Thermomechanical models of the arc-continent collision in Taiwan

The Taiwan orogeny represents a prime example of arc-continent collision, characterized by complex geological structures, rapid exhumation, and dynamic deformation. To elucidate these processes, we developed advanced thermomechanical models incorporating key physical mechanisms: chlorite dehydration, mantle hydration, mantle wedge partial melting, magma migration, magma latent heat, and elasto-visco-plastic rheology.

Our simulations reveal critical insights into the collision dynamics. When the subducting plate transitions from oceanic to continental crust, the lower density of continental crust inhibits subduction. The resulting orogenic mass deflects the Philippine Sea plate, causing the forearc crust to buckle and form a forearc basin. This basin accumulates substantial sedimentary material over time. As the basin matures, extension in its center creates a fault, allowing the arc and its basement rocks to thrust over the forearc sediments. This thrusting drives rapid uplift of the basin fill and ultimately causes the forearc basement to subduct beneath the Philippine Sea plate.

This integrated model explains several first-order observations: the absence of the original forearc basement, the seismicity patterns, the timing of Longitudinal Valley fault initiation, and the dramatic vertical motions preserved in the Coastal Range sedimentary record. By linking mantle processes to surface deformation, our results provide a mechanistic explanation for the extreme topography and rapid strain accumulation characteristic of Taiwan's collision zone.