,
been assembled from the field experiments, laboratory "stress-loadeda,"nd capableof sustainingand transmitting
investigationsand boreholemeasurementsof the KTB main forcesof plate-drivinmg agnitudeT.hegeneratioonf hundreds
phase.Duringthenext5 yearsof thefinal phase,supplementary of microearthquakbesy extremelysmall increasein pore
experimentsare plannedusingthe globally uniqueassociation pressur(e< 1 MPa)indicatetshatstresslevelsthroughouthte
of two deep boreholesinto the crystalline basementwith a brittlecrustarenearits frictionalstrengthandthatonly a small
separationof 200 m.
stressincreaseis necessartyo inducefailure.Thesefindings
Two main objectives of this so-called "Deep Crustal provethevalidityof experimentaldlyerivedtheoreticasltress
Laboratory" have been defined: (1) The discrimination of profilesa,ndconfirmthatcrustasltrengtihn situdependosnthe
geophysicalsignalsgeneratedby deep-seatedprocessesand by frictionasl trengthon preexistingfa, vorablyorientedfractures
shallow events. Conventionaldeep-soundingmethodscan be with coefficientsof frictionin therangeof 0.6 to 1.0 [Byerlee,
interfered with by effects induced at the Earth-Atmosphere 1978].
interfaceand disturbedby structuresand processesat shallow The brittle-ductile transition. The lack of induced
depth. (2) Determinationof equilibriumvalues of physical microearthquakebselowabout9 km suggesttshatthebottomof
parametersandtheirlong-periodvariationswithtimeanddepth. thesuperdeepboreholeis closeto thepresent-daybrittle-ductile
Theseobjectiveswill be tackledby deploymentof instruments transition.This hasbeenconfirmedby detailedstudyof quartz
at variousdepthandtime intervals.
microstructureisn gneissesw, herestrainis partitionedbetween
Altogether,threegeneraltypesof experimentsare planned: brittle fracture, solution/precipitationcreep, and plastic flow.
(1) Stationary registrationof time-dependentvariations of Measurementsof the dislocation density in quartz, which
physical parameters at different depths under "natural" decreasestowardthe bottomof the borehole,yield differential
boundaryconditions:plannedinvestigationsincludelong-term stressesof about 140 MPa, which approximatelyequal the
measurementosf the seismicity,tidal effects,deformation,and confining pressureat that depth. Thus the emprical Goetze
naturalelectromagnetiecvents(in addition,depthprofilesof criterion also indicatesthat plastic flow contributesto rock
equilibriumfield valueswill be registered(e.g., temperature, deformationat final depths[Dresenet al., thisissue].
heat production)),(2) experimentsu, niqueor repeated,with Crustal fluids and rock permeability. Mixturesof aqueous
defined changes in boundary conditions (e.g., downhole and gaseousfluids are widespreadin the upper9 km of the
measurements of seismic surface vibrations and active electrical continental crust sampled by the KTB. Fluids are mostly
experimentsor hydraulic/fluidtests),(3) cross-holexperiments confined to faults and fractures, and these were encountered,
(the useof two holesallowsspecificexperimentsto investigate even at bottom hole depths,in numerousdistinct zonesup to
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
naturalconditions)A. particularbenefitof the closeproximity magnitudehigher than the matrix permeability of the rocks.
of the two deep boreholesis the ability to perform seismic Formationpressuresdeterminedin brine-containingzonesshow
cross-hole experiments with higher frequencies and thus a nonlinear increase with depth, probably due to stepwise
improvedspatialresolutionT. his typeof experimentswill close increasesin salinity.The formationpressureof 103 MPa at 9
the gap in scale factor between laboratory measurements km is near-hydrostaticT. his, and the fact that experiments
(centimeterrange),boreholemeasurement(sdezimeterrange), proveda hydraulicconnectionbetweenthe pilot hole and the
seismicfield experiments(kilometerrange) and seismology main hole, indicates that fluid pathways are highly
(100-1000 km range).
interconnected.
