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Abstract Volume8th Swiss Geoscience MeetingFribourg, 19th – 20th November 2010
Department ofGeosciences
3. Himalayan Geology: A tribute to Augusto Gansser on his 100th anniversary
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Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
3.HimalayanGeology:AtributetoAugustoGansseronhis100thanniversary
Guido Schreurs, Neil Mancktelow, Ruedi Hänny, Jean-Pierre Burg
Swiss Tectonics Studies Group of the Swiss Geological Society Swiss Society of Mineralogy and Petrology
3.1 BaudA.:AgeologicalaccountofSouthTibet:1936Gansser’sdiarytotheholyKailas
3.2 DolatiA.,BernoulliD.,BurgJ.-P.,SmitJ.,MüllerC.,SpezzaferriS.,SergeyS.:SedimentologyandstratigraphyoftheMakranaccretionarywedgeinIran
3.3 DolatiA.,BurgJ.-P.,SmitJ.,BernoulliD.:StructuralanalysisofcentralMakranaccretionarywedge(SEIran)
3.4 Dolati A., SewardD., Smit J., Burg J.-P.: Tectonic evolution ofMakran accretionarywedge (SE Iran) using lowtemperaturethermochronologyandtectono-stratigraphicevidences
3.5 GrasemannB.:FoldgrowthintheZagrosfold-and-thrustbeltinKurdistan(NE-Iraq)
3.6 GrujicD.,WarrenC.J.,KellettD.A.,WoodenJ.L.:Syn-collisionalexhumationofthecontinentallowercrust
3.7 JalaliA., DolatiA.,BernoulliD.,BurgJ.-P.:PreliminaryresultsofCretaceous-EocenesedimentanalysisofMakranaccretionarywedgeinSEIran
3.8 MolnarP.:TheupwardandoutwardgrowthofnortheasternTibetandgeodynamicimplications
3.9 Monsef I., Rahgoshay M.: Compositional variations and geodynamic implications of the Mesozoic island arcmagmatismintheSanandaj-Sirjanarc-basinsystem
3.10 RahnM.,WangH.:MetamorphicanddenudationpatternsoftheSongpan-Garzêf lyschinSichuanProvince,China
3.11 RubattoD.,ChakrabortyS.,DasguptaS.:ProtractedmeltingintheHigherHimalayanCrystalline(Sikkim,India)
3.12 SteckA.,EpardJ.L.:StructuraldevelopmentoftheTsoMorariultrahighpressurenappeoftheLadakhHimalaya
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Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
3.1
AgeologicalaccountofSouthTibet:1936Gansser’sdiarytotheholyKailas.
BaudAymon
BGC, Parc de la Rouvraie 28, CH-1018 Lausanne ([email protected])
Asbrilliantlytoldinhisfamousbook“ThronderGötter”andreportedinthe“CentralHimalaya,GeologicalobservationsoftheSwissexpedition1936”,AugustGansser,stayingthenclosetotheTibetborder,grabbedhischanceoftwopilgrimsgoing to theKailasandhedecidedwithin fewhours to follow themand toenter in the forbiddenLand.Disguised inTibetanmonk,hisitinerarybroughthimthroughtheMangshangpasstotheRaksasvalleyand“daemon”lake.Thiswayleadhimtodiscoverawholechainofexoticmountains:theAmlang-laf lyschwithtwozonesofblocks,somesimilartothefamousKiogarExoticswithreefal,DachsteintypeTriassiclimestone,theothercalledtheChirchunExoticsofdeepwaterfacies(redTriassicammonoidlimestoneandradiolarites),bothtoppedbyathicksheetofperidotite(calledJungbwafromthenomadcampWesttheRaksaslake).ArrivingatthefootoftheholyKailaspeak,hewasagainsurprisedtofindthesamef lyschwithexoticblocksandperidotite,withsouthwarddippingtectoniccontact(GreatCounterthrust)withwhathecalledtheTranshimalayaKailasconglomerate.Ashehadtohidehiscamera,hammerandnotebookandtakecarewhencollectingandstoringsamples,thequalityandthesubtletyofhisobservationinsuchadverseenvironmentareastounding.Hisreportwithdrawings,panoramaandpicturesonSouthTibetgeologyin1939andinhisfamous“GeologyoftheHimalayas”book(1964),withalreadytheconceptoftheIndussuturezone,oflargesouthwardmovementsofoce-anicExoticthrustmassandthe“underthrustingoftheIndianshieldagainstTibetanmass”werereadytobeincorporatedandtogiveconvincingargumentsintotheplatetectonictheorythathasbeenexpoundedrespectivelythirty-oneandsixyearslater.
Now,ontheGansser’spanoramasectionoftheAmlang-la,thereareapparentlynonewdetailedreportsandwewillhavejusttolabelitasAmlang-laaccretionprismoverlainbyobducted(orsupra-subduction)Jungbwaophiolites.TheGansser’sIndussuturebecame“Indus-YaluSuturezone”thatseparatestheIndianblockfromtheLhasablock.AbouttheExoticblocksofthearea,theKiogarfaciescanbenowinterpretedasshallowTriassicoceanicisland(seamount)andtheChirchunfaciesiscorrespondingtoPermianseamounts.ItisonlythisyearthataTibetanPermian-TriassicsectionoftheChirchunFacieshasbeendescribedindetail.
