The Changning-Menglian Belt represents the main Paleo-Tethyan Suture in the southeastern Tibetan Plateau,which divides Gondwana-and Eurasia-derived continental fragments from each other.The belt contains ultramafic-mafic volcanic rocks that provide evidence of the tectonic processes which operated during the evolution of the Paleo-Tethyan Ocean.New geochemical data for Early Carboniferous volcanics in the southern Changning-Menglian Belt show that wehrlites have cumulate and poikilitic textures,and contain low-Fo(84.2-87.2)olivine,clinopyroxene with low Mg#values(79.4-85.6),and spinel with high Cr#values(67.8-72.4).Estimated equilibrium temperatures obtained using olivine-spinel Fe-Mg exchange geothermometry range from 978℃to 1373℃(mean=1205℃;n=3).These observations combined with a lack of reaction or melt impregnation textures indicate that these units represent magmatic cumulates rather than having formed as a result of mantle-melt reactions.Both wehrlites and basalts in the belt have subparallel rare earth element(REE)-and primitive-mantle-normalized multi-element patterns with slightly positive Nb-Ta anomalies,but negligible Eu and Zr-Hf anomalies.The volcanics have similar Sr-Nd-Pb isotopic compositions with εNd(t)values of 4.2-4.5(mean=4.3;n=3)and 4.0-4.4(mean 4.2;n=4),respectively,and also have similar immobile element ratios,such as Nb/La,Nb/U,Th/La,Zr/Nb,Th/Ta,La/Yb,Nb/Th,Nb/Y,and Zr/Y.These characteristics indicate both units have ocean island basalt(OIB)-like geochemical affinities,consistent with the fact that the clinopyroxene in the wehrlites is compositionally similar to OIB-related cumulus clinopyroxene.This suggests that both the wehrlites and basalts were derived from similar parental magmas that underwent generally closed-system magmatic differentiation dominated by fractionation of the olivine and clinopyroxene.This parental magma was likely generated in an oceanic seamount setting from an OIB-type mantle source(i.e.,asthenospheric mantle)containing garnet-spinel lherzolite material.Combing this new data with that from oceanic seamount volcano-sedimentary suites derived from previous research enables the identification of a mature late Paleozoic ocean basin between the passive northeastern Gondwanan margin and the northward-migrating microcontinent of Lanping-Simao.

Department of Earth Sciences,Kunming University of Science and Technology,Kunming 650093,China;Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China

[1]XIE Zhipeng;WU Xuelu;WANG Tengfei;XUE Chuandong;YANG Tiannan;WANG Wei;SUI Binxi;XIN Di-.Petrogenesis of Early Carboniferous Ultramafic-Mafic Volcanic Rocks in the Southern Changning-Menglian Belt,Southeastern Tibetan Plateau:Implications for the Evolution of the Paleo-Tethyan Ocean)[J].地质学报（英文版）,2022(03):858-874

Ultramafic,Mafic,Changning,Menglian,volcanics,wehrlites,poikilitic,Mg#values,Cr#values,geothermometry,cumulates,subparallel,microcontinent,Lanping,Simao

Petrogenesis,Early,Carboniferous,Volcanic,Rocks,Southern,Belt,Southeastern,Tibetan,Plateau,Implications,Evolution,Tethyan,Ocean,represents,main,Suture,southeastern,which,divides,Eurasia,derived,continental,fragments,from,each,belt,contains,ultramafic,rocks,that,provide,evidence,tectonic,processes,operated,during,evolution,New,geochemical,data,southern,show,have,textures,low,Fo,olivine,clinopyroxene,spinel,high,Estimated,equilibrium,temperatures,obtained,using,exchange,range,mean,These,observations,combined,lack,melt,impregnation,indicate,these,units,magmatic,rather,than,having,formed,result,mantle,reactions,Both,basalts,rare,earth,element,REE,primitive,normalized,multi,patterns,slightly,positive,Nb,Ta,anomalies,but,negligible,Zr,Hf,similar,Sr,Nd,Pb,isotopic,compositions,respectively,also,immobile,ratios,such,Yb,characteristics,both,island,OIB,affinities,consistent,fact,compositionally,related,cumulus,This,suggests,were,parental,magmas,underwent,generally,closed,system,differentiation,dominated,by,fractionation,was,likely,generated,oceanic,seamount,setting,type,source,asthenospheric,containing,garnet,lherzolite,material,Combing,this,new,volcano,sedimentary,suites,previous,research,enables,identification,mature,Paleozoic,basin,between,passive,northeastern,Gondwanan,margin,northward,migrating

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