STRUCTURAL FEATURES OFF SOUTHWESTERN TAIWAN

Seismic reflection profiles reveal a complex system of faults, mud dia pirs, submarine channels, and sedimentary basins in the offshore area southwest of Taiwan. Structural patterns demonstrate the on-going stru ctural transformation from the passive Chinese continental margin to t he Taiwan collision orogen. The boundary between the Chinese continent al margin and the Taiwan orogen can be clearly delineated by the defor mation front of the contractional structures. West of the deformation front, ENE-WSW trending normal faults prevail in the continental margi n, which is characterized by a horst-and-graben structural style. East of the deformation front, west-vergent imbricated folds and thrusts s heets abound in the accretionary wedge. The structural grain of the ac cretionary wedge trends NNW-SSE in the deep offshore area but bends to ward NNE-SSW in the shallow near shore area. Mud diapirs emerge throug h thick sedimentary layers forming NNE-SSW trending anticlines that ex tend from near shore areas to onland Taiwan. Mud volcanoes have been o bserved on 3.5 kHz profiles over several diapirs. Structural styles ob served across the frontal portion of the submarine Taiwan accretionary wedge are strongly controlled by the tectonic evolution of the are-co ntinent collision. The structure and location of the deformation front are affected both by the growth of the accretionary wedge and by the geometry of the Chinese continental margin basement.