Mountain building in Taiwan: A thermokinematic model

Taiwan is a case example of a collisional orogen. This example has inspired in particular the most popular critical wedge model of mountain-building. This model seems irreconcilable with available data on the metamorphic history of the range, including new data from peak metamorphic temperatures measured from RSCM thermometry and (U-Th)/He cooling ages. In addition it seems that most of (if not all) the a39.5 to 44.5 mm/yr of shortening across the range are taken up by localized thrusting on the major frontal faults within the western foothills. This is also in contrast with the previous idea that the prism would undergo distributed shortening so as to maintain its critical taper. These various data are used here to develop an alternative thermo-kinematic model of the Taiwan orogen. In this model, the pre-Tertiary basement within the Tananao Complex has been uplifted as a result of sustained underplating at the base of the wedge and has been exhumed at a rate of a6.3 mm/yr, with no significant diachronism from north to south; the flux of underplated material beneath TC seems to have increased significantly ~ 1.5 Ma ago. The Hsueshan Range, further west, is another area where sustained uplift due to underplating is taking place with uplift rates of ~4.2 mm/yr. In between these two domains the Backbone Range is thrusted westward along the detachment connecting these two underplating windows, and experiences moderat