Late Miocene accelerated exhumation of the Daliang Mountains, southeastern margin of the Tibetan Plateau

Abstract

The Late Cenozoic evolution of the southeastern margin of the Tibetan Plateau has been well documented, but controversies remain concerning Late Cenozoic acceleration of exhumation. We present 41 new apatite and zircon (U–Th)/He ages from six transects in the Daliang Mountains that provide constraints on the timing and the rate of denudation. We calculated exhumation rates for the transects based on the age versus elevation/structural depth relationship. The results are consistent across the Daliang Mountains and indicate a protracted period of slow cooling and denudation from ~30 to ~10 Ma, with an exhumation rate of ~0.15 mm/year. This slow exhumation is followed by accelerated rates of ~0.4–0.8 mm/year since ~10 Ma. The protracted slow denudation and long residence time within the apatite helium partial retention zone resulted in large variations in single-grain (U–Th)/He ages. We suggest that the post ~10-Ma rapid cooling and exhumation in the Daliang Mountains is driven by the eastward growth of the Tibetan Plateau. Furthermore, we suggest that the mountain building in the Daliang Mountains result from the crustal shortening accompanied with transpression, rather than from the lower crustal channel flow.