A new interpretation of the metamorphic core in the Taiwan orogen: A regional-scale, left-lateral shear zone that accommodated highly oblique plate convergence in the Plio-Pleistocene

In the past decades, the arc-continent collision in Taiwan was commonly interpreted as a relatively continuous process with an invariant plate convergence vector for at least the last 6–5 Ma. This steady convergence, including the rate and the obliquity, between the subducting continental margin and the plate boundary suggest a propagating collision with a space-time equivalence along the developing orogen. More recently, detailed low-temperature geochronologic and plate reconstructions suggest that the plate convergence changed from highly oblique to nearly orthogonal in the last 2 to 1 Ma. This early phase of oblique convergence, driven primarily by the northward motion of the Philippine Sea Plate wrt the Eurasian Plate, implies a significant ‘fossil’ component of left-lateral, strike-slip motion along the presumably north-trending plate boundary. A synthesis of available data compiled in this study suggests that previously uncharacterized zones of strike-slip deformation exist in the Tailuko Belt, and here we document: 1) the distribution of horizontal shear, 2) the kinematics of deformation, 3) the age of deformation, and 4) regional consistency between geologic studies and plate reconstructions. Horizontal shear may also be recorded at shallow structural levels in southern Taiwan by brittle faults and block rotations. Integration of these new data with previously published kinematic data across strike also suggests plate convergence was partitioned with strike-slip motion in the retrowedge (i.e., the Tailuko Belt) and shortening in the prowedge (i.e., the Slate Belt).