The Pengguan tectonic dome of Longmen Mountains, Sichuan Province: Mesozoic denudation of a Neoproterozoic magmatic arc-basin system |
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Authors: | DanPing Yan MeiFu Zhou GuoQing Wei JianFeng Gao ShaoFeng Liu Ping Xu and XiaoYing Shi |
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Institution: | (1) State Key Laboratory of Geological Processes and Mineral Resources, Key Laboratory of Lithospheric Tectonics and Lithoprobing Technology of Ministry of Education, China University of Geosciences, Beijing, 100083, China;(2) Department of Earth Sciences, The University of Hong Kong, Hong Kong SAR, China |
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Abstract: | Neoproterozoic igneous and metamorphic complexes occur as tectonic domes in the Longmen Mountains of the western margin of
the Yangtze Block, and are important in reconstructing the Rodinian supercontinent and constraining the timing and mechanism
of tectonic denudational processes. The Pengguan dome consists of granitic intrusions and metamorphic rocks of the Huangshuihe
Group and is tectonically overlain by ductilly deformed Sinian to Paleozoic strata. The plutonic intrusions consist of granites
with abundant amphibolite enclaves. New LA-ICP-MS zircon U-Pb dating yielded an emplacement age of 809±3 Ma and a protolith
age of 844±6 Ma for the granite. The granitic rocks have geochemical signatures typical of A-type granites, indicating their
formation under an extensional environment, by melting of newly formed tonalite-trondhjemite-granodiorite (TTG) rocks. A detachment
fault, characterized by variable ductile shear deformation of S-C fabric and ESE-ward kinematics, separates the Pengguan dome
from the Sinian-Paleozoic cover. 40Ar/39Ar dating of muscovite from the mylonite in the detachment fault of the dome demonstrates that ductile deformation occurred
at ∼160 Ma. This study indicates the existence of a Neoproterozoic magmatic arc-basin system, which was denudated by a Jurassic
middle crustal ductile channel flow along the Longmenshan thrust belt.
Supported by NSFC Innovation Research Group Program (Grant No. 40621002), MOE Innovative Research Team Program (Grant No.
IRT0546), the National Natural Science Foundation of China (Grant No. 40472106), the “111” Project (Grant No. B07011), the
Project from China Petrochemical Corporation (09-01) and Committee on Research and Conference Grants of the University of
Hong Kong |
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Keywords: | Pengguan tectonic dome Neoproterozoic magmatic arc Mesozoic denudation |
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