High-pressure metamorphism in Taiwan: from oceanic subduction to arc-continent collision?

The Taiwan orogen has been the focus of a number of models of mountain building processes, but little attention has been paid to high-pressure (HP) metamorphic rocks that are found as exotic blocks intermingled within the deepest units of the mountain belt. In this study, we re-appraise from updated petrological and thermodynamic databases the physical conditions of HP metamorphism in Taiwan, and we combine our findings with available geochronological data to estimate the thermal history of these rocks. Our results indicate that peak metamorphic conditions of 550 C and 10–12 kbar have been followed by a rapid isothermal decompression, with exhumation possibly as rapid as burial. These units have subsequently been stored at a pressure of 3 kbar for 4–5 Myr, before their final exhumation, probably facilitated by the accretion of passive margin sequences during the Late Cenozoic collision. Therefore, HP units in Taiwan maintain a record of processes at depth from the early stages of oceanic subduction to the present arc-continent collision.