Itisalsointerestingtonotethatduringhisfirstveryshorttwodays trip toPurang (Taklakot) in the forbidden land,AugustGanssernotonlyrecognizedthearchshapeofthe7700m.highGurlaMandhatabutobservingtiltingofter-rassesalongthemountainsideandthefresherosivemor-phology,hereportedthisveryrecent, incrediblehighup-doming.WeactuallyknowthattheGurlaMandhataispartoflargerecentextensionaldomesofgneissthatoccurnor-th the High Himalaya Range. Only recently, more thansixty years after Gansser’s report, detailed descriptionshavebeenpublishedandtheinterpretationoftectonicex-humationorerosion-drivenexhumationisnowsubjectoflargediscussions.The written geological accounts of August Gansser, ourgreatgeologicalfield-explorer,aremodelsofthegenreandremainofagreattopicality.
AugustGansserasaTibetanPilgrim(Heim,A&Gansser,A.,1938,
ThronderGötter,MorgatenVerlag,Zürich,f.72)
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Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
3.2
SedimentologyandstratigraphyoftheMakranaccretionarywedgeinIran
DolatiAsghar1,BernoulliDaniel1,BurgJean-Pierre1,SmitJeroen1,MüllerCarla2,SpezzaferriSilvia3&SergeySergeev4
1 Earth Sciences, ETH-Zurich, Sonneggstr. 5, CH-8092 Zurich ([email protected])2 6 bis r Haute 92500 RUEIL MALMAISON, France3 Department of Geosciences, University of Fribourg, ch du Musee 6, 1700 Fribourg4 Karpinskii All-Russia Research Institute of Geology (VSEGEI), Srednii pr. 74, St. Petersburg, 199026 Russia
TheMakranAccretionaryPrism(MAP)resultsfromtheconvergence,initiatedduringtheLateCretaceous,betweentheArabianandEurasianplates.TheactiveMAPhasgrownseawardsbyfrontalaccretionandunderplatingoftrench-fillse-dimentssincetheMiocene.Today,thesystemischaracterizedbyashallowdippingslab(<2°),greatsedimentthickness(>7km)intheforelandoftheOmanSeaandawedgewidthof>500km,>300kmofwhichareexposedonshore.
Newmapping and structural sections document the stratigraphic and structural developments of the centralMakranAccretionaryWedge (MAW) insouthernIran.Fourmaintectono-stratigraphicprovincesweredistinguished,whicharefromnorthtosouth:North-,Inner,OuterandCoastalMakran.NorthMakranisdominatedbymafictointermediateigne-ousrocks(FannujUnit)andtectonicmélangesinwhichigneousrocksandCretaceousdeep-watermarinesedimentsareinvolved (Maskutan). Locally, Upper Cretaceous shallow-water limestone unconformably covers deformed LowerCretaceoussedimentsandigneousrocks.ThefirstturbiditicsequencescontainingmaficfragmentsweredepositedduringtheLateCretaceous.Tothesouth,abovetheGhasrGhandThrust(InnerMakran),LowerEocenedeep-marinesedimentsandvolcanicrocksof thePipUnitgrade intothedeepermarineturbiditicsequencesof theEoceneTangSarhehUnit,whichshowsageneralthickening-andcoarsening-upwardtrend.Wellpreservednummulitids inturbiditicsandstonesand hundred meters across exotic blocks of Eocene shallow-water limestone in the Tortonian olistostrome indicateshallow-watercarbonatedepositionnorthoftheturbiditebasin.Theturbiditesbecomemoreterrigenousandproximal(channelized)duringEarly–LateOligocene,whichsuggestsprogradationof submarine fans (MarkanandPirdanUnits),followedbymoredistaldepositionduringtheLateOligocene(RaskUnit).Thepro-deltaturbiditesgradeup-sectionintoLowerMiocenesandstoneswhicharedepositedonashelfdominatedbywavesandtidalcurrents.TheLowerMiocenesediments,cropsoutinbothInnerandOuterMakran,aremainlymarlswithgypsum(GhasrGhandUnit)weredepositedinbasinswithrestrictedcirculation.Thesedepositsgradelaterally intobioclasticsandstonesandmarls (PishamakandRokshaUnits)andcorallimestones(VaziriUnit)borderingthebasin.Plantremainssuggestanemergingareatothenorth.MiddleMiocenesediments(PeersohrabUnit)cropoutmainlyinOuterMakran,betweentheGhasrGhandandChahKhanThrusts.HoweverthepassagefromtheLowertoMiddleMioceneisnotobservedbuttheMiddleMiocenesedimentstartswithdeep-marineturbiditetothesouthofGativanThrustwhichgradeup-sectionintoshallowerfacies.CoastalMakran,tothesouthofChahKhanThrust,exposessedimentsmostlyyoungerthantheLateMiocene.Thesesedimentsrepresentawedge-topbasinwithashallowing-upwardssequencefromslopemarlstocoastalandcontinentaldeposits.Allthepro-vinces,CoastalMakranexcepted,arecoveredunconformablybyalargeolistostromeincludinggiantblocksofigneousandsedimentaryrocksfromNorthMakranandofsedimentsfromInnerMakran.ThisolistostromewasemplacedduringtheTortonian(11.6–9.6Ma).
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Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
3.3
StructuralanalysisofcentralMakranaccretionarywedge(SEIran)
DolatiAsghar1,BurgJean-Pierre1,SmitJeroen1andBernoulliDaniel1
1 Earth Sciences, ETH-Zurich, Sonneggstr. 5, CH-8092 Zurich ([email protected])
TheMakranAccretionaryPrism(MAP)isformedbyactiveconvergencebetweentheEurasianandtheArabianplates.TheoceaniccrustoftheArabianplateissubductingtothenorthundertheEurasiancontinent,therebybuildingtheMAP.Thiswedgeischaracterizedbyashallowsubductionangle(<2°),greatsedimentthicknessontheOmanSeaandawedgewidthof>500km,whichmorethanhalfisexposedonshore.
