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New constraints on the structure, thermochronology, and timing of the Ailao Shan-Red River shear zone, SE Asia

Abstract : New structural, petrographic, and 4øAr/39Ar data constrain the kinematics of the ASRR (Ailao Shan-Red River shear zone). In the XueLong Shan (XLS), geochronological data reveal Triassic, Early Tertiary, and Oligo-Miocene thermal events. The latter event (33-26Ma) corresponds to cooling during left-lateral shear. In the FanSiPan (FSP) range, thrusting of the SaPa nappe, linked to left-lateral deformation, and cooling of the FSP granite occurred at-35Ma. Rapid cooling resumed at 25-29Ma as a result of uplift within the transtensive ASRR. In the DayNuiConVoi (DNCV), foliation trends NW-SE, but is deflected near large-scale. shear planes. Stretching lineation is nearly horizontal. On steep foliations, shear criteria indicate left-lateral shear sense. Zones with flatter foliations show compatible shear senses. Petrographic data indicate decompression from-6.5kbar during left-lateral shear (temperatures >700øC). 4ømr/39Ar data imply rapid cooling from above 350øC to below 150øC between 25 and 22Ma without diachronism along strike. Along the whole ASRR cooling histories show two main episodes: (1) rapid cooling from peak metamorphism during left-lateral shear; (2) rapid cooling from greenschist conditions during right-lateral reactivation of the ASRR. In the NW part of the ASRR (XLS, Diancang Shan), we link rapid cooling 1 to local denudations in a transpressive environment. In the SW part (Ailao Shan and DNCV), cooling 1 resulted from regional denudation by zipper-like tectonics in a transtensive regime. The induced cooling diachronism observed in the Ailao Shan suggests left-lateral rates of 4 to 5 cm/yr from 27Ma until-17Ma. DNCV rocks always stayed in a transtensive regime and do not show cooling diachronism. The similarities of deformation kine-matics along the ASRR and in the South China Sea confirms the causal link between continental strike-slip faulting and marginal basin opening.
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P.H. Leloup, N. Amaud, R. Lacassin, J. R. Kienast, T. M. Harrison, et al.. New constraints on the structure, thermochronology, and timing of the Ailao Shan-Red River shear zone, SE Asia. Journal of Geophysical Research, American Geophysical Union, 2001, 106 (B4), pp.6683-6732. ⟨10.1029/2000JB900322⟩. ⟨insu-01891116⟩



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