Finally,it is plannedto expandintoa 3-D triangulararrayby The compositionof the fluids varies systematicallywith
sinkinga thirdholedownto about1000m andtherebycreatea depth:groundwaterin the upperlevels,NaCl-dominatedfluids
greatly improved"telescope"into Earth's interior. With this of low salinityat intermediatedepths,andhighlysaline,Ca-Na-
configurationthe DeepCrustalLab will providea platformfor C1basemenbt rinesbelowabout3200 m. The lattercontainhigh
high-resolutioninvestigationsof anisotropyand transport amountsof dissolvedgas (~0.dL/L of brine), mainly nitrogen
propertiesin thevicinityof thesiteandwill greatlyimprovethe and methane,which is derivedby thermaldecompositioonf
discriminationbetweendeep-seateadndnear-surfaceeffectsand organicmaterialin the paragneissprotoliths.Data suggesthat
processes.
Permo-Triassicevaporitesin the sedimentarybasinwestof the
drill site are the ultimate source of the brines, which have
Conclusions
infiltratedthebasemenatlongdeep-reachinfgaultsystemsdown to at least 10 km depth.
In this paper we attemptedto summarizethe scientific Graphite and geoelectricanomalies.Despitetheubiquitous
advancesgainedby the continentaldeep drilling program,the presenceof salinebrines,the electricalresistivityincreasesi,n
KTB,withrespetcotallofthemajorresearcthhemeSs.omoef generaflr,om103C]matsurfacteo l0sC]mat9 kmdepths.
theresultws illhaveth6irgreatesimt pacitn advancinreggionalLocal anomalies, at various depths, with extremely low
studies, whereasothers are of general significance.In this resistivity(1 to 100fi m) areclearlyrelatedto graphite-bearing
conclusionwe pick out thoseaspectsof the KTB scientific shearzones.Graphitein suchshearzonesis interconnectedover
programwhichareprincipallyof globalimportanceandwhich distancesof hundredsof meters, and this phenomenon
couldnot havebeenobtainedwithoutdrilling.
obviouslydeterminesthe electricalresponseof the basement.
Stress field. A continuousprofile of the complete stress Before drilling, a prominentlow-resistivitylayer of regional
tensor has been obtained from the surface down to midcrustal extentwaspostulatedat about10 + 1 km depth.This zonewas
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
18,200
EMMERMANN AND LAUTERJUNG: KTB DEEP DRILL HOLE
the target of a dipole-dipoleexperimentconductedin the The complexity of the drilled crustalstructuresinspiredthe
boreholeaftercessationof drilling. It turnsout thatthebottom development of a new seismic processingmethod (true
depthof the KTB is well within this majorconductorw, hose amplitude,prestackmigration) and demonstratedthe need to
positioncoincideswith a postulatedbasaldetachmenzt one of consider3-D aspectsin seismicimaging. The new method
the post-Variscanthrusts(Mesozoicbrittle-ductiletransition). providedhigh-resolutioinmagesof themidcrustandlowercrust
An importantimplicationof thesefindingsis that geoelectric at the KTB site. It has been and will continue to be used for
surveyscouldbeusedto mappaleosheazronesandthushelpin reprocessingand reinterpretationof existing seismic records,
tectonic reconstructions.
for example, the DEKORP data, and thus holds great promise
Thermal structureof the crust.A majorlessonof theKTB for newinsightsintothedeepstructureof crystallinebasement.