NewmappingandstructuralsectionsdocumentthestructuraldevelopmentsofthecentralMakranAccretionaryWedge(MAW)insouthernIran.Fourmaintectonicunitsaredefined,whichfromnorthtosouthare:North-,Inner,OuterandCoastalMakran.Alltheseunitsaredelimitedbyregionalthrusts.Theuppermosttectonicunit,North-Makran,containsCretaceousrockswhichIngeneralcontainopenfoldswithwavelength(>200m)trendENE–WSW.TheunitisthrustovertheEoceneturbidites,exposedinInnerMakranbynorth-dippingBashakerdThrustandanImbricateZone.Towardsouth,Eocene-OligoceneturbiditescontainS-vergent,tighttoisoclinalfoldswithageneralWNW–ESEtrend.Incontrast,theMiocenesedimentscontaingentleandsymmetricalfoldswithlargewavelength(>500m)whichimpliesstraindifferences,strongerinpre-OligoceneandweakerinMiocenesediments.GrowthstratainMiddleMioceneturbiditesindicatefoldingandthrustingduringthistime.AllmajorfaultsareN-dippingthrustsassociatedwithf latandrampsystems.Accordingtothenewgeologicalmapandcrosssections,themaindécollementhasdevelopedinOligoceneshalelayers.TheGhasrGhandThrustbringstheInnerMakranonLower–MiddleMiocenesedimentsexposedinOuterMakran.Thesesedimentsarefoldedsymmetricallyandgentlywithlargewavelength(>500m)andtrendE–W.Usuallylargeboxfolds(wavelength>100 m) dominate this tectonic unit. Potential décollement horizons are Oligocene or Middle Miocene shales. TheN-dipping Chah Khan thrust separate Outer Makran in the north from Coastal Makran., which contains sedimentsyoungerthanUpperMiocene.Foldsaresymmetric,open-gentle,rounded-bluntwithverylongwavelength(>10km)andlowamplitudes.TheytrendE–W.Planarandbookshelfnormal faultscuttingsedimentsyounger thanUpperMiocenecharacterizethisunit.
CalculationofpaleostresstensorsindicateregionalNNE–SSWcompressionwhichisconsistentwithmappedfoldtrendsandmajorthrustsaswellaswiththepresentdayconvergencedirectionbetweentheArabianandIranianplates.TheseresultsclearlyshowastablestressfieldforthestructuraldevelopmentofMAWfromCretaceoustorecent.Extensioncharacterizesamorecomplexandtimelylessstablesystem.CoastalMakranrecordedregional,radialandactiveextensi-on.LocalextensionaleventsinNorth-Makranareaarelocalfeatureslikeinreleasingbendsofstrike-slipfaults.
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Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
3.4
TectonicevolutionofMakranaccretionarywedge(SEIran)usinglowtemperaturethermochronologyandtectono-stratigraphicevidences
AsgharDolati,Diane.Seward,Jeroen.SmitandJean-PierreBurg
Earth Sciences, ETH-Zurich, Sonneggstr. 5, CH-8092 Zurich ([email protected])
Low temperature thermochronology (apatite and zircon fission-track analysis) throughout the Makran AccretionaryWedgeprovidestemporalconstraints,thatcanbeinterpretedintermsofburialrelatedtobothsedimentaryandtectonicoverburdenand laterexhumation.Fissiontracks inapatitehosted inhorizonsranging inage fromLateCretaceous toMiocene(75-10Ma)haveallundergoneatleastpartialannealingsincesedimentation.Ageneralincreaseinannealingwithstratigraphicagereflects increasedtemperatures (burialdepth).Samplesfromhorizonsasyoungas10Maareslightlyreset implying that temperatures>60°Cwerereachedprior toeventualcoolingandexhumation;horizonsolder thanabout40Mahavereachedtemperaturesofalmost110°C,theclosuretemperatureofapatite.Fromthisdataandassocia-tedtectono-stratigraphicobservations,itispossibletomakesomeestimatesonthetimingofthrustactivity.Thereisaregional tendencyforsouthwardthrustpropagationovertime.Betweenabout27-20Matheolderhorizons (75-63Ma)fromthenorthernnappewerebeingexhumedwhileotherunitswerestillbeingdeposited.Theyoungestcooling/exhu-mationeventof10-7.9Maisrecordedinsedimentsofthefootwallnappes.Inaddition,timingofthrustactivityhasbeeninfluencedby theTortonian olistostrome. The apatite fission-track results suggest that the recent outcrops tookplaceaboveadécollement/décollementsatadepthofabout5-6kmconsideringageothermalgradientofca.20ºC/km.
Thefactthattheapatiteshavenotreachedfullannealinginmostplacesputsanupperlimitonthepaleo-temperaturereachedsuchthatthezirconsinglegrainagescanbeconsideredtorepresenttruedetritalages.Furtherconfirmationthattheyhavenotbeenresetisthatnosinglegrainzirconagesarelessthanthestratigraphicagefromtheenclosinghorizons.Lagtimesforindividualgrainsrangefromalmostzeroto500Ma.ThezircondatasuggestsvolcanicactivityfromLateCretaceoustoOligocenetimes.ItalsoconfirmstherecyclingofsedimentfromwithintheaccretionarywedgeduringtheMiocene,wherebysedimentfromthenorthernupthrustedunitswassuppliedtotheproximalbasins.
