Geotectonic Regionalization and Evolution of East China Sea and Northern South China Sea: ABSTRACT

Abstract

An analysis of geologic, geophysical, aeromagnetic, and drilling data suggests the marine basins on both sides of the fault along the western border of the East China Sea and the Beiwei-Shenhu fault in the South China Sea are different geotectonically, with respect to the nature of basement and the evolution of the Cenozoic sedimentary basins. Northwest of the faults, basement underlying these marine basins is formed of an extension to the Caledonian South China tectonic belt, where the Late Cretaceous to early Tertiary sedimentary basins is characterized by continental rifting. During the Neogene, the sedimentary basins evolved through continued bulk subsidence. In the shelf basin of the East China Sea, southeast of the faults, the Paleogene to lower Miocene sequence is characterized by geosynclinal sedimentation. During the Neogene to early Pleistocene orogeny, upper Miocene to Pilocene deposits were compressed into a series of bar-shaped folds, accompanied by reverse faulting. This series is apparently a marine northeastern extension of the Himalayan tectonic foldbelt west of the meridional valley of Taiwan. The tectonic foldbelt extends northeast to the Goshimg Islands in the southwest Sea of Japan, and Tsushima Island in the Korea Strait. Coastal mountains in eastern Taiwan are an independent tectonicmore » element adjacent to the western Pacific basin. Geologic and geophysical data suggest this tectonic element consists of remnant Neogene crustal fragments of oceanic type. The meridional valley in eastern Taiwan, which separates this element from the Himalayan Taiwan tectonic foldbelt of continental crust, is an A-shaped subduction belt, downthrust beneath the Pacific plate during the Neogene. This belt extends to the south, and may connect to the presently easterly downthrusting Manila Trench. The buoyancy of the continental crust in Taiwan is obstructing the process of subduction downthrusting in the north.« less