Cambrian volcanism in the Lhasa terrane,southern Tibet: Record of an early Paleozoic Andean-type magmatic arc along the Gondwana proto-Tethyan margin |
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| Institution: | 1. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, No. 229, Northern Taibai Road, Xi''an 710069, Shaanxi, People''s Republic of China;2. College of Marine Geosciences, Ocean University of China, 266100 Qingdao, People''s Republic of China;3. College of Resources, Environment and Tourism, Capital Normal University, Beijing 100048, People''s Republic of China;4. Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia;1. College of Earth Science, Jilin University, Changchun 130061, China;2. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China;1. State Key Laboratory of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Science, No. 26 Baiwanzhuang Road, Beijing 100037, China;2. Geological Exploration Technology Institute of Jiangsu Province, Nanjing 210049, China;3. Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China |
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| Abstract: | The present study reports new zircon LA–ICP–MS U–Pb ages, trace element and Hf isotope data, and whole-rock major and trace element data from Cambrian metarhyolites from Zhaqian and Zhakang in the central Lhasa subterrane of southern Tibet. One sample from Zhakang provides a weighted mean 206Pb/238U age of 510.4 ± 4.0 Ma and two samples from Zhaqian yield weighted mean 206Pb/238U ages of 510.6 ± 2.6 Ma and 524.8 ± 2.9 Ma, indicating that the Zhaqian and Zhakang metarhyolites were contemporaneous. Both are characterized by high SiO2 and K2O and low Na2O. They are also primarily high-K calc-alkaline, are enriched in Th, U, and light rare earth elements (LREEs), and are depleted in Nb, Ta, Ti, and P. Thus, they are geochemically similar to typical arc volcanic rocks. Moreover, the Zhaqian metarhyolites exhibit varying zircon εHf(t) values (−3.8 to +0.3) that are comparable to those of the Zhakang metarhyolites (−4.9 to −1.0). Both metarhyolites are interpreted as resulting from partial melting of Proterozoic metasedimentary rocks with mantle-derived magma contributions. Contemporaneous magmatism in the early Paleozoic has also been recognized in other microcontinents along the Gondwana proto-Tethyan margin. The emplacement of these magmatic rocks and the development of a Cambro–Ordovician angular unconformity in the central Lhasa subterrane can be attributed to subduction of proto-Tethys Ocean lithosphere in a Andean-type magmatic arc setting following the assembly of various continental components within the Gondwana supercontinent. |
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| Keywords: | Whole-rock geochemistry Lhasa terrane Cambrian metarhyolite Andean-type magmatic arc |
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