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Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
3.5
FoldgrowthintheZagrosfold-and-thrustbeltinKurdistan(NE-Iraq)
Grasemann,Bernhard
Department for Geodynamics and Sedimentology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria ([email protected])
Fold-growthmodelsinfold-and-thrustbeltsareofmajorscientificandeconomicinterestbecausetheyareestimatedtocontain14%oftheknownand15%oftheundiscoveredglobalrecoverablehydrocarbons.EspeciallytheZagrosfold-and-thrustbelt,containing49%ofglobalfold-and-thrustbeltrelatedhydrocarbonshasattractednumerousrecentstudies(e.g.Lacombetal.,2007andreferencescitedtherein).Whereasthoroughtectonicandgeomorphologicalinvestigationsfocus-edontheSEZagrosfold-and-thrustbeltintheIslamicRepublicofIran,considerablylessmodernstudiesinvestigatedtheNWpartsintheParliamentaryRepublicIraq.
TheZagrosFoldBeltisthenortheasterncontinuationoftheArabianPlatform,wherethenorthtrendingOmanlineter-minatesitssoutheasternextension(Gansser1955).TheZagrosMountainsstartedtoformasaresultofthecollisionbet-weentheEurasianandArabianPlates,whoseconvergencebeganintheLateCretaceousaspartoftheAlpine–Himalayanorogenicsystem.Geodeticandseismologicaldatadocumentthatbothplatesarestillconvergingandthatthefold-and-thrustbeltoftheZagrosisactivelygrowing(Gansser,1969).Relationshipsbetweenactivetectonicsanderosionalland-formsrevealdifferencesinthetypeandratesofdeformationandfoldgrow(Ramseyetal.2008).Theevolutionandchan-gesindrainagepatternsaswellastheinfluenceoffoldgrowthtotheirappearanceareevidenceforthekinematicsoffoldsandfaults.Tributarynetworksactverysensitivetodeformationandthereforegeneratecharacteristicgeomorpholo-gicshapesthatcanbeusedfortheinterpretationoftectonicprocesses(Burbank&Anderson,2001).
BymeansofstructuralfieldworkandquantitativegeomorphologicaltechniquestheprogressivefoldgrowthofanticlineslocatedintheNEofthecityofErbilintheKurdistanregionofNorthernIraqwereinvestigated.ThispartoftheZagrosfold-and-thrustbelt isdominatedbyopenfoldingwithwavelengthsofabout10km.Themechanicalanisotropyoftheformationsconsistingofasuccessionofrelativelycompetent(massivedolomiteandlimestone)andincompetent(claysto-neandsiltstone)sedimentsessentiallycontrolsthedeformationpatternwithopentogentleparallelfoldingofthecom-petentlayersandf lexuralf lowfoldingoftheincompetentlayers.
Theanticlineshavenotdevelopedfromsubcylindricalembryonicfoldsbuttheyhavemergedfromdifferentfoldsegmentsthatjoinedlaterallyduringfoldamplification.Thisfoldsegmentswithlengthbetween5and25kmhavebeendetectedbymappingancientandmodernrivercourses that initiallycut thenoseofgrowing foldsandeventuallygotdefeatedleavingbehindawindgap.Foldsegments,propagatingindifferentdirectionsforceriverstojoinresultinginsteepgorges,whichdissectthemergingfoldnoses.Geomorphologicalindicesofthedrainagebasins(spacingandelongationratio,cir-cularityindexandshapefactor)ofdifferentpartsintheforeandback-limboftheanticlinesdemonstratethatthebasinshavealowmaturityandthatfoldgrowthisstillhighlyactivity.
REFERENCESBurbank,D.&Anderson,R.S.2001.TectonicGeomorphology.BlackwellScienceIncMalden.Gansser,A.1955.NewaspectofthegeologyoftheCentralIran.3eCongr.mond.Pétrole,Actesetdoc.,1,279-300.Roma.Gansser,A.1969:ThelargeearthquakesofIranandtheirgeologicalframe.EclogaeGeologicaeHelvetiae,62,2,443-466.Lacombe,O.,Lavé,J.,Roure,F.&Verges,J.2007:ThrustBeltsandForelandBasins:FromFoldKinematicstoHydrocarbon
SystemsSeries.Springer,BerlinHeidelbergNewYork.Ramsey,L.A.,Walker,R.T.&Jackson,J.2008.FoldevolutionanddrainagedevelopmentintheZagrosmountainsofFars
province,SEIran.BasinResearch,20,23-48.
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Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
3.6
Syn-collisionalexhumationofthecontinentallowercrust
GrujicDjordje1,WarrenClareJ.2,KellettDawnA.1&WoodenJosephL.3
1 Dalhousie University, Department of Earth Sciences, Halifax, NS B3H 4J1, Canada ([email protected])2 The Open University, Earth and Environmental Sciences, Milton Keynes, MK7 6AA, United Kingdom3 Department of Geological and Environmental Science, Stanford University, Stanford, USA
HerewepresentatectonicmodelfortheevolutionoftheeasternHimalayaandsuggestageneralmodelforlateorogenicexhumationofthelowercontinentalcrust.
