Isotopic and structural constraints on the late Miocene to Pliocene evolution of the Namche Barwa area,eastern Himalayan syntaxis,SE Tibet |
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| Authors: | Yan Liu Wolfgang Siebel Thomas Theye Hans-Joachim Massonne |
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| Institution: | 1. Department of Geological Engineering, Karadeniz Technical University, 61080, Trabzon, Turkey;2. State Key Laboratory of Geological Processes and Mineral Resources, and School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China;3. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA;4. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;1. Department of Earth & Environmental Sciences, 227 Hutchison Hall, University of Rochester, Rochester, NY 14627, USA;2. INSA Honorary Scientist, 103, Sector 7, Panchkula, Haryana 134109, India;3. Department of Geology, Banaras Hindu University, Varanasi, UP 221005, India;4. Department of Geology, Panjab University, Sector-14, Chandigarh-160014, India;1. State Key of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Department of Earth Sciences, the University of Hong Kong, Pokfulam Road, Hong Kong, China;4. State Key Laboratory of Ore Deport Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002, China |
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| Abstract: | Within the Namche Barwa area, SE Tibet, the Indus–Yarlung suture zone separates the Lhasa terrain in the north from the Himalayan unit including the Tethyan (sedimentary and volcanic rocks), Dongjiu (greenschist to lower amphibolite facies), Namche Barwa (granulite facies), Pei (amphibolite facies) and Laiguo (greenschist facies) sequences in the south. Two fault systems were distinguished in the Namche Barwa area. The former includes a top-down-to-the-north normal fault in the north and two top-to-the-south thrust zones in the south named as Upper and Lower Thrusts, respectively. The Namche Barwa and Pei sequences were exhumed southwards from beneath the Dongjiu sequence by these faults. Thus, the fault system is regarded as a southward extrusion structure. Subsequently, the exposed Dongjiu, Namche Barwa, Pei and Laiguo sequences were displaced northwards onto the Lhasa terrain by the top-to-the-north fault system, thus, marking it as northward indentation structure. Monazite TIMS U–Pb dating demonstrates that the normal fault and the Lower Thrust from the southward extrusion system were probably active at ~ 6 Ma and ~ 10 Ma, respectively. Zircon U–Pb SHRIMP and phlogopite K–Ar ages further suggest that the Upper Thrust was active between 6.2 ± 0.2 Ma and 5.5 ± 0.2 Ma. The northward indentation structures within the core portion of the eastern Himalayan syntaxis were perhaps active between 3.0 Ma and 1.5 Ma, as inferred by published zircon U–Pb SHRIMP and hornblende Ar–Ar ages. The monazite from upper portions of the Pei sequence dated by U–Pb TIMS indicates that the precursor sediments of this sequence were derived from Proterozoic source regions. Nd isotopic data further suggest that all the metamorphic rocks within eastern Himalaya (εNd = ? 13 to ? 19) correlate closely with those from the Greater Himalayan Sequences, whereas the western Himalayan syntaxis is mainly comprised of Lesser Himalayan Sequences. The two indented corners of the Himalaya are, thus, different. |
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