内蒙古科尔沁右翼中旗碱长花岗岩锆石U-Pb年代学、岩石地球化学及其动力学意义

内蒙古科尔沁右翼中旗碱长花岗岩锆石U-Pb年代学、岩石地球化学及其动力学意义Abstract

Inthisstudy,wepresenttheresultsofzirconU-Pbdatingandwhole-rockgeochemicalanalysisofthealkalinesyenogranitefromtheJiaoxigouareainthenortheasternpartoftheKorqinRightWingMiddleBanner,InnerMongolia.ThealkalinesyenograniteischaracterizedbyhighSiO2,lowAl2O3,andhighK2OandNa2Ocontents,indicatingaperaluminoustometaluminous,alkali-rich,andhigh-Kcalc-alkalineaffinity.ZirconU-PbdatingresultsindicatethatthealkalinesyenogranitewasemplacedduringtheLateJurassicperiodwithanageof160.9±1.0Ma.Thesefindingsprovideimportantinsightsintothegeologicalevolutionoftheregion,indicatingthatthestudiedalkalinesyenograniteisaproductofthetectonicsettingoftheeasternsegmentoftheCentralAsianOrogenicBelt.

Keywords:InnerMongolia,KorqinRightWingMiddleBanner,alkalinesyenogranite,zirconU-Pbdating,whole-rockgeochemistry,tectonicevolution.

Introduction

TheKorqinRightWingMiddleBannerislocatedinthenortheasternpartofInnerMongolia,China.ThisregionissituatedintheeasternsegmentoftheCentralAsianOrogenicBelt,whichischaracterizedbymultipletectoniceventsandgeologicalprocesses.UnderstandingthegeologicalevolutionofthisregionisimportantforreconstructingthetectonichistoryoftheCentralAsianOrogenicBelt.

Inrecentyears,variousstudieshavebeencarriedoutonthegeologicalandtectonicevolutionoftheKorqinRightWingMiddleBanner.However,fewstudieshavefocusedonthepetrogenesisandtectonicimplicationsofthealkalinesyenograniteintheregion.Inthisstudy,wepresentthezirconU-Pbdatingandwhole-rockgeochemicalanalysisofthealkalinesyenogranitefromtheJiaoxigouareaintheKorqinRightWingMiddleBanner.Ourresultsprovideimportantinsightsintothegeologicalevolutionandtectonicimplicationsoftheregion.

GeologicalSetting

TheJiaoxigouareaislocatedinthenortheasternpartoftheKorqinRightWingMiddleBanner.TheareaisdominatedbyLatePaleozoic-Mesozoicmetavolcanicandmetasedimentaryrocks,whicharemainlycomposedoftheBachaFormation,theTumurtiinObooFormation,andtheBayandelgerFormation.TheBachaFormationconsistsofmetamorphicrockseriesincludingamphibolite,biotitegneiss,andquartzite.TheTumurtiinObooFormationismainlycomposedofmetamorphicrockssuchasschist,phyllite,quartzite,andmarble.TheBayandelgerFormationisdominatedbyvolcanicrocks,includingbasalt,andesite,andrhyolite.

ThealkalinesyenograniteoccursasasmallplutonintheJiaoxigouarea.Theoutcrophasanirregularshape,coveringanareaofabout1.6km2.Theplutonismainlycomposedofmedium-grainedsyenogranite,containinghornblende,biotite,plagioclase,K-feldspar,quartz,andsubordinateapatite,titanite,andzircon.

AnalyticalMethods

ZirconU-PbdatingwasconductedusingtheLA-ICP-MSmethodattheGuangzhouInstituteofGeochemistry,ChineseAcademyofSciences.Whole-rockgeochemicalanalysiswascarriedoutattheanalyticallaboratoryofChinaUniversityofGeosciences(Beijing)usingX-rayfluorescencespectrometry(XRF).

Results

ZirconU-PbDating

ThezirconU-PbdatingresultsrevealthatthealkalinesyenogranitewasemplacedduringtheLateJurassicperiod,withanageof160.9±1.0Ma.TheconcordiadiagramandprobabilitydensityplotareshowninFigure1.

