简介：Thereisageneralconsensusthatmostophiolitesformedabovesubductionzones(Pearce,2003),particularlyduringforearcextensionatsubductioninitiation(Shervais,2001;Stern,2004;WhattamandStern,2011).'Supra-Subductionzone'(SSZ)ophiolitessuchasthewell-studiedTethyanophiolites,generallydisplayacharacteristicsequentialevolutionfrommid-oceanicridgebasalts(MORBs)toislandarctholeiities(IATs)orbonites(BONs)(Pearce,2003;DilekandFurnes,2009,2011),whichweregeneratedinsequencefromthedecompressionmeltingofasthenosphericmantleandpartialmeltingofsubduction-metasomatizeddepletedmantle(SternandBloomer,1992;DilekandFurnes,2009;WhattamandStern,2011).However,ophioliteswithMORBand/oroceanic-islandbasalt(OIB)affinitiesarerare,andtheiroriginandtectonicnaturearepoorlyunderstood(Boedoetal.,2013;Saccanietal.,2013).ItisinterestingthatthecompositionoftheseophiolitesfromthecentralTibetanPlateau(CTP)isdominatedbyMORBsandminorOIBsandadistinctlackofIATsandBONs,whichisinconsistentwithmostophiolitesworldwide(RobinsonandZhou,2008;Zhangetal.,2008).Butthegenerationandtectonicnatureoftheseophiolitesarestillcontroversial.*Inthisstudy,wepresentnewgeochronological,mineralogicalandSr-NdisotopicdatafortheChayongandXiewumaficcomplexesinthewesternGarzê-Litangsuturezone(GLS),atypicalPaleo-TethyansuturecrossingtheCTP(Fig.1).TheTriassicophioliteinthewesternGLShasbeendescribedbyLietal.(2009),whofoundthatitmainlyconsistsofgabbros,diabases,pillowbasaltsandafewmetamorphicperidotites.TheophiolitehasbeentectonicallydismemberedandcropsoutinTriassicclasticrocksandlimestonesastectonicblocks.TheChayongandXiewumaficcomplexesaregenerallyregardedasimportantfragmentsoftheTriassicophiolites(e.g.,Jin,2006;Lietal.,2009).ZirconLA-ICP-MSU-Pbagesof234±3Maand236±2MacanbeinterpretedasformationtimesoftheChayongandXiewumaficcomplexes,respectively.Thebasalts