Deformation patterns of an accretionary wedge in the transition zone from subduction to collision offshore southwestern Taiwan

Abstract

Summary form only given. The area offshore southwestern Taiwan is the a place where the Luzon subduction complex first encroaches on the passive Chinese continental margin. Distinctive fold-and-thrust structures of the convergent zone and horst-and-graben structures of the passive margin are separated by a deformation front that extends NNW-ward from the eastern edge of Manila Trench and Penghu Canyon to the foot of the continental slope. Due to the outgrowth of the accretionary wedge as the influx of orogenic sediments increases toward Taiwan, the trend of the frontal folds and thrusts of the submarine accretionary wedge changes from a NNE-SSW direction near Luzon Island to a NW-SE direction north of 20 N. The NE-SW trending Chinese continental margin blocks the westward advance of the growing accretionary wedge, forces the NW-SE trending ramp anticlines gradually turning into a NNE-SSW trending direction across the continental slope and the Kaoping Shelf, then connects to the frontal thrusts of the mountain belt on land Taiwan. The Kaoping shelf and slope are frontal portions of the submarine incipient collision zone that are separated from the South China Sea shelf and slope by the Penghu submarine canyon. Presence of the complex Penghu submarine canyon system made exact location of the deformation front and nature of many morphotectonic features offshore SW Taiwan unclear.