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《Acta Geologica Sinica》 2018-06
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The Determination of the Early Jurassic Magmatism in the Middle Gangdese Batholith,Southern Tibet and its Tectonic Significance

MENG Yuanku;XU Zhiqin;XU Yang;LI Rihui;SUN Jingbo;ZHANG Kuihua;College of Earth Science and Engineering,Shandong University of Science and Technology;Institute of Geology,Chinese Academy of Geological Sciences;School of Earth Sciences and Engineering,Nanjing University;Exploration and Development Research Institute,Sinopec Shengli Oilfield;  
In this paper,we conducted systematically zircon LA-ICP-MS U-Pb dating,Lu-Hf isotopic analyses and whole-rock geochemical analyses for two granitic plutons(Donggagranitic pluton and Numa granitic pluton),and elucidated their petrogenesis and tectonic setting in the middle Gangdese batholith,southern Tibet.The Donggagranitic pluton is mainly composed of quartz and feldspar,with minor amount of biotite and hornblende.The Numa granitic pluton consists of quartz and feldspar dominantly as well as minor amount of biotite.The zircon U-Pb dating yielded a mean age of 185.8±2.3 Ma for the Dongga pluton and two mean ages of 185.9±2.2 Ma and 185.1±1.7 Ma for the Numa pluton.The results show the similar diagenesis ages,indicating they were the products of the simultaneous magmatic event in the Gangdese batholith,southern Tibet.Geochemically,two granitic plutons show enrichment of LREE and LILE as well as depletions of HFSE(Nb,Ta and Ti),suggesting a subduction-related tectonic setting.Rittmann and Aluminium saturation signatures suggest that those two granitic plutons belong to typical calc-alkaline and weak peraluminous(A/CNK)I-type granite.Zircon Hf isotopic components demonstrate that the Dognga and Numa plutons are characterized by highly depleted Hf isotopic compositions and young second model ages(t_(DM2)),with theεHf(t)values of+11.14~+15.55(mean value+13.76)and+9.49~+15.52(mean value +13.56),respectively,indicating that the granitic plutons originated from partial melting of juvenile crustal materials.During the partial melting,underplating mantle magma played a key role in causing the partial melting of the lower crustal juvenile materials in the Gangdese belt.Integrated study,along with previous studied results,indicates that the granitic plutons were generated in an active continental margin arc setting related to the northward subduction of the Neo-Tethys oceanic crust beneath the Lhasa terrane during the Early Jurassic(Pliensbachian stage)in the Gangdese belt,southern Tibet.
【Fund】: 中国博士后基金面上基金(编号M2017612220);; 山东省自然科学基金博士基金(编号ZR2017BD033);; 中国地质调查局工作项目(编号DD20160139)联合资助
【CateGory Index】: P534.52;P588.1
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