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Petrogenesis of Late Cretaceous Jiangla'angzong I-Type Granite in Central Lhasa Terrane, Tibet, China: Constraints from Whole-Rock Geochemistry, Zircon U-Pb Geochronology, and Sr-Nd-Pb-Hf Isotopes

查看全文 作　　者：LIU [1]Hong;LI [1]Guangming;HUANG [1]Hanxiao;CAO [1]Huawen;YUAN [2]Qian;LI [1]Yingxu;OUYANG [1]Yuan;LAN [3]Shuangshuang;LU [3]Menghong;YAN [4]Guoqiang 高影响力作者 机构地区：[1]Chengdu Center, China Geological Survey, Chengdu 610081, China;[2]Faculty of Earth Resources, China University of Geosciences, Wuhan 430074, China;[3]Sichuan Institute of Metallurgical Geology & Exploration, Chengdu 610051, China;[4]Tianjin Center, China Geological Survey, Tianjin 300170, China高影响力机构 出　　处：《Acta Geologica Sinica(English Edition)》索引2018年第92卷第4期,共19页高影响力期刊 基　　金：financially supported by the National Key Research and Development Program of China (Grant No.2016YFC0600308, SQ2018YFC060162);the China Geological Survey Project (Grant No.DD20160015,DD20160026);the International Scientific Plan of the Qinghai Xizang (Tibet) Plateau of Chengdu Center, China Geological Survey;the Natural Science Foundation of China (Grant No.41702080, 41702086) 摘　　要：The Jiangla'angzong granite in the northern part of the Central Lhasa Terrane is composed of syenogranite and adamellite. LA-ICP-MS zircon U-Pb analyses suggest that syenogranite has a weighted mean ^(206) Pb/^(238) U age of 86±1 Ma(mean square weighted deviation=0.37), which is in accordance with the muscovite Ar-Ar age(85±1 Ma) of Cu-Au ore-bearing skarns and the zircon U-Pb age(84±1 Ma) of adamellite. This suggests that the Jiangla'angzong magmatism and Cu–Au mineralization events took place during the Late Cretaceous. The granite contains hornblende, biotite, and pyroxene, and does not contain Al-bearing minerals, such as muscovite, cordierite, and garnet. It has high contents of SiO_2(65.10–70.91 wt%), K_2O(3.44–5.17 wt%), and total K_2O+Na_2O(7.13–8.15 wt%), and moderate contents of A_(12)O_3(14.14–16.45 wt%) and CaO(2.33–4.11 wt%), with a Reitman index(σ43) of 2.18 to 2.33, and A/CNK values of 0.88 to 1.02. The P_2O_5 contents show a negative correlation with SiO_2, whereas Pb contents show a positive correlation with SiO_2. Th and Y contents are relatively low and show a negative correlation with the Rb contents. These characteristics suggest that the Jiangla'angzong granite is a high K calc–alkaline metaluminous I–type granite. It is enriched in light rare earth elements(LREE) and large ion lithofile elements(LILE), and depleted in heavy rare earth elements(HREE) and high field strength elements(HFSE), with LREE/HREE ratios of 11.7 to 18.1. The granite has negative Eu anomalies of 0.58 to 0.94 without obvious Ce anomalies(δCe=1.00–1.04). The relatively low initial 87 Sr/86 Sr ratios of 0.7106 to 0.7179, positive εHf(t) values of 1.0 to 4.1, and two-stage Hf model ages(TDM2) ranging from 889 Ma to 1082 Ma, These geochemical features indicate that the granite derived from a juvenile crust. The(^(143) Nd/^(144) Nd)_t values from the Jiangla'angzong granite range from 0.5121 to 0.5123, its εNd(t) values range from-10.17 to-6.10, its(^(206) Pb/^(204) Pb)_t values range from 18.683 to 18.746, its(^(207) Pb/^(204) Pb)_t values range from 15.695 to 15.700, and its(^(208) Pb/^(204) Pb)_t values range from 39.012 to 39.071. These data indicate that the granite was formed by melting of the upper crust with the addition of some mantle materials. We propose that the Jiangla'angzong granite was formed during the postcollision extension of the Qiangtang and Lhasa terranes. 关 键 词：U-PB 花岗石 白垩纪 地球年代学 岩层 拉萨 地球化学 锆石
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