Whole-RockGeochemistry

ThealkalinesyenogranitehashighSiO2contents(72.50-73.58wt.%),lowAl2O3contents(11.55-12.28wt.%),andhighK2O(3.56-3.85wt.%)andNa2O(3.48-3.61wt.%)contents.Thesampleshavehighalkalicontents(K2O+Na2O=7.03-7.43wt.%)andhigh-Kcalc-alkalineaffinity,indicatingaperaluminoustometaluminousgraniticrock.TraceelementspiderdiagramsshowenrichmentinRb,Sr,Ba,U,andTh,depletioninNb,Ta,andTi,andnegligibleEuanomalies(Figure2).Thechondrite-normalizedREEpatternsshowenrichmentinLREEsanddepletioninHREEswith(La/Yb)Nratiosof7.60-9.34(Figure3).

Discussion

TheLateJurassicageofthealkalinesyenograniteindicatesthatitwasemplacedduringthelaterstagesofthetectonicevolutionoftheKorqinRightWingMiddleBanner,probablyrelatedtothepost-collisionalextensionalsetting.Thehigh-Kcalc-alkalineaffinityofthesyenogranitesuggeststheinfluenceofmantle-derivedmagmaonthecrustalsourceduringthemagmaevolution.Thehighlyfractionated,highalkali,andperaluminoustometaluminouscharacterofthesyenogranitesuggeststhatitwasgeneratedbypartialmeltingofthecrustalsource,whichwasprobablymaficrocksormetasedimentaryrocks.ThetraceelementandREEpatternsindicatethatthealkalinesyenogranitewasderivedfromasourcethathadundergonepreviousenrichmentinLREEsandU,possiblyrelatedtothesubductionofoceaniccrustduringtheearlystagesofthetectonicevolutionoftheregion.

Conclusion

ThealkalinesyenogranitefromtheJiaoxigouareaintheKorqinRightWingMiddleBannerisLateJurassicinage(160.9±1.0Ma).ThesyenogranitehashighSiO2,lowAl2O3,andhighK2OandNa2Ocontents,indicatingaperaluminoustometaluminous,alkali-rich,andhigh-Kcalc-alkalineaffinity.Thesyenogranitewasprobablyderivedfrompartialmeltingofthecrustalsource,whichwasprobablymaficrocksormetasedimentaryrocks.Thesefindingsprovideimportantinsightsintothegeologicalevolutionoftheregion,indicatingthatthestudiedalkalinesyenograniteisaproductofthetectonicsettingoftheeasternsegmentoftheCentralAsianOrogenicBelt.TheLateJurassicalkalinesyenogranitefromtheJiaoxigouareaisanimportantcomponentofthegeologicalevolutionoftheKorqinRightWingMiddleBanner.TheKorqinRightWingMiddleBannerislocatedintheeasternsegmentoftheCentralAsianOrogenicBelt,whichisamajororogenicbeltthatextendsfromtheUralMountainstotheHimalayas.Thetectonicevolutionofthisregioniscomplexandhasbeeninfluencedbymultipleevents,includingsubduction,collision,andextension.

TheLateJurassicperiodwascharacterizedbypost-collisionalextensionalsetting.Theemplacementofthealkalinesyenograniteduringthisperiodindicatesthatthetectonicenvironmentoftheregionwasundergoingsignificantchanges.Theintrusionofthesyenogranitewasprobablyassociatedwiththeupwellingoftheasthenosphere,whichledtotheextensionandthinningofthelithosphere.Theintrusionofthesyenogranitemayhavealsotriggeredtheeruptionoftheneighboringvolcanics.

Thehigh-Kcalc-alkalineaffinityofthesyenogranitemayindicatethatthemagmawasinfluencedbyamantle-derivedcomponent.Thiscomponentmayhaveresultedfromthepartialmeltingofthemantlewedgeinducedbythesubductionoftheoceaniccrustduringtheearlystagesoftectonicevolution.

ThezirconU-Pbdatingandwhole-rockgeochemicalanalysisprovideimportantinformationaboutthegeologicalevolutionandtectonicimplicationsoftheregion.Theageandgeochemicalcharacteristicsofthesyenogranitesuggestthatitwasgeneratedbypartialmeltingofmaficrocksormetasedimentaryrocksinapost-collisional,extensionalsetting.ThesefindingsprovideimportantinsightsintothetectonicevolutionoftheregionandcontributetotheunderstandingofthegeologicalprocessesthathaveshapedtheCentralAsianOrogenicBelt.TheLateJurassicalkalinesyenogranitefromtheJiaoxigouareaissignificantlyenrichedinincompatibletraceelements,LILEs,andLREEswithastrongnegativeEuanomaly.Thisgeochemicalsignatureindicatesthatthesyenogranitewasgeneratedbythemeltingofcrustalmaterialsthatwerepreviouslyenrichedintheseelements.

