Rapid topographic growth of the Diancang Shan, southeastern margin of the Tibetan Plateau since 5.0–3.5 Ma

Abstract. As a crucial geological, climatic, and ecological boundary in the southeastern margin of the Tibetan Plateau (SEMTP), the topographic evolution of the Diancang Shan (DCS) remains unclear due to the lack of direct constraints on its paleoelevation. Here, we quantitatively reconstructed changes in annual mean temperature (ANNT) based on palynological data from the terrestrial Dasongping section (~7.6–1.8 Ma) in the Dali Basin, located at the northeastern margin of the DCS in Yunnan Province, China. Integrating the thermochronological data from the eastern and southern margins of DCS, we have clarified the paleotopographic evolution of DCS during this period: the paleoelevation of DCS likely exceeded 2000 meters above sea level (m a.s.l.) due to initial normal faulting at ~7.6 Ma, possibly comparable to the current average elevation (~2200 m a.s.l.) of surrounding Dali Basin region. Significant growth occurred between ~5.0 Ma and ~3.5 Ma, with at least ~1000 meters uplift gain in the northern segment and up to ~2000 meters in the southern segment of DCS, caused by the intensification of normal faulting activities. Finally, the northern segment of DCS reached the elevation of ~3500 m a.s.l. after ~1.8 Ma. Our findings suggest that the quantitively ANNT reconstruction, combined with thermochronological and sedimentary data, can significantly improve constraint on the paleotopographic evolution of DCS.