MaficandpeliticgranulitesexposedintheeasternHimalayankingdomofBhutanpreservetexturalevidenceforaprecur-sorhigh-pressuremetamorphicevent,thepreciseconditionsofwhicharegenerallyunrecoverableduetothelaterhightemperatureoverprint.AshighpressuremetamorphismisrareintheHimalayas,especiallyintheeasternpartsoftheorogen,theirthermobarometricalandgeochronologicalevolutionplaceimportantconstraintsonthegeodynamicevolu-tionoftheHimalayainparticularandcontinentalcollisionsingeneral.WereportSHRIMPtraceelement(REE)andU–Pbzircon,andLA-ICPMSU-Th-Pbmonazitegeochronologicaldata.Combined,thesedatasuggestthatzirconscrystallizedat14-15Maoveratemperaturerangeofca.705-815°C.ThisageisinterpretedtoindicatethetimingofHPmetamorphismduetothelackofnegativeEuanomaly,thedepletedheavyREEsignatureandthelowtemperaturesofcrystallization.Monazites associated with sillimanite-grade metamorphism in granulite-hosting garnet-sillimanite-biotite migmatiticgneissesyieldrimagesbetween15.4±0.8Maand13.5±0.5Ma.Theserocksstructurallyoverlieolder21-16Magarnet-sillimanite-biotitemigmatiticgneissesinwhichgranulite-faciesmaterialisabsent.Thegeochronological,petrologicalandstructuraldatasuggestthatanout-ofsequencethrustlikelyseparatesthetwopackages.ThesedataareconsistentwithexhumationofGHSmaterialfromavarietyofcrustaldepthsatdifferenttimesalongtheHimalayanorogenduringtheMiocene. Exhumationofeclogitesandgranulites inBhutanwaspossiblydrivenby tectonic forcingoveran incomingIndiancrustalramp.
3.7
PreliminaryresultsofCretaceous-EocenesedimentanalysisofMakranaccretionarywedgeinSEIran
AliJalali1,2,AsgharDolati1,DanielBernoulli1,Jean-PierreBurg1
1 Earth Sciences, ETH-Zurich, Sonneggstr. 5, CH-8092 Zurich ([email protected])2 Geological Survey of Iran, Meraj Avn., Azadi Sq., Tehran, Iran. Po. Box 13185-1494
UpperCretaceoustoMiocenesedimentsoftheMakranaccretionarywedgearedominatedbybouma-typeturbiditesand-stonesandshales.
Havingspecifiedthestratigraphicagesofthesuccessivelithostratigraphicfacies,thisstudyconcentratesonthesourceofthesediments.TheheavymineralanalysesoftheCretaceousturbiditesindicatescontributionofophiolitefragmentsex-posednot far fromthe studiedbasin, as suggestedby theangular shapeof clastic fragments.The likely source is theMakranophiolitesthatcropoutalongthenorthernboundaryoftheMakranaccretionarywedge.FissiontrackagesofzirconinCretaceoussandstonesshowtwomainpopulations,oneat77±6Maandoneat144±10Ma.Thesetwoageclustersdefiningtwodifferentsources.
PetrographicstudiesofEoceneturbiditesidentifiedNa-andK-idiomorphicfeldsparsaswellassanidineminerals,whichalltogethersuggestsilicicvolcanicsources.TheEoceneturbiditesalsocontainophioliticfragments,similartothosefoundintheCretaceoussediments.Eocenepolymictic,conglomeratescontainultramafic,maficandgranitepebbles.The86.2±10.6 and 88.4± 12.0 Ma zircon fission track ages of granite pebbles point to plutonic source rocks older than LateCretaceous.Sincethesizesofthepebblesarelarge(10-50cm),thesourceisnotasfarastheHimalayas.AclosersolutionwouldbetheSanandaj-Sirjanplutonicbelt,locatedjustN–NWofthewedge.
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Platform Geosciences, Swiss Academy of Science, SCNATSwiss Geoscience Meeting 2010
3.8
TheupwardandoutwardgrowthofnortheasternTibetandgeodynamicimplications
MolnarP.
Department of Geological Sciences and Cooperative Institute for Research in Environmental Science (CIRES), University of Colorado, Boulder, Colorado USA, 80309-0399 (CO, USA) ([email protected])
Severalrecentstudies fromnorthernTibetdemonstratethat faulting, folding,rapidexhumation,androtationaroundverticalaxesoccurredshortlyafter IndiacollidedwithsouthernEurasiaat45-50Ma;manyotherrecentstudiesshowenhanceddeformationonthemarginsofTibetandinsurroundingregionsbeginningsince~15-10Ma.ThefirstimpliesthattheessentiallyalloftherocknowcomprisingTibetwas, immediatelyaftercollision,partofwhatgrewtobetheTibetanPlateauandthatastheplateaugrewhigher,itsnorth-southdimensiondecreased.Thus,anynorthwardpropaga-tionofdeformationasIndiapenetratedEurasiawassuperimposedonthisplateau-widecontraction.ThepresenceofastrongTarimBasinandNorthChinacraton,andperhapsofastrongQaidamBasin,helpedtoconcentratedeformationonitsmarginsandthereforetoconfinethedimensionsofTibet.Thedeformationbeginningnear15-10Maincludesnotonlyanaccelerationofcrustalshorteningonthemarginsoftheplateau,butalsoachangeintheorientationofcompressionalstraininnortheastTibetfromNNE-SSWtomorenearlyENE-WSWwithanimportantcomponentofleft-lateralshearonE-Wplanes.ThischangemightberelatedtoremovalofmantlelithospherefrombeneathnorthernTibet.Present-daydeformationofnortheasternTibetincludesthrustfaultingonnumerousESE-WNW-trendingfaultsandbothright-andleft-lateralsliponconjugatestrike-slipfaults.Ifthisdeformationfieldistobedescribedintermsofrelativemovementsofcrustalblocks,manytensofblockswillbeneededtosuchadescription,whichmakessuchadescriptionvirtuallyuse-lessforunderstandingthedynamicprocesses.
