期刊
GONDWANA RESEARCH
卷 41, 期 -, 页码 65-76出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.gr.2015.09.004
关键词
Tibetan plateau; Zhongba terrane; Adakitic rocks; Petrogenesis; Lower crust
资金
- National Natural Science Foundation of China [41572188, 41172129]
- China Geological Survey [1212011086037, 1212011221103]
- National Key Project for Basic Research of China [2011CB822001]
Post-collisional adakitic rocks (26-9 Ma) have been recognized in southern Tibet for almost 20 years; however, their origins and geodynamics remain highly controversial. This paper reports geochronological and geochemical data for the Lasa intrusion exposed in the Zhongba terrane and proposes implications for the origins of the Miocene adakitic rocks in southern Tibet. The Lasa intrusion consists of granite and granodiorite porphyries with zircon U-Pb ages of ca. 16 Ma. The porphyries have high SiO2 (65.14-67.61 wt.%), Al2O3 (15.13-16.10 wt.%), K2O (2.87-3.54 wt.%), and Sr (727-1046 ppm) contents and low Y (9-13 ppm) and Yb (0.82-1.19 ppm) contents. They are enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs). The porphyries display relatively low MgO contents (1.39-1.98 wt.%), high Sr/Y (65-98) and (La/Yb)(N) (18.8-25.5) ratios, initial (Sr-87/Sr-86)(i) ratios of 0.70912-0.70805, epsilon(Nd)(t) values of -6.4 to -7.9, (Pb-206/Pb-204)(t) ratios of 18.7108-18.7665, (Pb-207/Pb-204)(t) ratios of 15.6837-15.7118, and (Pb-208/Pb-204)(t) ratios of 39.1600-39.3034. These signatures indicate that the Lasa porphyries are adakitic rocks derived from the partial melting of a thickened lower crust. The Miocene adakitic rocks in the Zhongba terrane have similar Sr-Nd isotopic compositions to those of western Lhasa and the Himalaya terrane, which differ from coetaneous adakitic rocks of the eastern Lhasa terrane in terms of Sr-Nd isotopic compositions. Based on the spatial distributions and isotopic features of the post-collisional adakitic rocks in southern Tibet, we suggest that all of the adakitic rocks were derived from the partial melting of thickened lower crust and that their geochemical variations are mainly caused by the heterogeneity of lower crust. (C) 2015 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据