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

P. H. Leloup,1 N. Arnaud,2 R. Lacassin,1 J. R. Kienast,3 T. M. Harrison,4 T. Phan Trong,5 A. Replumaz,1 and P. Tapponnier1

Abstract. New structural, petrographic, and 40Ar/39Ar data constrain the kinematics of the ASRR (Ailao Shan­Red 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 re-sumed 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 decompres-sion from 6.5kbar during left-lateral shear (temperatures >700°C). 40Ar/39Ar data imply rapid cooling from above 350°C to below 150°C 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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Déformation de la lithosphère continentale. Exemple de l'Asie du SE au Tertiaire

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How does the continental lithosphere deform ?
Insigths from Tertiary deformation of SE Asia