is that geothermaldata obtainedfrom shallowwells shouldbe
usedwith greatcautionin makinggeothermapl rognosesT.he Looking Back thermasl tructuroef theuppermos1t500m of thecrustis highly
disturbedI.n thisintervalthe geothermagl radientis about21 As this paper goesto press,we look back on 19 yearsof
K/km and the heat flow reachesvalues of about 55 mW/m2. involvemenitn theKTB programs, tartingin the first planning
Both parametersthenincreaserapidly to about27.5 K/km and stagesin 1977, to thecessationof drilling in 1994, andon to the
85mW/m2,respectivealyn,dremainclosetothoselevelsright final phase of on-site experimentationin the Deep Crustal
responsiblefor the near-surfaceeffects: heat advectionby LaboratoryT. he successof theKTB programdependedonclose
topographically induced groundwater flow and surface cooperationamong diverse groups including ministries and
temperaturefluctuationsdue to paleoclimate.The effect of agencies, management teams and engineering units from
paleoclimateis dominant.In particular,the last ice age is industry and academia,and not least the scientists,those
responsiblefor a perturbationof up to severaldegreesin the assignedto the KTB field laboratoryand scientistsfrom
present-daytemperaturedistributionof the upper4 km. Below universities and researchinsitutes. It might be useful to
about2000 m, advectionis negligibleandheattransporct anbe summarize,from ourcurrentperspectivew, hatwe believewere
describedby a purelyconductivemodel.
the key elementsfor the successof the German Continental
The KTB has fostereda numberof importantadvancesin Deep Drilling Program and what we would probably do
interpretingand modelingheat flow data. For example,the differentlya secondtime.
intimatealternationof gneissand metabasiteunitswith near- The singlemostimportantfactorwasthe continuingsupport
vertical contactswas ideal for studyingthe effects of lateral andparticipationfrom the geosciencecommunityin Germany,
refractionof heat flow and for developingnew modelswhich both from the professionalsocietiesand steeringcommittees
take theseeffectsinto account.The large amountof datafrom and from the leadingindividualsin most branchesof the solid
loggingand from laboratorymeasurementcslearly refutedthe earthscienceswhoparticipatedin theprogram.Thisbroadbasis
widely held assumptionthat heat-producingelements are of supportresultedfrom a long conceptfinding phase,which
strongly concentratedin the upper crust and then decrease lastednearly7 years,andduringwhichthe fundamentaal spects
exponentially with depth. Instead, the data show that heat andgeneralphilosophyof thedrilling programwerediscussed.
productionis controlledby lithology,and thereis only a very The resultof thisphasewasa rich anddiverseresearchprogram
slightoveralldecreasewith depth.
which combined the key issues of the various geoscience
Seismicstructure. The seismicprogramemployeda broad disciplinesinvolved. This hard won scientificconsensusin the
spectrum of studies, which covered scale lengths from geosciencecommunity helped to keep the debateson site
kilometers to a few centimeters. These included 2-D and 3-D, selectionat a professionallevelandto ensurethatall disciplines
near-vertical and wide-angle seismic surveys, VSP were equally involved in the selection decision and in the
measurements,and more sophisticatedsurface-to-borehole ensuingresearch.
experiments. These were complemented by petrophysical It was clear from the beginningthat a superdeepdrilling
laboratorystudiesunderin situ conditions,drill core analyses, programwould exceedthe limits of existing technology.This
anda varietyof boreholemeasurements.
technicalchallengeand the strongsupportfrom the German
The 3-D experiment, the first of its kind in crystalline industry were prerequisitesfor KTB to be consideredfor
basement,revealed a numberof pronounced,steeplydipping funding as a large-scalenationalresearchinitiative. From the
reflectorsin the uppercrust. The most prominentof thesewas total budgetof $350 nilIlion US, 50 million were earmarkedfor
penetrated,as predicted, at a depth of about 7000 m. The scientific projects and an equal sum was allocated to the
reflectoris a deep-reachingfault systemconsistingof a 400 m industry for R&D projects. The drilling industry was also
thickgroupof shearzones.The physicalparametersresponsible funded for constructionof a completelynew drill rig, which
for the observedreflectivity were quantified by integrated involved a number of technical innovations.This greatly
modeling of data from surface experiments, borehole improvedthe competitivestanceof theGermandrilling industry
measurementsand laboratorystudies.
internationally.
