Identification of the Early Jurassic mylonitic granitic pluton and tectonic implications in Namling area,southern Tibet  

作　　者：Yuanku Meng Walter D.Mooney Runlong Fan Jinqing Liu Youqing Wei 

机构地区：[1]College of Earth Science and Engineering,Shandong University of Science and Technology,Qingdao 266590,China [2]U.S.Geological Survey,Menlo Park,CA 94025,USA [3]SHRIMP Center,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 102206,China

出　　处：《Geoscience Frontiers》2021年第1期13-28,共16页地学前缘（英文版）

基　　金：co-supported by the Natural Science Foundation of Shandong Province(Grant No.ZR2019QD002);the National Natural Science Foundation of China(Grant No.41902230);the Key Laboratory of DeepEarth Dynamics of Ministry of Natural Resources(Grant No.J1901-16);the Young innovative projects of Shandong Province(Grant No.2019KJH004);the research foundation of China Geological Survey(JYYWF20181702)。

摘　　要：A number of studies revealed that the Gangdese magmatic belt of southern Tibet was closely related to the northward subduction of the Neo-Tethys oceanic lithosphere and Indo-Asian collision.However,pre-Cretaceous magmatism is still poorly constrained in the Gangdese magmatic belt,southern Tibet.Here,we conducted systematically geochronology and geochemistry studies on a newly-identified granitic pluton in the middle Gangdese magmatic belt(Namling area),southern Tibet.Zircon SHRIMPⅡU-Pb dating for one representative sample gives a weighted age of 184.2±1.8 Ma(MSWD=±1.11),corresponding to emplacement and crystallization age of the granitic pluton in the Early Jurassic(Pliensbachian).High SiO2(68.9-72.1 wt.%)contents and intermediate Mg#values(35-38)together suggest that the newly-identified granitic pluton was probably formed by partial melting of crustal material with minor injection of mantle-derived magma,precluding an origin from melting of metasedimentary rocks that are characterized by low Mg#and high zirconδ^18O values(>8‰).Geochemically,the newly-identified granitic pluton belongs to typical I-type granitic affinity,whereas this is inconsistent with aluminium saturation index(ASI=A/CNK ratios)and geochemical signatures.This suggests that zircon oxygen isotopes(4.30‰-5.28‰)and mineral features(lacking Al-rich minerals)are reliable indicators for discriminating granitic origin.Significantly depleted whole-rock Sr-Nd-Hf isotopic compositions and zirconεHf(t)values indicate that the granitic pluton was derived from partial melting of depleted arc-type lavas.In addition,the granitic pluton shows zirconδ^18O values ranging from 4.30‰to 5.28‰(with a mean value of 4.77‰)that are consistent with mantle-derived zircon values(5.3‰±0.6‰)within the uncertainties,indicating that the granitic pluton might have experienced weak short-living high-temperature hydrous fluid-rock interaction.Combined with the Sr-Nd-Hf-O isotopes and geochemical signatures,we propose that the newly-identified granitic pl

关 键 词：Sr-Nd-Hf-O isotopes SHRIMP U-Pb dating Early Jurassic Mylonitic granitic pluton Gangdese belt 

分 类 号：P588.121[天文地球—岩石学] P534.52[天文地球—地质学]