Petrology and geochronology of the Namche Barwa Complex in the eastern Himalayan syntaxis, Tibet: Constraints on the origin and evolution of the north-eastern margin of the Indian Craton |
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| Authors: | Zeming Zhang Xin DongM Santosh Feng LiuWei Wang Fei YiuZhenyu He Kun Shen |
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| Institution: | a Key Laboratory of Continental Dynamics, Institute of Geology, Chinese Academy of Geological Science, No. 26 Baiwanzhuang Road, Beijing 100037, Chinab State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, Chinac Division of Interdisciplinary Science, Faculty of Science, Kochi University, Akebono-cho, Kochi 780-8520, Japand Graduate School, China University of Geosciences, Wuhan, 430074, Chinae Institute of Geological Sciences of Shandong, Jinan 250013, China |
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| Abstract: | The Namche Barwa Complex (NBC) in the eastern Himalayan syntaxis, south Tibet, is generally interpreted as the north-eastern extremity of the exposed Greater Himalayan Sequence, comprising Neoproterozoic to early Paleozoic sedimentary strata along the northern margin of the Indian continent. Field and petrological investigations indicate that the NBC consists mainly of orthogneiss, paragneiss, amphibolites and calc-silicate rocks. U-Pb zircon data demonstrate that the protoliths of the orthogneiss formed during late Paleoproterozoic at ca. 1610 Ma and also in early Paleozoic at ca. 490-500 Ma. The amphibolites were derived from mafic magmatic rocks formed during 1645 to 1590 Ma. Zircons in the paragneisses have highly variable inherited zircon ages ranging from the Neoarchean to early Paleozoic, with four major age populations of 2490 Ma, 1640 Ma, 990 Ma and 480 Ma. The calc-silicate rock has zircons with early Paleozoic metamorphic age of 538 Ma. Almost all the rocks of the NBC have been metamorphosed during Cenozoic with the metamorphic zircon U-Pb ages ranging from 8 to 30 Ma and a peak at 23 Ma. These, together with previous results suggest that the NBC was originally derived from an Andean-type orogeny following the Columbia supercontinent assembly, and experienced multiple reworking during the Grenvillian, Pan-African and Himalayan orogenies. We conclude that the NBC in the eastern Himalayan syntaxis was derived from different provenance and tectonic setting as compared to those of the Greater Himalayan Sequence which constitutes the high-grade metamorphic core of the western and central Himalayan orogenic belt. We thus infer that the NBC was originally part of the eastern segment of the Central Indian Tectonic Zone. |
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| Keywords: | Petrology and geochronology Multiple magmatism and metamorphism Namche Barwa Complex Eastern Himalayan syntaxis South Tibet |
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