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《Geological Bulletin of China》 2014-07
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LA-ICP-MS zircon U-Pb age and geochemical characteristics of the acid intrusive rocks in the western part of Bangong Lake-Nujiang River suture zone

ZHANG Xiang-fei;LI You-guo;CAO Xiao-min;QU Xiao-ming;XIN Hong-bo;WANG Jian;DU De-dao;Institute of Mineral Resources, Yunnan Geological Survey;School of Earth Science, Chengdu University of Technology;Institute of Mineral Resources, CAGS;Beijing Research Institute of Uranium Geology;Research Institute of Petroleum Exploration & Development, Petro-China;  
To investigate the closure time of the Bangong-Nujiang Middle Tethys Ocean, the authors chose small acid rock masses in the ophiolitic zone near the Bangong Lake in Rutog County of Tibet as the study object to investigate their petrogenesis and structural environment. The rock type is plagioclase granite-porphyry. Chemically the rocks consist mainly of SiO2and(K2O+Na2O),with their content being 65.78%~68.76% and 6.39%~6.86% respectively. In addition, the rocks have high LREE enrichment, high degree of fractionation and positive Eu anomalies They are rich in LREE such as Sr, Ba and Rb, but are depleted in high field strength elements(HFSE) like Ta, Ti and Nb, assuming a "valley" form. The depletion of Nb and Ta suggests that they have the typical characteristics of arc magmatite. LA-ICP-MS(inductively coupled plasma-mass spectrometer and a laser ablation system) dating shows that the zircon206Pb/238U weighted mean ages of two plagioclase granite-porphyry samples are 96.08Ma±0.22 Ma and 96.05Ma±0.30 Ma respectively, implying that they both belong to the Late Cretaceous period of Mesozoic.
【Fund】: 中国地质调查局项目(编号:1212010818097)
【CateGory Index】: P597.3;P588.12
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