Southwestward growth of plateau surfaces in eastern Tibet

Abstract

Both the kinematics and dynamics for topographic growth of the Tibetan Plateau remain debated despite their significance for understanding the evolution of continental lithospheric geodynamics, climate, and biodiversity in Asia. Morphometric analysis reveals the continuity of high-elevated peneplains through the Songpan-Garze-Yidun, Qiangtang and Lhasa terranes in eastern Tibet. Inverse thermal-history modeling of thermochronological data indicates slow cooling of these terranes since 80-60 Ma, 40-35 Ma and 20-5 Ma, respectively, which is interpreted as marking tectonic and topographic stabilization of the plateau surfaces. The diachronous stabilization of flat plateau surfaces and early encroachment suggests decoupling of plateau surface formation from Neogene river incision and tectonics. This southwestward piecemeal expansion of small plateaus suggests that the high-elevation, low-relief landscape of eastern Tibet has been constructed during distinct orogenic episodes prior and during the early stages of India-Asia collision. A late stage of tectonic activity during Neogene only moderately remodeled the outer rims of the plateaus and the valleys that delineate the transcurrent faults, while lower crustal channel flow only leveled the distinct plateaus to a unique elevation, thereby triggering river incision in eastern Tibet.