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  

作　　者：XIE Zhipeng WU Xuelu WANG Tengfei XUE Chuandong YANG Tiannan WANG Wei SUI Binxi XIN Di 

机构地区：[1]Department of Earth Sciences,Kunming University of Science and Technology,Kunming 650093,China [2]Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China

出　　处：《Acta Geologica Sinica(English Edition)》2022年第3期858-874,共17页地质学报（英文版）

基　　金：This study was financially supported by the Major Science and Technology Special Plan of Yunnan Province(Grant No.202202AG050006);the National Natural Science Foundation of China(Grant No.41603032);the Applied Basic Research Foundation of Yunnan Province(Grant No.2017FB075);the Yunnan Key Research and Development Program(Grant No.2015CB452601),and the China Geological Survey(Grant No.12120114064301).

摘　　要：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 withεNd(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.Com

关 键 词：geochemistry PETROGENESIS WEHRLITE OIB Changning-Menglian Belt PALEO-TETHYS Tournaisian Manxin Tibetan plateau 

分 类 号：P542[天文地球—构造地质学]