內(nèi)蒙中部蘇左旗早石炭世火山巖年代學(xué)與地球化學(xué)研究

內(nèi)蒙中部蘇左旗早石炭世火山巖年代學(xué)與地球化學(xué)研究摘要

內(nèi)蒙古中部蘇左旗位于東亞大陸東緣，是一個火山巖較為廣泛分布的地區(qū)，研究該區(qū)域火山巖年代與地球化學(xué)特征具有重要的學(xué)術(shù)價值。本文選取該地區(qū)早石炭世火山巖為研究對象，通過野外地質(zhì)調(diào)查、巖石薄片觀察、地球化學(xué)分析等多種方法，對該區(qū)域火山巖的年代學(xué)及地球化學(xué)特征進(jìn)行了深入研究。

研究結(jié)果表明，該區(qū)域火山巖主要分布在蘇左旗北部和東北部，呈現(xiàn)出花崗安山巖和玄武巖交替出現(xiàn)的地質(zhì)特征。通過對K-Ar等年代學(xué)分析，確定該區(qū)域火山巖的形成時間為早石炭世，形成時代距今約為3.9億年。地球化學(xué)特征表明，蘇左旗火山巖中富集了Rb、Sr、Ba等大離子親石元素，以及Nb、Th、La等高場強(qiáng)元素，同時富集了輕稀土元素，輕重稀土元素配分較平坦，證明該區(qū)域火山巖源區(qū)物質(zhì)來自地幔，并受到了殼源物質(zhì)的摻雜。

關(guān)鍵詞：內(nèi)蒙古；蘇左旗；早石炭世；火山巖；年代學(xué)；地球化學(xué)特征

Abstract

SuLeftBanner,locatedattheeasternmarginoftheEastAsiacontinent,isanareawithawidedistributionofvolcanicrocks,whichhasimportantacademicvaluetostudytheageandgeochemicalcharacteristicsofvolcanicrocksinthisarea.Inthispaper,theearlyCarboniferousvolcanicrocksinthisareawereselectedastheresearchobject,andacomprehensivestudyofthegeochronologyandgeochemicalcharacteristicsofvolcanicrocksintheregionwascarriedoutbyfieldgeologicalinvestigation,rockthinsectionobservation,andgeochemicalanalysis.

TheresultsshowthatthevolcanicrocksinthisareaaremainlydistributedinthenorthandnortheastofSuLeftBanner,presentinggeologiccharacteristicsofalternationofgraniteanddiabase.TheformationtimeofthevolcanicrocksinSuLeftBannerwasdeterminedasearlyCarboniferousbyK-Argeochronologicalanalysis,withanageofabout390millionyearsago.GeochemicalcharacteristicsshowedthatthevolcanicrocksinSuLeftBannerarerichinlargeionlithophileelementssuchasRb,Sr,Ba,andhighfieldstrengthelementssuchasNb,Th,andLa,andarealsoenrichedinlightrareearthelements,withaflatdistributionofLREEandHREE,indicatingthatthesourcematerialofthevolcanicrocksinthisareacamefromthemantleandwasmixedwithcrustalsourcematerial.

Keywords:InnerMongolia;SuLeftBanner;EarlyCarboniferous;Volcanicrocks;Geochronology;GeochemicalcharacteristicTheSuLeftBannerofInnerMongoliaislocatedinthenorthernpartofChinaandisknownforitsvolcanicrocksthatwereformedduringtheEarlyCarboniferousperiod.Thegeochronologyoftheserockshasbeenstudied,andithasbeenfoundthattheywereformedapproximately340millionyearsago.

ThevolcanicrocksinSuLeftBannerarecharacterizedbytheirrichcontentoflargeionlithophileelementssuchasRb,Sr,BaandhighfieldstrengthelementssuchasNb,Th,andLa.Inaddition,theyarealsoenrichedinlightrareearthelements,withaflatdistributionofLREEandHREE.

Theenrichmentoftheseelementsisanindicationthatthesourcematerialofthevolcanicrocksinthisareacamefromthemantleandwasmixedwithcrustalsourcematerial.TheflatdistributionofLREEandHREEalsosuggeststhattherewasnotasignificantfractionationprocesstakingplaceduringtheformationoftheserocks.

Overall,thevolcanicrocksinSuLeftBannerprovidevaluableinsightsintothegeologicalhistoryoftheregionandtheprocessesthathaveshapeditovermillionsofyears.ThegeochronologyandgeochemicalcharacteristicsoftheserocksofferimportantcluesabouttheoriginsandevolutionoftheEarth'scrustinthisareaFurthermore,thevolcanicrocksinSuLeftBannerarecrucialtounderstandingtheroleoftectonicprocessesintheformationoftheregion.ThegeochronologydatasuggeststhattherockswereformedduringtheMesozoicEra,whichwasmarkedbysignificantplatetectonicactivity.

Duringthistime,theregionexperiencedavarietyoftectonicevents,includingtheformationoftheMongolianPlateau,theclosureoftheMongol-OkhotskOcean,andthecollisionbetweentheSiberianandNorthChinaBlocks.Thesetectoniceventsledtotheformationofvariousgeologicalstructures,includingtheYinshanandDaHingganMountains.

Thegeochemicaldataofthevolcanicrocksalsoprovidesinsightintothesourceofthemagmathatformedtherocks.Therocksaremainlycomposedofandesiticandrhyoliticcompositions,whicharetypicallyassociatedwithsubductionzones.Thissuggeststhatthemagmawaslikelyderivedfromthesubductionofoceaniccrustbeneaththecontinentalcrust.

Moreover,thehighaluminumcontentoftherocksindicatesthattheywerelikelyderivedfromafelsicsource.Thisisconsistentwiththesubductionofoceaniccrust,whichtypicallyresultsinthemeltingoftheoverlyingcontinentalcrusttoformfelsicmagma.

Overall,thevolcanicrocksinSuLeftBannerofferimportantinsightsintothetectonicprocessesandgeologicalhistoryoftheregion.TheyprovidecrucialinformationabouttheformationandevolutionoftheEarth'scrustinthisareaandtheroleofplatetectonicsinshapingtheregionovermillionsofyearsInadditiontothevolcanicrocksinSuLeftBanner,therearealsoothertypesofrocksintheregionthatprovideimportantinformationaboutthegeologicalhistoryofthearea.OneexampleisthesedimentaryrocksfoundinthenearbyXiamalingFormation,whichdatesbacktotheNeoproterozoicEra(1,000to541millionyearsago).Theserocksarebelievedtohaveformedinashallowmarineenvironment,possiblyasaresultofthebreakupofthesupercontinentRodinia.

AnotherimportantaspectofthegeologyoftheSuLeftBannerregionisthepresenceoffaultsandfolds.Thesestructuresareindicativeofthedeformationthathasoccurredintheregionovermillionsofyears,asaresultoftectonicmovementandplatecollisions.Thegeologyoftheareaalsosuggeststhattheremayhavebeenmultipleperiodsofupliftanderosion,whichhaveresultedintheexposureofdifferentrocktypesandtheformationofdistinctgeologicalfeatures.

Overall,thestudyofthegeologyofSuLeftBannerandthewiderregionprovidesvaluableinsightsintotheprocessesthathaveshapedtheEarthovermillionsofyears.Byunderstandingthegeologicalhistoryofanarea,scient