Seismic imaging revealing the processes from subduction to arc-continental collision in the northeastern South China Sea

Abstract

The northeastern margin of the South China Sea (SCS) is characterized by a tectonic shift from subduction in the south to arc-continent collision in the north. We describe the intraplate crustal-scale structure and deformation along a 256-km-long wide-angle reflection/refraction line perpendicular to the Manila Trench (MT). It is found that 1) the subducting plate of the northeast SCS comprises thinned continental crust with a thickness of 12–15 km and a high-velocity layer (HVL) with a thickness of 2–4 km, which is likely caused by (ultra)mafic intrusions; 2) the subducted upper crust is partly scraped off and accreted at the bottom of the accretionary wedge, and its characteristic low seismic-velocity may be due to subsequent hydration. Combined with previous investigations from six seismic lines in the study area across the MT and Southern Taiwan, from south to north, the velocity anomaly at the bottom of the accretionary wedge correspondingly undergoes a series of metamorphic processes in response to the transition from oceanic subduction to arc-continent collision.