3.9
CompositionalvariationsandgeodynamicimplicationsoftheMesozoicislandarcmagmatismintheSanandaj-Sirjanarc-basinsystem
MonsefIman1&RahgoshayMohamad1
1ShahidBeheshtiUniversity,EarthSciencesFaculty,Tehran,Iran([email protected])
ThesubductionoftheNeo-TethysoceanappearstohaveinitiatedinthesouthoftheSanandaj-Sirjanarc-basinsystematEarly Jurassic to Late Cretaceous time in Iranian convergent margin environment. These magmatic activities in theSanandaj-Sirjanmagmaticarcshowsignificantgeochemicalvariationsduringtheirevolutionalperiod.ThesemagmaticsequenceshaveexposedwithMesozoicageinmagmatic-sedimentary-turbiditicstructuralzonealonga1300kmarc-basinsystem.
Thegeochemicaldatasuggestmagmaticevolutionfromthetholeiitictothecalc-alkalinecharacteristicsinspaceandtime.REEandtraceelementpatternsshowmoderatetohighLREE/HREEratios,lowtomoderatedepletioninNbrelativetoYb,andhighTh/YbratiosrelativetoMORBandWPB.TheparentmagmaofEarlytoLateJurassicsequences,withislandarctholeiite(IAT)compositions,hasbeenoriginatedfromthespinellherzolitemantlewithprimitivemantle(PM)compositi-on,witheffectiveofliquidsandsedimentresultedfromthesubductingslab.TheparentmagmaofCretaceoussequenceswith island arc tholeiite to E-MORB compositions have been resulted from the garnet - spinel lherzolitemantlewithE-MORBtoOIBcomposition.
Thesecompositionalchangesmayberelatedtohighsedimentandhydrothermalf luxes,resultedfromthedeepsubductedslabintothemantlewedge.ThesemagmaticsequencesareoriginatedduringthenortheastwardsubductionoftheNeo-TethyanoceanplateundertheSanandaj-Sirjanarcbasinsystem,duringtheEarlyJurassictoLateCretaceoustime,intheislandarctectonicenvironment.Thearc-trenchsystemcollidedwiththeArabianpassivemargininthelateCretaceousalongtheMainZagrosThrustBelt.TheZagrosorogenisayoungTertiarycollisionbeltgenerallyconsideredarecentana-logueoftheAlpine-Himalayanorogenicsystem.
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Figure1.SatelliteimageofstructuralsketchmapofIran.ThelocationsofmajorstructuralzonesconsistingofSanandaj-SirjanArc-
BasinSystem,CentralIranianBlock,AlborzZone,KopedaghZone,MakranZone,ArabianPlatform,ZagrosFoldedBeltandHelmand
Blockareindicated.
REFERENCESPearce, J.A.&Parkinson, I.J. 1993:Traceelementmodels formantlemelting: application tovolcanicarcpetrogenesis.
GeologicalSociety,London,SpecialPublications,373-403.Pearce, J.A., Stern, R.J., Bloomer, S.H. & Fryer P. 2005: Geochemicalmapping of theMariana arc-basin system:
Implicationsforthenatureanddistributionofsubductioncomponents.Geochemistry,Geophysics,Geosystems,6,7,1-27.
3.10
MetamorphicanddenudationpatternsoftheSongpan-GarzêflyschinSichuanProvince,China
RahnMeinert1&WangHejing2
1 Swiss Federal Nuclear Safety Inspectorate ([email protected])2 School of Earth and Space Sciences, Peking University, Beijing 100871, P. R. China
ExhumationoftheQinglinandDabieShanorogensfromdeepcrustallevelsintheTriassicledtotheformationoflargesedimentarydepositsnorthandsouthoftheseorogens.Thebasinswerefilledwithupto10kmthickf lyschsequences(Songpan-Garzêf lysch,Ingersolletal.,2003)thatlaterunderwentshorteningandfolding(Rogeretal.2010)inanaccre-tionarywedgesetting.Thef lyscheswereoverprintedbetweendiagenetictolow-grademetamorphicgrade(Wangetal.2008).Exhumationofthef lyschunitswasdecoupledfromthesurroundingareas(e.g.theRedBasin,Richardsonetal.2008)bytwoextendedandactivefaultlines,theXianxuihefaulttothesouthwestandtheLongmenshanfaulttothesou-theast.Today,theSongpan-GarzêorogenformstheeasternmarginoftheTibetanplateau.
Themetamorphicpattern(mostlybasedonilliteandchloritecrystallinities)isinpartinfluencedbylocalizedexhumationalongtheLongmenshanfault.Metamorphicboundariescutacrosslarge-scaleTriassicfoldstructures.Fromthemetamor-
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phicparametersitisevidentthattheLongmenshanfaultsystemhasaccommodatedmorethan5kmofpost-metamorphicverticaldisplacement,whilefortheXianxiuhefault60kmofsinistralstrike-slipistobepostulated.
Fissiontrackdatafrom48samplescollectedwithinthef lyschesandalongaprofileacrosstheLongmenshanfaultsystemvarybetween3and136MaandindicateyoungandfastexhumationofunitsNWoftheLongmenshanfault.AgesbecomeolderwithincreasingdistancefromthefaultandreachaplateauofLower/UpperCretaceousvaluesfaraway.Itisshownby thermochronologicalmodelling thatmost ages can be shown to be the result of two thermal event, i.e. a LowerCretaceouscoolingepisode(140-90Ma)andalatereheatingandcoolingeventataround20-15Ma.StrongeffectsofalatecoolingeventarealsofoundfarawayfromtheLongmenshanfaultinareasofhighestmetamorphicoverprint.ItisthusconcludedthatthemetamorphicpatternasmappedatthesurfacetodayismarkedlyinfluencedbyexhumationprocessesalongtheLongmenshanfaultbutalsoalongf lysch-internalstructures.ThefindingsofastrongCretaceouscoolingeventcontrastswiththesynthesisofRogeretal.(2010)whodescribetheJurassicandCretaceousasaperiodoftectonicquie-scence.
