Zircon U-Pb Geochronology and Hf Isotopic Constraints on Petrogenesis of Plagiogranite from the Cuomuqu Ophiolite,Bangong Lake Area,North Tibet  

作　　者：YIN Zhengxin YUAN Yajuan Lü Baofeng CAI Zhourong ZHENG Hao HUANG Qiangtai XIA Bin ZHONG Yun XIA Zhongyu SHI Xiaolong GUAN Yao 

机构地区：[1]School of Marine Sciences,Sun Yat-sen University [2]Key Laboratory of Offshore Oil Exploration and Development of Guangdong Higher Education Institutes [3]Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering

出　　处：《Acta Geologica Sinica(English Edition)》2015年第2期418-440,共23页地质学报（英文版）

基　　金：supported by the National Nature Science Foundation of China [No.41372208 and 41472054];the Foundation of China Geological Survey [No.1212011121259,1212011121262 and 1212011221087];the Open found of the State Key Laboratory of Ore Deposit Geochemistry,CAS [No.201304]

摘　　要：Field observation, geochemical signatures and zircon Hf isotope data indicate that Cuomuqu ophiolite in the Bangonghu area was formed in a back-arc basin （BAB） above a supra- subduction zone （SSZ）. Zircon U-Pb dating of the diabase from the Cuomuqu massif yielded an age of 164.3±1.9 Ma, thus indicating that the ophiolite complex was formed in the Middle Jurassic during back-arc extension of the mature Bangonghu-Nujiang Ocean. The zircon εHf（t） and TDMC values of the plagiogranite are similar to the εHf（t） and TDM of the diabase, respectively. The mode of occurrence of plagiogranites and their bulk-rock and Hf isotope characteristics indicate that they were derived from the mantle, associated with the surrounding gabbro and diabase, and were formed by partial melting of altered and hydrated mafic rocks under shear conditions during lateral drifting of the oceanic crust. The zircon U-Pb age of the plagiogranite is 156.4±1.4 Ma, and it is 7.9 Ma younger than the hosting diabase. In this study, zircon chronological and Hf isotopic data were tentatively analyzed to determine the genesis of plagiogranites in the Cuomuqu ophiolite complex.Field observation, geochemical signatures and zircon Hf isotope data indicate that Cuomuqu ophiolite in the Bangonghu area was formed in a back-arc basin （BAB） above a supra- subduction zone （SSZ）. Zircon U-Pb dating of the diabase from the Cuomuqu massif yielded an age of 164.3±1.9 Ma, thus indicating that the ophiolite complex was formed in the Middle Jurassic during back-arc extension of the mature Bangonghu-Nujiang Ocean. The zircon εHf（t） and TDMC values of the plagiogranite are similar to the εHf（t） and TDM of the diabase, respectively. The mode of occurrence of plagiogranites and their bulk-rock and Hf isotope characteristics indicate that they were derived from the mantle, associated with the surrounding gabbro and diabase, and were formed by partial melting of altered and hydrated mafic rocks under shear conditions during lateral drifting of the oceanic crust. The zircon U-Pb age of the plagiogranite is 156.4±1.4 Ma, and it is 7.9 Ma younger than the hosting diabase. In this study, zircon chronological and Hf isotopic data were tentatively analyzed to determine the genesis of plagiogranites in the Cuomuqu ophiolite complex.

关 键 词：Bangonghu-Nujiang suture zone OPHIOLITE PLAGIOGRANITE zircon U-Pb dating zircon Hf isotope tectonic setting 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]