Altogether,the seismicprogramdemonstratedthat most of Approvalfor a fully equippedmodernfield laboratoryon site
the reflectionsregisteredin the upper crust originatefrom was hard foughtin the planningstagebut it provedto be
fracturezonesand faults and that lithologicboundariesare of indispensibleand shouldbe includedin any futureprojectsof
little importance.This is due to the fact that impedance thiskind. The field laboratorystaffcarriedouta broadspectrum
contrastsproducedby faultingare muchhigherthanthosedue of investigationws hichprovidedthenecessarybackgroundata
to lithological variations. Furthermore, although the for the numerousresearchprojectsat universitiesand other
petrophysicasl tudiesand VSP data clearly indicatedseismic institions. An information stream from quasi-continuous
anisotropyof the rocks,the anisotropyeffect wasfoundnot to analysis of cuttings and drilling fluid (including dissolved
contributesignificantlyto thereflectivityof thecrust.
gases),combinedwith datafrom boreholeloggingprovidedthe
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
EMMERM•N AND LAUTERJUNG' KTB DEEP DRILL HOLE
18,201
basisfor an optimumbalancebetweenloggingandcoring,and
also gave the engineersrapid feedback in case of technical
problems.
A lesson learned while drillin• the vilot hole was that the
_
_
DallmeyerR, . D., W. Frankea, ndK. Weber(Eds.)P, re-PermianGeology of CentralatutWesternEurope,604 pp.,Springer-VerlaNge, w York,
1995.
DresenG, ., J. DuysterB, . St'OckherRt,. Wirth, andG. Zulauf,Quartz
project managementmust have a clearly defined chain of
ContinentaDleepDrillingProgramKTB,J. GeophysR.es.,thisissue
commandandresponsibilityandthatdecisionmakingmustgive ELEKTB Group,KTB and the electricalconductivitoyf the crust,J.
equal weight to the concernsof the geoscientistsand thoseof
GeophysR. es.,thisissue
the engineeringteam.Thereforethe go-aheadfor
the superdeep
EmmetmannR,., The KTB pilothole:Tectonicsettingt,echnicadl ataand firstresultsi,n TheGermanContinentaDl eepDrilling Program,edited
hole by the Ministry for Researchand Technology was byR. EmmetmananndJ. Wohlenberg52, 7-553,Springer-VerlaNge, w
conditionalon reorganizationof the projectmanagementT. he
York, 1989.
new, and ultimatelysuccessfulm, anagemenst chemeconsisted Emmetmann,R., and H.J. Behr, Location for the superdeepborehole
of three directorates: geoscience, borehole logging and experimentation,and engineering.The final decisionswere
confirmedT,ectomq•hysic1s3,9, 339-340,1987. EmmetmannR,., andJ. LauterjungD, oubleX-rayanalysisof cuttingsand
rock flour:A powerfultool for rapidand reliabledeterminatioonf
madeby a projectmanagerwith experiencein all threeareas, boreholelithostratigraphSyc,i.Drill., 1,269-282, 1990.
andhisresponsibilitywasto weightheoftendiverginginterests ERCEUGTGroupA, nelectricarlesistivitcyrustasl ectionfromtheAlpsto
of the threedirectorates.He was advisedby an expert panel theBalticSea(centraml gmenot f theEGT), Tectonophysic2s0,7, 123-
made up
from
leading scientistsand
industry representatives.
139, 1992.
FrapeS.K., andP.Fritz,Thechemistrayndisotopiccompositionf saline
This managemenst tructureintegratedindustryexperienceand groundwatefrsomtheCanadianShieldG, eochi•nC. osmochimAc. ta,
geoscienceconcernsat the decision-makinglevel, and it
48, 1617-1627, 1982.
ensureda balanceddistributionof financesand manpowerfor Harjes,H. P.,et at.,Originandnatureof crustarleflectionsR:esultsfrom
drilling, coring,logging,andthe boreholeexperiments.
integratesdeismicmeasuremenattstheKTB superdeedprillingsite,J.
