Thermal Structure and Rheology of the Upper Mantle Derived from Mantle Xenoliths from Gansu Province, Western China-中国期刊网

摘要 MantlexenolithsbroughtupbyCenozoicvolcanicrocksontotheearth'ssurfacemayprovidedirectinformationabouttheuppermantlebeneaththevolcanicregion.ThispaperpresentsthestudyonmantlexenolithscollectedfromHaotivillage,DangchangCounty,GansuProvince,westernChina.Themainpurposeofthestudyistogainaninsightintothethermalstructureandrheologyoftheuppermantlebeneaththeregion.Theresultsshowthattheuppermantleoftheregioniscomposedmainlyofspinellherzoliteatshallowerdepth(52～75km),andgarnetlherzoliteatgreaterdepth(greaterthan75km),insteadofharzburgiteandduniteasproposedbysomepreviousstudies.TheuppermantlegeothermderivedfromtheequilibriumtemperaturesandpressuresofxenolithsfromtheregionislowerthanthatofNorthChina,andissomewhatclosertotheOceanicgeotherm.Thecrust-mantleboundaryisdeterminedfromthegeothermtobeatabout52km,andtheMohoseemstobethetransitionzoneoflowercrustmaterialwithspinellherzolite.Ifwetake1280℃asthetemperatureofthetopofasthenosphere,thenthelithosphere-asthenosphereboundaryshouldbeatabout120kmdepth.Thedifferentialstressoftheuppermantleisdeterminedbyusingrecrystallizedgrainsizepiezometry,whilethestrainrateandequivalentviscosityaredeterminedbyusingthehightemperatureflowlawofperidotite.Thedifferentialstress,strainrateandviscosityprotidesconstructedonthebasisoftheobtainedvaluesindicatethatasthenosphericdiapiroccurredinthisregionduringtheCenozoictime,resultinginthecorrespondingthinningofthelithosphere.However,thescaleandintensityofthediapirwassignificantlylessthanthatoccurringintheNorthChinaregion.Moreover,numeroussmall-scaleshearzoneswithlocalizeddeformationmightoccurinthelithosphericmantle,asevidencedbytheextensiveoccurrenceofxenolithswithtabularequigranulartexture.

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Thermal Structure and Rheology of the Upper Mantle Derived from Mantle Xenoliths from Gansu Province, Western China

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Thermal Structure and Rheology of the Upper Mantle Derived from Mantle Xenoliths from Gansu Province, Western China

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