ON THE EVOLUTION OF THE RYUKYU ARC AND THE BASIN OF THE EAST CHINA SEA

Abstract

The East China Sea is commonly used by gcoscientists to refer to west of the sea area of the Ryukyu Island Arc, including the Okinawa Trough and the Continental Shelf of China. The former is a secondary sea basin of tensile in nature, and the latter is a marginal sea basin originating from the block faulting of the frontal border of the China continent proper. Since the beginning of the present century the above area has attracted wide interests of many geoscientists. Geophysical and geological samplings and deep sea dredgings conducted In the said area have provided much of the desired data. In this article, the authors deal mainly with the genesis and evolution of the Ryukyu Arc and the East China Sea including the tectonic classification of the sea area. The study encom- passes the preliminary analysis of gravity profiles and magnetic and bathymetric measurements along the navigation line beginning from the west border of the continental shelf in the East China Sea. through the Okinawa Trough, the Ryukyu Arc and the Ryukyu Trench,to the Daito Islands. The classification of the tectonic units of the East China Sea and discussion on the deep-seated structure of the area from the East China Sea Basin to the Okinawa Trough have been made on the basis of the variations of the gravity, magnetic fields,the acoustic profile, heat flow units of the sea bottom. as well as the geological, topographic and stratigrghic features of the west border of the East China Sea. Finally, the authors present and evolution- ary model for the origin of the East China Eea.