Southwestward growth of plateau surfaces in eastern Tibet

Both the kinematics and dynamics of topographic growth of the Tibetan Plateau remain debated, despite their significance for understanding the evolution of continental lithospheric geodynamics, climate, and biodiversity in Asia. Topographic swath profiles reveal the diversity of high-elevation, low-relief plateau surfaces or “relict landscapes” throughout the southeast Qiangtang, northeast Qiangtang, and Songpan-Garze-Yidun terranes in eastern Tibet, including the Zuogong, Markam, Litang, and Kangding plateaux from southwest to northeast. New geo-thermochronology data combined with morphotectonic analysis of the Qiangtang terrane underscore that the Lancangjiang thrust belt, separating the Zuogong and Markam plateaux, is a prominent tectonic and geomorphic boundary that limits high topography at mean elevations of >5000 m around the eastern Himalayan syntaxis. Inverse thermal-history modelling of thermochronological data reveals accelerated cooling at 40–35 Ma at rates of 1.2 ± 0.4 mm/yr in the Zuogong plateau and contemporaneous slow cooling of 0.10 ± 0.02 mm/yr in the Markam and Weixi plateaux in eastern Tibet, which is interpreted as recording activity of the Lancangjiang and Markam fold-and-thrust belts. These data, together with coeval cooling signals in the central and southeast Qiangtang terrane, indicate widespread crustal shortening and thickening throughout the terrane that likely led to surface uplift to near-present-day elevations by the late Eocene. Very slow cooling at a rate of <0.5 °C/Myr rules out significant tectonically-driven surface uplift and erosion of the Markam plateau since then. A second stage of rapid exhumation at ca. 20 Ma, at rates of 1.0–1.3 mm/yr, in the Zuogong plateau in the hanging wall of the Lancangjiang thrust, sharply contrasts to exhumation rates of 0.02 mm/yr for the Markam plateau in the footwall and suggests reactivation of the Lancangjiang thrust belt at that time. The transition to slow denudation after ca. 20 Ma for the Zuogong plateau in the southwest Qiangtang suggests tectonic and topographic stabilization of this low-relief surface at least 15–20 Myr later than the Markam plateau. In contrast, a compilation of existing low-temperature thermochronology data in the Songpan-Garze-Yidun terranes shows much older ages for stabilization of the low-relief surfaces in the Litang and Kangding plateaux by 80–60 Ma. We thus suggest that tectonic and topographic stabilization of plateau surfaces in eastern Tibet has occurred at 80–60 Ma, 40–35 Ma, and ~ 20 Ma in the Songpan-Garze-Yidun, northeast Qiangtang, and southwest Qiangtang, respectively. The southwestward piecemeal expansion of small plateaux suggests that the high-elevation, low-relief landscape of eastern Tibet has been constructed during distinct orogenic episodes prior to and during the early stages of India-Asia collision. A late stage of tectonic activity related to northward indentation of the Indian plate during the Neogene mostly remodeled the outer rims of the plateaux and the valleys that delineate transcurrent faults, while drainage expansion and integration triggered river incision in eastern Tibet.