Late Eocene-Early Oligocene Eastward Growth of the Tibetan Plateau: Insights from Crustal Shortening of the Sichuan Basin

The effect of the eastward growth of the Tibetan Plateau on the morphotectonic evolution of South China is still a matter of debate. Here, we report new apatite fission track, apatite (U-Th-Sm)/He and zircon (U-Th)/He dates and analog model reconstruct the Mesozoic-Cenozoic tectonic evolution of the southeastern Sichuan fold-thrust belt (SS-FTB), on the eastern margin of the Tibetan Plateau. Combined interpretation of thermochronology data and results of analog modeling show that the SS-FTB experienced an early northwestward progressive deformation between 100 Ma and 80 Ma forming several large-scale anticlines. A later accelerated cooling initiated between ∼35 Ma and 20 Ma, identified across the belt, implies that a crustal shortening and exhumation since the late Eocene-early Oligocene may have been widespread along the Sichuan Basin. This latter exhumation was a response to the far-field effect of the eastward growth of the Tibetan Plateau, which is accounted for the counterclockwise rotation axes of pre-existing anticlines and formation of a younger anticlines, hence the curved geometry of the belt.