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Geochronology and geochemistry of Mesoproterozoic granitoids in the Lhasa terrane, south Tibet: implications for the early evolution of the Lhasa terrane

Xu, Wang-Chun; Zhang, Hong-Fei; Harris, Nigel; Guo, Liang; Pan, Fa-Bin and Wang, Shuai (2013). Geochronology and geochemistry of Mesoproterozoic granitoids in the Lhasa terrane, south Tibet: implications for the early evolution of the Lhasa terrane. Precambrian Research, 236 pp. 46–58.

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The early history of the Lhasa terrane remains poorly constrained due to the poor exposure of the Proterozoic rocks. We report here U–Pb zircon ages, geochemical and Hf isotopic data for granite gneisses and biotite gneisses from the Bomi Complex in the eastern part of the Lhasa terrane, south Tibet. Petrological and geochemical data suggest that the protoliths of the granite gneisses and the biotite gneisses could be granites and tonalites, respectively. LA-ICPMS U–Pb zircon analyses yielded ages of 1343 ± 27 Ma (MSWD = 0.3) and 1276 ± 22 Ma (MSWD = 0.4) for two granite gneisses, and a consistent age of ca. 1250 Ma for two biotite gneisses. These ages are interpreted as the magma crystallization time of both the gneisses protoliths, and thus the Bomi Complex represents the oldest rocks found in the Lhasa terrane. Our data indicate that the Mesoproterozoic detrital zircons from the Paleozoic metasedimentary rocks in the Lhasa terrane could be derived from the Lhasa terrane itself or the Tethyan Himalaya, rather than necessarily from the Albany-Fraser belt in the Australia. Geochemical characteristics show that the granite gneisses have an aluminous A-type granite affinity. The two granite gneisses dated in this study have zircon
εHf(t) values between +4.0 and +1.8 and between +2.6 and +0.2, respectively. They have identical twostage Hf model ages of ~2.0 Ga. We suggest that the protoliths of the granite gneisses were produced by protracted high temperature partial melting of a felsic intracrustal source in an extensional setting. In contrast, the biotite gneisses have similar geochemical characteristics to those of calc-alkaline granitoids that probably formed in a subduction-related environment. Zircons from the two dated biotite gneisses have relatively higher εHf(t) values of +8.1 to +3.6 and +10.5 to +5.7, respectively, indicating a juvenile mantle contribution to their magma source. Earlier magmatism at ~1343–1276 Ma may formed in a continental rift setting related to the final breakup of supercontinent Columbia, while subsequent magmatism of ~1250 Ma resulted from subduction of ocean slab during the assemblage of Rodinia. We thus infer that the Bomi Complex was related to the contact zone between the Eastern Ghats Belt and .the Archean cratons in southeastern India during the Mesoproterozoic

Item Type: Journal Item
Copyright Holders: 2013 Elsevier B. V.
ISSN: 0301-9268
Project Funding Details:
Funded Project NameProject IDFunding Body
Not SetGrants: 41103019 and 41073046Natural Science Foundation of China
National Key Project for Basic ResearchNo. 2011CB403102Not Set
Not SetNo. 1212011121261China Geological Survey
Not SetNot SetFundamental Research Funds for the Central Universities
Keywords: Mesoproterozoic; tectonic evolution; aluminous A-type granite; Bomi Complex; Lhasa terrane
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Environment, Earth and Ecosystem Sciences
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 38346
Depositing User: Nigel Harris
Date Deposited: 05 Sep 2013 11:00
Last Modified: 07 Dec 2018 17:33
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