A greenstone belt in southeast Tibet:An accreted middle–late Permian oceanic plateau  

作　　者：Bin Wang Chao-Ming Xie Chris Yakymchuk Yong-sheng Dong Yu-hang Song Meng-long Duan 

机构地区：[1]College of Earth Sciences,Jilin University,Changchun 130061,China [2]Key Laboratory of Mineral Resources Evaluation in Northeast Asia,Ministry of Natural Resources of China,Changchun 130061,China [3]Research Center for Tibetan Plateau,Jilin University,Changchun 130061,China [4]Department of Earth and Environmental Sciences,University of Waterloo,Waterloo,Ontario N2L 3G1,Canada

出　　处：《Geoscience Frontiers》2023年第3期117-130,共14页地学前缘（英文版）

基　　金：funded by the National Natural Science Foundation of China(Grant number 42172226);the Indepen-dent research fund of Key Laboratory of Mineral Resources Evaluation in Northeast Asia,Department of Natural Resources(DBYZZ-18-06).

摘　　要：Studies of accreted oceanic plateau sections provide crucial information on their structures,compositions,and origins.We investigate the petrogenesis of ultramafic–mafic rocks in the Tangjia–Sumdo greenstone belt of southeast Tibet using petrography,whole-rock geochemistry,and U-Pb zircon geochronology.These rocks are divided into four groups based on geochemical characteristics that include depleted and tholeiitic mafic rocks,transitional mafic rocks,enriched and alkaline mafic rocks,and picritic ultramafic rocks.Depleted and tholeiitic mafic rocks have the oldest crystallization ages(-272 Ma),followed by picritic ultramafic rocks(-270 Ma),transitional mafic rocks(267–254 Ma),and enriched and alkaline mafic rocks(252–250 Ma).Hafnium and neodymium isotope ratios of depleted and tholeiitic mafic rocks(ε_(Hf)(t)=+13.1–+16.9;ε_(Nd)(t)=+6.9–+7.1),transitional mafic rocks(ε_(Hf)(t)=+1.8–+16.9;ε_(Nd)(t)=+0.8–+5.5),enriched and alkaline mafic rocks(ε_(Hf)(t)=+0.5–+5.4;ε_(Nd)(t)=1.5 to+1.9)and picritic ultramafic rocks(ε_(Hf)(t)=+14.9–+17.2;ε_(Nd)(t)=+7.8–+9.0)are similar to those of N-MORB,E-MORB,OIB and depleted-type picritic mafic rocks in other oceanic plateaus,respectively.The geochemical characteristics of the depleted and tholeiitic mafic rocks suggest that they formed by partial melting of depleted spinel lherzolite in a mid-ocean ridge setting,whereas the picritic ultramafic rocks suggest a high degree of partial melting of depleted lherzolite in a hot mantle plume head.The transitional mafic rocks formed by partial melting of moderately enriched garnet lherzolite.The youngest rocks(enriched and alkaline mafic rocks)formed by partial melting of a more enriched garnet lherzolite(compared to transitional mafic rocks)at relatively low temperatures.We propose that the depleted and tholeiitic mafic rocks represent normal oceanic crust of the Sumdo Paleo-Tethys Ocean and the transitional mafic rocks,enriched and alkaline mafic rocks and picritic ultramafic rocks are the fragments of the o

关 键 词：Oceanic plateau Mantle plume PALEO-TETHYS TIBET Greenstone belts 

分 类 号：P534.45[天文地球—古生物学与地层学] P542[天文地球—地质学]