Arc-continent collision in Taiwan: New marine observations and tectonic evolution

Abstract

Marine observations offshore of Taiwan indicate intense deformation of the Luzon arc-forearc complex, with episodic eastward migration of the active deformation front across the complex. This active tectonic domain absorbs a significant amount of shortening between the Eurasia margin and the Philippine Sea plate, which is moving toward N310°E at about 8 cm/yr relative to Eurasia. Swath bathymetry and backscattering data, together with seismic reflection and geopotential data obtained during the ACT (Active Collision in Taiwan) cruise onboard the R/V L'Atalante, showed major north to south changes in the tectonic style in both the indenting arc and the host margin. Structural observations show that the forearc basement of the Luzon arc no longer exists north of 22°30′N. To the south, only a small part of the forearc domain may remain beneath the Huatung Ridge (rear portion of the former Manila Trench oceanic accretionary wedge including forearc and intra-arc sequences) and rear of the thrust wedge. A tectonic model involving the progressive underthrusting of large slices of the forearc basement may account for the contrasting styles of deformation encountered from south to north across the collisional orogen and apparent nonexistence of the forearc region. The progressive subduction of the continental margin of China induces: (1) to the south, major eastward backthrusting and shortening of the forearc domain between the former oceanic accretionary wedge and the Luzon arc volcanic edifice, (2) to the north, accretion of parts of the arc domain to the collisional belt associated with westward thrusting, eastward backthrusting at the base of the slope and block rotation.