Extraordinary denudation in the Sichuan Basin: Insights from low-temperature thermochronology adjacent to the eastern margin of the Tibetan Plateau

摘要

The eastern margin of the Tibetan Plateau combines very high relief with almost no Tertiary foreland sedimentation and little evidence of Cenozoic tectonic shortening. While river incision and landscape development at the plateau margin have received significant attention over the last decade, little is known about the Cenozoic development of the adjacent Sichuan Basin. Here we assess the Cenozoic thermal history of this basin using detrital apatite fission track (AFT) and (U-Th)/He techniques and establish the presence of an exhumed AFT paleopartial annealing zone across much of the basin. This observation, combined with stratigraphic and borehole sections and inverse modeling of confined apatite fission tracks, indicates that the strata within the basin have undergone accelerated cooling after ～40 Ma, consistent with the widespread erosion of ～1 to 4 km of overlying sedimentary material. This regional-scale erosion is most likely a response to changes in the Yangtze River system draining and removing sediment from the basin. The base-level fall associated with this erosion contributed to a relative increase in relief across the Longmen Shan and may have helped drive Miocene-Recent incision and unloading of the plateau margin.