Pliocene onset of rapid exhumation in Taiwan during arc-continent collision: new insights from detrital thermochronometry

The Coastal Range in eastern Taiwan contains the remnants of the Pliocene-Pleistocene retro-foredeep basin of the ongoing Penglai orogeny. These sedimentary successions record the earliest exhumation of the Central Range, Taiwan. We dated detrital Plio-Pleistocene sediments in the Coastal Range using multiple thermochronometers [fission-track, zircon (U-Th)/He and U/Pb dating] to document changes in exhumation rate through time. Fission-track grain ages in 2-4-Myr-old sediments were not reset by the Penglai orogeny and reflect the early stage removal of the sedimentary cover. This early stage, when exhumation rates were low, could encompass both the accretionary wedge phase of the orogen and the early arc-continent collision. Sediments younger than 2-Myr-old yield Pliocene zircon fission-track grain ages and suggest that exhumation, transport and deposition occurred within 0.4-1.5 Myr. The recorded onset of rapid exhumation in the Pliocene is contemporaneous with other major tectonic changes in the region, including an increase in subsidence rate in both the pro- and retro-foredeep basins and a change in the wedge kinematics from internal shortening to underplating.