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Thrusting, exhumation and basin fill on the western margin of the South China block during India-Asian collision
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  • Kai Cao,
  • Guocan Wang,
  • Philippe Hervé Leloup,
  • Wei Mahéo,
  • Yadong Xu,
  • Kexin Zhang
Kai Cao

Corresponding Author:kai.cao@cug.edu.cn

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Guocan Wang
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Philippe Hervé Leloup
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Wei Mahéo
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Kexin Zhang
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The pattern and timing of deformation in the southeast Tibet resulting from the India-Asian collision remain poorly constrained. Detailed field mapping, structural analysis and geo-thermochronogic data within a newly-defined Ludian-Zhonghejiang fold-thrust belt stretching over 120 km between the Diancang Shan and Xuelong Shan metamorphic belt in western Yunnan, China document Early Cenozoic tectonic evolution of the conjunction area between the Lanping-Simao and South China blocks. The study area is cut by two major northwest-striking, southwest-dipping brittle faults, named Ludian-Zhonghejiang fault and Tongdian fault from east to west. Kinematic measurements and indicators of S-C fabrics and striations, as well as juxtaposition of Triassic meta-sedimentary rocks overlying on Paleocene strata indicate thrusting along the Ludian-Zhonghejiang fault. Similarly, structural analysis show the Tongdian fault is also a reverse fault. Between these structures, fault-bounded Permo-Triassic and Paleocene strata are strongly deformed by upright southwest-vergent folds with axes that trend nearly parallel to the traces of the principal faults, consistent with reserve faulting related to regional NE-oriented compression. Zircon and apatite (U-Th)/He and apatite fission track ages from a Triassic granitic pluton in the hanging wall of the Ludian-Zhonghejiang thrust assisted by inverse modeling reveal a period of accelerated cooling from 50 Ma to 37 Ma, which is interpreted to record the lifespan of the fold-thrust system collaborated by the intrusive relations between magmas of ~35 Ma dated by zircon U-Pb and the fold and thrust belt. Since 37 Ma, decreasing cooling rates implies cessation of the thrusting. Early Cenozoic activity of the deformation system likely controlled deposition of the Jianchuan-Liming basin evident by coeval sediments derived from the proximal hanging wall of the fold-thrust belt. These results, together with tectonic records of contraction in east Tibet, suggest crustal shortening related to the India-Asian collision and convergence prevailed the southern and eastern part of the Tibetan Plateau, which predated Oligo-Miocene onset of extrusion tectonics in southeast Tibet.