Damage asymmetry of the Chimei Fault, eastern Taiwan, and implications for deformation evolution

The mesoscale deformation structures in eastern Taiwan are considered to have recorded progressive deformation during rapid convergence and uplift in response to arc-continent collision. However, detailed deformation mechanisms and kinematic history of faulting remained poorly known. The Chimei Fault in eastern Taiwan thrusts the igneous forearc basement over the orogen-derived turbidites, and its outcrops provide opportunities to understand deformation mechanisms of the fault rocks across a bi-material fault during the arc-continent collision. To unravel the structural and mechanical architecture of the Chimei Fault, we performed field observations, paleostress analysis, and fold analysis. The Chimei Fault shows a fault core surrounded by damage zones. The width of the damage zones across the fault core is asymmetric, with the footwall turbidites exhibiting wider damage zone with higher fracture intensity than the hanging wall andesitic complex. Our paleostress analysis reveals that the mechanically stronger hanging wall can accommodate larger differential stress than the weaker footwall. Different deformation styles in the footwall damage zones, including pinch-and-swell structures, boudins, and postdating fractures, suggesting progressive deformation while sediment lithification in response to the activities of the Chimei Fault.