REFERENCESIngersoll,R.V.,Dickinson,W.R.&Graham,S.A.2003:Remnant-oceansubmarine fans:Largest sedimentarysystemson
Earth.GSASpecialPaper370,191–208.Richardson,N.Y.,Densmore,A.L.,Seward,D.,Wipf,M.,Li,Y.,Ellis,M.A.&Zhang, Y. 2008: Extraordinary denudation in the SichuanBasin: Insights from low-temperature thermochronology
adjacenttotheeasternmarginoftheTibetanPlateau.JGR113,doi:10.1029/2006JB004739.Roger,F.,Jolivet,M.&Malavieille,J.2010:ThetectonicevolutionoftheSongpan-Garzê(NorthTibet)andadjacentareas
fromProterozoictoPresent:Asynthesis.JournalofAsianEarthSciences39,254-269.WangH.,Rahn,M., TAO,X., Zheng,N.&Xu, T. 2008:Diagenesis andmetamorphismofTriassic Flysch alongprofile
Zoige-Lushan,NorthwestSichuan,China.ActaGeologicaSinica82,917–926.
3.11
ProtractedmeltingintheHigherHimalayanCrystalline(Sikkim,India)
DanielaRubatto1,2,SumitChakraborty3,SomnathDasgupta4
1 Research School of Earth Sciences, The Australian National University, Mills Road, Canberra 0200, Australia ([email protected]) 2 Present address: Institute of Mineralogy and Geochemistry, University of Lausanne, Antrophole, CH-1015 Lausanne, Switzerland3 Institut fuer Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany 4 National Centre of Experimental Mineralogy & Petrology, University of Allahabad, 14 Chatham Lines, Bank Road, Allahabad-211002, Uttar Pradesh, India
Partialmeltingofthecontinentalcrustcommonlyoccursinorogenicsettingsattherootofmountainbelts.Thetimingofmeltinghassignificantimplicationsforthesecularevolutionoftheplanetintermsofmodelingoforogenicprocesses,heattransferandrheologyofthecrust.OneofthemostspectacularandcompletemigmatitesequenceisexposedintheSikkimValleyoftheeasternHimalayaswheretheLesserHimalayanCrystallineinthesouthandtheHigherHimalayanCrystalline inthenorth,bothreachedmeltingconditions.TheLHCconsistsofan invertedsequenceofgreenschist- toamphibolitegrademetapelites,whichreachedmuscovite-meltingconditions(~675°Cand7.5kbar,Dasguptaetal.2009).IntheHHCasimilarmetapeliticsequenceunderwentpervasivepartialmeltingathighergrade(~800°Cand7-12kbar).Thisfertilebulkcompositioncrossesaseriesofmeltingreactionduringtheprogradepathincludingparagonitemelting,f luidinducedmelting,muscovitemeltingandbiotitemelting.
Zirconandmonazite crystals innumerous leucosomesandmesosomes fromtheHHCshowmultiplegrowthdomains(Figure1).Thesedomainswereanalysedbymicrobeamforage(SHRIMP)andtraceelementcomposition(LA-ICPMS)inanattempttorelateagestoconditionsofformation.
Monazitepreservesthebestrecordofmetamorphism.Inmostsamplesmonaziteyieldtwoages,whichgenerallycorres-pondtodomainswithdifferentzoningpatternandcomposition.Intwomonazitesamplesanthird,olderagecomponentispresent.Zoningandtraceelementcomposition indicatethat initialmonazitegrowthoccurredatamphibolite faciesconditions,likelybeforetheonsetofmelting.Monazitegrowthinthepresenceofmeltwaswidespreadanddiachronousacrosssamples(29-17Ma).
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Zirconwasgenerallylessreactivethanmonazitetometamorphism.Alimitednumberofsamplespreserveuptotwodis-tinctgrowthzones,thatforshape,zoningpatternandcompositioncanbeattributedtomelting.Asformonazite, thetraceelementcompositionof thedistinctzircongrowthzones indicates that theywereproducedbydifferentmeltingreactions.Alsoforzircon,agesarediachronousacrosssamplesandvaryfrom~32to17Ma.
ThespreadofagesindicatesthatmeltingcontinuedacrosstheHHCformorethan10-15Maviaaseriesofmeltingreac-tions.Theepisodicrecordofeachsamplealsosuggeststhat,withinthistimewindow,zirconandmonazitecrystallizationfromthemeltwasdiachronouswithinandacrosssamples.Atrendtoyoungerages isobservedwithintheHHCfromnorth(SouthTibetanDetachmentside)tosouth(MainCentralThrustside).
Figure1.Backscatteredelectron(aandb)andcathodoluminescence(candd)imagesofmonaziteandzirconcrystals,respectively.The
crystalsshowmultiplegrowthzonesthatyielddistinctagestestifyingtoprotractedmetamorphismandmelting.Thecirclesindicate
thelocationofSHRIMPanalyses.Thescalebaris2µm.
REFERENCESDasgupta, S., Chakraborty, S.&Neogi, S. 2009: Petrologyof an invertedBarrovian sequenceofmetapelites in Sikkim
Himalaya,India:constraintsonthetectonicinversion.AmericanJournalofScience,309,43-84.
