Contrasting exhumation histories and relief development within the Three Rivers Region (south-east Tibet)

Abstract. The Three Rivers Region in south-east Tibet represents a transition between the strongly deformed zone around Eastern Himalayan Syntaxis (EHS) and less Tibetan Plateau margin Yunnan Sichuan. In this study, we compile model published thermochronometric ages for two massifs facing each other across Mekong River core of (TRR), using thermo-kinematic code Pecube to constrain their exhumation relief history. Modelling results low-relief (< 600 m), moderate-elevation (? 4500 m) Baima Xueshan massif, east River, suggest regional rock uplift at rate 0.25 km/Myr since ? 10 Ma, following slow 0.01 least 22 Ma. Estimated incision accounts 30 % total We interpret massif as response EHS conclude that low was acquired high elevation (> probably part due glacial “buzzsaw-like” processes active such particularly efficient during Quaternary glaciations. Exhumation is significantly higher (2.5 km Ma) than estimated most emblematic “relict” surfaces eastern Tibet, where apatite (U–Th) / He (AHe) > 50 Ma imply only few hundreds metres onset India–Asia collision. with its younger AHe record significant exhumation, thus cannot be classified relict surface. high-relief, high-elevation Kawagebo west Mekong, similar contribution (25 %) but much stronger local 0.45 accelerating 1.86 1.6 show are best reproduced by on kinked westward-dipping thrust striking roughly parallel steep shallow segment flattening out depth. Thus, strong differences linked variable histories differing tectonic imprint.