Kinematics of mountain-building in Taiwan
Abstract
Because of its high rates of convergence and erosion, the Taiwanese range is an ideal place to investigate the interactions between tectonics, erosion and climate. It has been viewed as a classical critical wedge essentially growing by frontal accretion of material. Such model of mountain-building is quite popular in numerical models that explore the interplay between tectonics and surface processes. However, in the case of Taiwan, we have recently shown that shortening across the wedge has been absorbed solely on the most frontal faults of the western foothills over the last ~2 Myr, which indicates that the range has grown by underplating rather than by frontal accretion. We propose here a new thermo-kinematic model of Taiwan that combines these findings as well as a wealth of new thermometric and thermochronological data on the long-term evolution of the orogen. All these data can be reconciled in a model in which exhumation has been essentially sustained by underplating. However, they also suggest that frontal accretion of rocks was dominant before ~1.5-2 Ma. Major changes in the kinematics of mountain-building therefore took place in the early Pleistocene. Whether these re-adjustments are related to climatic changes or to deeper processes is still an open question. Also, we derive long term erosion rates over the whole range from low-temperature thermochronology and from the thermal structures derived from the above kinematic scenarios. Our study thus sheds new light on the long-term evolution of the Taiwanese range and provides new geological quantitative constraints that need to be taken into account in future models exploring mountain-building processes and interactions between tectonics, erosion and climate.