3.12
StructuraldevelopmentoftheTsoMorariultrahighpressurenappeoftheLadakhHimalaya
AlbrechtSteck1andJean-LucEpard2
*InstitutdeMinéralogieetGéochimie,UniversitédeLausanne,Anthropole,CH-1015Lausanne,Switzerland.E-mail:[email protected]**InstitutdeGéolgieetPaléontologie,UniversitédeLausanne,Anthropole,CH-1015Lausanne,Switzerland.E-mail:[email protected]
AsubductionandmultistageexhumationprocessfortheTsoMorariultrahighpressurenappeisdiscussed.Themodelisconstrainedbyareviewofpublishedthermo-barometricandagedatacombinedwithanewgeologicalandtectonicmapaswellasobservationsonthestructuralandmetamorphicevolutionoftheTsoMorariareaandtheNorthHimalayannappes.Aftercontinentalcollisionsome55Maago,theNIndiancontinentalcrustwassubductedtoadepthofover90kmbelowAsia.TheunderthrustingwasaccompaniedbythedetachmentandaccretionoftheuppercrustLateProterozoictoEarlyEocenesediments,creatingtheNHimalayanaccretionarywedge,infrontoftheactiveAsianmarginandthe103-50MaLadakharcbatholith.Atadepthofover90km,pressuresofover27kbarsandtemperaturesof500to600°C,thebasicdikesintheOrdovicianTsoMorarigraniteweretransformedtoeclogiteswithcrystallisationofcoesite,some53Maago.ThedetachmentandextrusionofthelowdensityTsoMorarinappe,composedof70%oftheTsoMorarigraniteand30%ofgraywackeswithsomeeclogiticdikes,occurredbyductilepureandsimplesheardeformation,pushedbybuoyan-cyforcesandbysqueezingbetweentheunderthrustedIndianlithosphereandtheAsianmantlewedge.TheextrudingTso
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Morarinappereachedadepthof35kmatthebaseoftheNHimalayanaccretionarywedgesome48Maago,wherethewholenappestackrecrystallizedunderamphibolitefaciesconditionsofaBarrovianregionalmetamorphism,withame-tamorphicfieldgradientof20°C/km.AnintenseschistositywithaW-EorientedstretchinglineationL1andtop-to-theEshearcriteriaandcrystallisationoforientedsillimaniteneedlesafterkyanite,testifytothephaseoftheTsoMorarinappeextrusionandpressuredrop.ReachingthebaseoftheNHimalayanaccretionarywedge,thewholenappestackcomposedfrombasetotopoftheTsoMorari,Tetraogal,KarzokandMata–Nyimaling-Tsarapnappes,wasoverprintedbynewschis-tositieswithafirstN-directedandasecondNE-directedstretchinglineationL2andL3,characterisedbytop-to-theSandSWshearcriteria.ThisstructuraloverprintwasrelatedtoanearlyN-andayoungerNE-directedunderthrustingoftheIndianplatebelowAsia,thatwasaccompaniedbyananticlockwiserotationofIndia.ThewarpingoftheTsoMoraridomestartedalreadysome48Maagowiththeformationofanextrudingnappeatdepth.TheTsoMoraridomereachedadepthof15kmsome40MaagointheeasternKiagarLaregionand30MaagointhewesternNuruchanregion.Theextrusionratewasofabout3cm/yrbetween53-48Ma,followedbyanupliftrateof1.2mm/yrbetween48and30Maandonly0.5mm/yrsince30Ma.ObservationsonthegeomorphologyshowthattheTsoMoraridomeisstillaffectedbyfaults,openregionaldomeandbasinandpull-apartstructures,inazoneofactivedextraltranspressionparalleltotheIndusSuturezone.
Figure1.StructuralmodelfortheemplacementoftheTsoMorarinappe.
REFERENCESDeSigoyer,J.,Chavagnac,V.,Blichert-Toft,J.,Villa,I.M.,Luais,P.,Guillot,S.,Cosca,M.,MascleG.,2000:DatingtheIndian
continental subduction and collisional thickening in thenorthwestHimalaya:Multchronology of theTsoMorarieclogites.Geology28,487-490.
Epard,J.L.,SteckA.,2008:StructuraldevelopmentoftheTsoMorariultra-highpressurenappeoftheLadakhHimalaya.Tectonophysics451,242-264.
Girard,M.Bussy, F., 1999: Late Pan-Africanmagmatism in theHimalaya:newgeochronological andgeochemical datafrom the Ordovician Tso Morari metagranites (Ladakh, NW India). Schweizerische Mineralogische undPetrographischeMitteilungen79,399-417.
Leech,M.L., Sing, S., Jain, A.K., Klemperer, R.M.,Manickavasagam, R.M., 2005: The onset of India-Asia conzinentalcollision:Early,steepsubductionrequiredbythetimingofUHPmetamorphisminthewesternHimalaya,EarthandPlanetarySciencesLetters234,83-87.
Schlup,M.,Carter,A.,Cosca,M.,Steck,A.,2003:ExhumationhistoryoftheeasternLadakhrevealedby40Ar/39Arandfissiontrackages:TheIndusriver-TsoMoraritransect,NWHimalaya.JournalofthegeologicalScietyofLondon160,385-399.
Schlup,M.,Steck,A.,Carter,A.,Cosca,M.,Epard,J-L.,Hunziker,J.,2010:ExhumationhistoryoftheNWIndianHimalayarevealedbysissiontrackand40Ar/39Arages.JournalofAsianEarthSciences,inpress.
