Tectonothermal evolution of the eastern Tibetan Plateau Foreland: Fission-track thermochronology of the southern Dabashan fold-thrust belt

Apatite fission-track dating and thermal-history modeling were carried out on samples from the Dabashan (大巴山), a fold-thrust belt, northeast of the Sichuan (四川) Basin and east of the Tibetan Plateau. A first cooling event in the Late Cretaceous is followed by a prolonged period of thermal stability with exhumation rates of ≤0.025 mm/a, as determined from age vs. elevation relationships. The preservation of age vs. elevations relationships and the lack of distinct age changes across tectonic structures indicate that the Dabashan fold-thrust belt formed prior to the Late Cretaceous, consistent with the current view of Triassic-Early Cretaceous shortening. Relatively short mean track lengths (∼12 μm) indicate that the samples remained in the partial annealing zone for a prolonged time. The knick points in the best-fitting temperature-time models suggest that the onset of late-stage accelerated cooling commenced at ≤11 Ma. Related exhumation rates are 0.3–0.2 mm/a assuming geothermal gradients of 20 and 30 °C/km. We speculate that this late-stage event results from eastward growth of the Tibetan Plateau and overstepping of the Sichuan Basin, it is likely responsible for the youthful morphology of the Dabashan.