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A syn-collisional model for Early Cretaceous magmatism in the northern and central Lhasa subterranes
Author: Chen, S. S., R. D. Shi, X. H. Gong, D. L. Liu, Q. S. Huang, G. D. Yi, K. Wu and H. B. Zou
Abstract: Voluminous Early Cretaceous volcanic rocks from the northern and central Lhasa subterranes contain important information on the tectono-magmatic processes. In this contribution, we focus on the Lower Cretaceous volcanic rocks in the Nagqu area, northern Lhasa subterrane, and present their zircon LA-ICP-MS U-Pb ages, in situ Hf isotopic data, whole-rock major and trace element compositions, and Sr-Nd isotopic data. The Nagqu volcanic rocks are high-K calc-alkaline to shoshonitic (K2O: 1.41-8.52 wt.%; K2O/Na2O: 0.36-6.65) and feature similar geochemical characteristics (e.g., subparallel distribution of incompatible elements and REEs). Assimilation-fractional crystallization of magmas from identical source (rather than diverse magma sources) was mainly responsible for the formation of the diverse volcanic rock types. High Hf/Sm (>0.7) and high U/Yb whole-rock values and low Y values in zircon grains suggest the involvement of terrigenous components rather than subducted oceanic crust in the magma source. Tectonic discrimination diagrams, sedimentary environment (marine-continental transition), magma compositions (K-rich and terrigenous components), crustal thickening, and spatio-temporal variations in subduction, syn-collisional and post-collisional processes, indicate that the geodynamic setting of the Early Cretaceous magmatism was associated with the collision between the Lhasa and Qiangtang terranes. The high-K characteristics were inherited from the melts derived from the partial melting of lower metasomatized lithosphericmantle (the K-rich layer), which was transported to great depths by the continuously thickening lithosphere, eventually triggering melting. (C) 2015 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
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Page number: 93-109
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PubYear: 2017
Volume: 41
Publication name: Gondwana Research
Abstract: Voluminous Early Cretaceous volcanic rocks from the northern and central Lhasa subterranes contain important information on the tectono-magmatic processes. In this contribution, we focus on the Lower Cretaceous volcanic rocks in the Nagqu area, northern Lhasa subterrane, and present their zircon LA-ICP-MS U-Pb ages, in situ Hf isotopic data, whole-rock major and trace element compositions, and Sr-Nd isotopic data. The Nagqu volcanic rocks are high-K calc-alkaline to shoshonitic (K2O: 1.41-8.52 wt.%; K2O/Na2O: 0.36-6.65) and feature similar geochemical characteristics (e.g., subparallel distribution of incompatible elements and REEs). Assimilation-fractional crystallization of magmas from identical source (rather than diverse magma sources) was mainly responsible for the formation of the diverse volcanic rock types. High Hf/Sm (>0.7) and high U/Yb whole-rock values and low Y values in zircon grains suggest the involvement of terrigenous components rather than subducted oceanic crust in the magma source. Tectonic discrimination diagrams, sedimentary environment (marine-continental transition), magma compositions (K-rich and terrigenous components), crustal thickening, and spatio-temporal variations in subduction, syn-collisional and post-collisional processes, indicate that the geodynamic setting of the Early Cretaceous magmatism was associated with the collision between the Lhasa and Qiangtang terranes. The high-K characteristics were inherited from the melts derived from the partial melting of lower metasomatized lithosphericmantle (the K-rich layer), which was transported to great depths by the continuously thickening lithosphere, eventually triggering melting. (C) 2015 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
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