Late Cryogenian magmatic activity in the North Lhasa terrane,Tibet: Implication of slab break-off process |
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| Institution: | 1. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi''an 710069, China;2. Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;3. Department of Earth Sciences, University of HongKong, Pokfulam Road, Hong Kong, China;1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;3. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;4. College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 10049, China;5. School of Geosciences, The University of Sydney, NSW 2006, Australia;6. Institute of Geology and Geophysics, Chinese Academy of Science, Beijing 100029, China;1. Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;1. State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;2. Department of Environmental, Earth and Ecosystems, The Open University, Milton Keynes MK7 6AA, UK |
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| Abstract: | The North Lhasa terrane in Tibet is generally interpreted to be paleotectonically unrelated to the East African Orogen (EAO) and is instead thought to have derived from northeastern India or northwestern Australia. In this study, we present petrogenetic and geochronological results pertaining to the analysis of gabbros (ca. 652 Ma), diorites (ca. 658 and 646 Ma), and tonalites (ca. 652 Ma) from the North Lhasa terrane. The gabbros are calc-alkaline and exhibit arc-like geochemical features. Low positive zircon εHf(t) values (+1.0 to +3.8), high zircon δ18O (6.25‰ to 7.94‰), and low negative whole-rock εNd(t) values (?3.5 to ?1.4) indicate that the gabbros were derived from the lithospheric mantle, with geochemical modification by a subduction component. The diorite suite is characterized by a wide range of whole-rock chemistries (e.g., SiO2 = 51.33–61.98 wt%) and Hf–O–Sr isotopic compositions (εHf(t) = ?10.8 to ?0.1; δ18O = 5.17‰ to 7.11‰; ISr = 0.706 to 0.710), and negative whole-rock εNd(t) values (?7.0 to ?4.7). These diorites are geochemically similar to OIB and are interpreted to be products of the partial melting of a relatively deep mantle source (>85 km) prior to extensive modification by continental crustal material. The tonalites are adakitic and have moderate Mg# values (47–54), low compatible element abundances, positive zircon εHf(t) values (+3.4 to +6.2), high ISr values (0.714 to 0.715), and small negative whole-rock εNd(t) values (?1.6 to ?0.4). These tonalites most likely formed by the melting of thickened Mesoproterozoic continental crust. The generation of these ca. 650 Ma magmatic rocks was related to slab break-off in a collision zone. By integrating the findings of previous studies with the data of the present study, we suggest that the North Lhasa terrane was most likely located in the northern segment of the EAO in paleotectonic reconstructions of the Gondwana supercontinent. |
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