In retrospectw, e believethatthe time givenfor the planning
GeophysR. es.,thisissue HuengesE, ., B. Enge.•r,J. Erzinger,W. Kesselsa,nd J. Ktick,The
phase(7 years) and the presite investigations(2 years) was permeablcerust:Geohydraulpicropertiedsownto 9100 m depthJ, .
necessaryand sufficient. For the purposeof site selection, GeophysR. es.,thisissue.
however,it wouldhavebeenbetterto havedrilled a technically simple, 2-3 km hole at each site instead of several shallow boreholes(< 500 m).
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
issue.
M611erP, ., et at., Paleo-andrecentfluidsin the uppercontinentaclrust-
AcknowlegmentsW. e are especiallyindebtedto R. Trumbullfor his
ResultsfrowntheGern•anContinentadl eepdrillingProgram(KTB), J.
constructivediscussionasndcritiqueof themanuscriptW. e alsothankU.
GeophysR. es.,thisissue.
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
O'Brien, P. J., J. Duyster,B. Grauert,W. SchreyerB, . St'0ckherta,nd K. Weber, Crustal evolutionof the KTB drill site:From oldestrelicsto the
lateHercyniangranitesJ,. GeophysR. es.,thisissue. Pechnig,R., G. Zimmermann,S. Haverkamp,J. Wohlenberg,and H.
BurckhardtI,ntegratedloginterpretatioin theGermanContinentadl eep
the scientificprogram(Em 23/14) and for supportingthe scientistsand
drilling Program:Lithology,porosity, and fracturezones,J. Geophys.
techniciansof the field laboratory(Em 23/19). Finally, specialthanksare due to the Universityof Giessenfor providingfacilitiesfor coordination of theprogramandadministrativesupportfor thefield laboratory.
Res., this issue Stoeckhert, B., The "brittle-ductile transition" in the KTB borehole: A
tentative prognosis,KTB Rep. 94-2, 25-34, Nieders,•ichsisches Landesdamftor BodenforschH.,annoverG, ermany,1994.
Stoll,J., J. BigalkeandE.W. Grabnet,Electrochemicmalodellingof self-
References
potentiaal nomaliesS, urv.Geophys.1, 6, 107-120,1995. Wagner,G. A., et al., Post-Variscatnhermalandtectonicevolutionof the
KTB siteanditssurroundingsJ,. GeophysR. es.,thisissue
Borm,G., B. EngeserB, . HoffersH, .K. Kutter,andC. Lempp,Borehole Zoback,M.D., andH.-P. Harjes,Injection-induceedarthquakeasndcrustal
instabilitiesin theKTB mainboreholeJ, . GeophysR. es.,thisissue.
stressat9 km depthattheKTB deepdrillingsite,GermanyJ, . Geophys.
Bosum,W., U. Casten,S.C. Fieberg,1. Heydr, and H.C. Soffel,Three-
Res., this issue
dimensionainlterpretatioonf theKTB gravityandmagneticanomalies,
J. GeophysR. es.,thisissue
Brudy,M., M.D. Zoback,K. Fuchs,F. Runm•el,andJ. Baumg'tirtner,
Estimationof the completestresstensorto 8 km depthin the KTB
R. Emmermannand J. Lauterjung,GeoForschungsZentmPmotsdam,
•ientific drill holes:hnplicationfsor crustalstrengthJ,. GeophysR. es., TelegrafenbergA17, D-14473 Potsdam,Germany. (e-mail: lau@gfz-
this issue
potsdam.de)
ByefleeJ,.D,,FrictionofrocksP, ureAppl.Geophys.,11661,5-629,1978.
Clauser,C., et at., The thermalregimeof thecrystallinecontinentaclrust: (ReceivedFebruary14, 1996;revisedDece•nber18, 1996;
ImplicationfrsomtheKTB,J. GeophysR.es.t,hisissue
acceptedDecember18, 1996.)