Miocene high‐elevation landscape of the eastern T ibetan P lateau

The high topography of central Asia is the most distinctive expression of the India‐Asia collision, yet a broad understanding of the timing and processes involved in the development of the Tibetan Plateau remains elusive. Here we investigate the Neogene Songpan Basin located on the eastern margin of the plateau using oxygen isotope paleoaltimetry to determine when the steep Longmen Shan margin obtained its present elevations. Hydrologically open lacustrine and fluvial‐alluvial authigenic carbonates from the basin record the paleoelevations of the eastern Tibetan Plateau and suggest that the area has attained near‐present elevations of ∼3000 m by the late Miocene. This reconstruction is consistent with the results from the comparison of pollen fossils to their nearest living relatives in this area (2750–3050 m). We propose that the eastern Tibetan Plateau may have attained significant elevations prior to the late Miocene through an uplift scenario involving eastward growth of the plateau between the Eocene and the Miocene. Two tectonic processes, either crustal shortening in the Oligocene‐Miocene or eastward propagation of weakened lower crust starting in the Eocene, most likely thickened the crust and raised the surface of the eastern Tibetan Plateau to its present elevation by the late Miocene.