Tectonic erosion and the removal of forearc lithosphere during arc-continent collision: Evidence from recent earthquake sequences and tomography results in eastern Taiwan

Abstract

A very common but important observation of collided and accreted volcanic arcs is that the forearc regions of these arcs are largely or even entirely missing. The processes and mechanisms responsible for the removal and transport of the forearc materials from the collisional belts are thus important issues in understanding tectonics and crustal growth. The young and ongoing collision between the Luzon volcanic arc and the Eurasian continental margin that forms the island of Taiwan provides a rare opportunity to examine these processes and mechanisms as they occur. From observations of a new detailed 3-D tomography combined with relocated hypocenters of two earthquake sequences occurred in 2003 and 2006, we found that the Luzon forearc lithosphere initially underthrusts westward after the collision began. As the collision proceeds, the forearc basement then subducts eastward beneath the colliding and accreting Luzon arc along a major fault system in eastern Taiwan. Thus the Luzon forearc lithosphere appears to be removed by tectonic erosion and is being transported eastward into the mantle. Our results from the active Taiwan orogen will provide important insights for interpreting rock records from many old arc-continent collisional belts in the world.