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Geochemistry,Hf-Sr-Nd Isotopes and Petrogenesis of Acidic Volcanic Rocks in Quzhuomu Region of Southern Tibet

Dong Suiliang;Zhang Zhi;Zhang Linkui;Li Guangming;Qing Chengshi;Liang Wei;Fu Jiangang;Cao Huawen;Li Haiping;Xu Changhui;Li Zhipeng;Chengdu Center of China Geological Survey;Sichuan Bureau of Geology and Mineral Resources of109 Geological Team;  
There are few related studies on the Cretaceous acid rocks currently,and this paper focuses on a wide range of acid(dyanite)-basic(diabase-basalt)volcanic magmatism recently discovered in the Quzhuomu area where bimodal volcanic magmatic activity is obvious.Geochronology,geochemistry and Hf-Sr-Nd isotope analyses are carried out on these dacites.The results show that the diagenetic age of dacite is 142.0±2.5 Ma.The dacites show high contents of LREE and high field-strength elements(etc.Nb,Zr,Hf,Y)and high ratios of Ga/Al,indicating the characteristics of A-type granite.εHf(t)values of zircons range from-13.1 to-2.4,with an average of-7.1.The dacites also show high initial Sr isotope contents(~(87)Sr/~(86)Sr ratios of 0.722 024 to 0.722 698)and low initial Nd isotope contents with εNd(t)values from-12.2 to-11.8).The comprehensive research indicates that the acid volcanic rocks of Quzhuomu region are the products of the continental crust anataxis under ex-tension setting.These dacites show the similar geochemical characteristics and diagenetic age with the Sangxiu formation acid volcanic rocks,Laguila acid intrusive rocks and rhyolites of Sangrize region.They are probably all the products of the ComeiBunbury large igneous province,which are the products of the early magmatic activity of Kerguelen mantle plume.The magma activities of Kerguelen mantle plume may be advanced to 140 Ma.
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