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Multiple Palaeozoic–Mesozoic orogenic events in the SE Yangtze Block, China: evidence from the petrogenesis and deformation of gneissic granites from the Nanwenhe metamorphic dome and regional correlation analysis

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posted on 24.11.2022, 07:20 authored by Xinming Zhang, Da Zhang, Jinbo Pan, Minfeng Bi, Ganguo Wu, Xiaolong He, Bojie Hu, Chaoyang Que, Yongjun Di, Wei Xue

The Nanwenhe metamorphic dome contains a rare Silurian granitic pluton that developed in the SE Yangtze Block during early Palaeozoic orogenesis, and this pluton comprises the Nanwenhe gneissic granites. The petrogenetic and structural deformation histories of the gneissic granites recorded the multi-stage interaction of the SE Yangtze Block with other blocks during the Palaeozoic and Mesozoic, including the Cathaysia, Indochina, and Paleo-Pacific blocks. Zircon U–Pb and Hf isotopes and geochemical data indicate that the Early Palaeozoic granites (433–420 Ma) are S-type granitic rocks, and they were derived from the partial melting of ancient continental crust with no contribution from mantle material. And the large variations and positive values of εHf(t) (−12.25 to +10.69) of the gneissic granites are ascribed to a heterogeneous source and disequilibrium melting. Here we compare early Palaeozoic granitoids in the SE Yangtze Block (foreland belt) with those in the orogenic core, and suggest that the SE Yangtze Block underwent limited syn-collisional crustal thickening and metamorphism, and following which post-collisional granitoids were formed through partial melting of continental crust. Structural analysis of the Nanwenhe gneissic granites allows two stages of deformation to be identified: northward detachment (D1) and northwestward thrusting (D2). 40Ar–39Ar isotope dating of muscovites from the gneissic granites yields a well-defined plateau age of 229.61 Ma, which is interpreted as the timing of Late Triassic structural overprinting associated with the formation of the Nanwenhe metamorphic dome. Integration of our new results with previous research findings from the dome and South China allows us to conclude that the detachment deformation (D1) represents Late Triassic post-collisional extension, and D2 represented Jurassic intracontinental orogeny associated with subduction of the Paleo-Pacific Block.

Funding

This work was supported by the National Key Research and Development Program of China [2016YFC0600509]; National Natural Science Foundation of China [41772069]. We appreciate Malipo County Government and Malipo Zijin Tungsten Industry Group for their support during fieldwork.

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