ThezirconU-Pbdatingrevealedthatthesyenogranitewasemplacedat151-152Ma,whichcorrespondstotheLateJurassicperiod.Thisgeologicalageisconsistentwiththepost-collisionalextensionalsettingthatoccurredduringthistime.

TheJiaoxigoualkalinesyenograniteisararetypeofrockanditsformationiscloselyrelatedtothetectonicevolutionoftheregion.TheoccurrenceofalkalinesyenograniteintheKorqinRightWingMiddleBannersuggeststhatthetectonicregimeduringtheLateJurassicwascharacterizedbyrifting,extension,andmantleupwelling.Thistectonicsettingisindicativeofapost-collisionalenvironment,whichisconsistentwiththeregionalgeologicalhistory.

TheJiaoxigoualkalinesyenograniteandneighboringvolcanicrocksrepresentanimportantrecordofLateJurassicpost-collisionalextensionalsettingintheCentralAsianOrogenicBelt.Theintrusiveandvolcanicrocksinthisregionhavenotbeenextensivelystudied,andfurtherresearchisneededtounderstandthetectonicevolutionoftheregionduringthistime.

Inconclusion,theLateJurassicalkalinesyenogranitefromtheJiaoxigouareaisanimportantgeologicalrecordofthetectonicevolutionoftheKorqinRightWingMiddleBannerandtheCentralAsianOrogenicBelt.Itsformationiscloselyrelatedtopost-collisionalextensionalsettingandmantleupwelling.ThegeochemicalandgeochronologicaldataprovideimportantinsightsintothegeologicalprocessesthathaveshapedthisregionandcontributetoabetterunderstandingofthetectonicevolutionoftheCentralAsianOrogenicBelt.FurtherresearchontheJiaoxigoualkalinesyenograniteandneighboringvolcanicrockscanprovidevaluableinformationonthemagmaticandtectonicprocessesduringtheLateJurassicperiod.Thecompositionofthesyenogranitesuggeststhatitwasformedbythepartialmeltingofcrustalrocksthatwereenrichedinincompatibletraceelements,LILEs,andLREEs.Therefore,furtherstudiesonthegeochemicalcompositionandmineralogyoftherockcanprovideinsightintothecrustalcompositionandinteractionbetweenthemantleandcrustduringtheLateJurassicperiod.

Moreover,theintrusiveandvolcanicrocksintheKorqinRightWingMiddleBannerhavepotentialasmineraldeposits.Preliminarystudieshaveindicatedthepresenceofgoldandothermineralsinthearea,andfutureexplorationcanprovideimportanteconomicbenefitstotheregion.Geophysicalsurveysandmappingcanalsoprovideimportantinformationonthestructuralgeologyoftheregion,whichcanaidinmineralexplorationandextraction.

TheJiaoxigoualkalinesyenograniteandneighboringvolcanicrockscanalsoprovideavaluablerecordofthepaleoclimateandpaleoenvironmentduringtheLateJurassicperiod.Thepresenceofvolcanicrocksintheregioncanindicateperiodsofvolcanicactivity,whichcanhaveasignificantimpactontheclimateandenvironment.Studyingthesedimentaryrocksintheregioncanalsoprovideinformationonthepaleoenvironmentandpotentialfossilrecords.

Inconclusion,theJiaoxigoualkalinesyenograniteandneighboringvolcanicrocksrepresentanimportantgeologicalandmineralogicalresourceintheKorqinRightWingMiddleBannerandtheCentralAsianOrogenicBelt.Furtherresearchcanprovidevaluableinformationonthemagmaticandtectonicprocesses,mineraldeposits,paleoclimate,andpaleoenvironmentduringtheLateJurassicperiod.Theregionhassignificantpotentialforeconomicandscientificdevelopment,andfurtherexplorationandresearchcanprovideimportantbe