GEOPHYSICAL FIELD AND DEEP STRUCTURES OF BAIYUN SAG, ZHUJIANG RIVER MOUTH BASIN

The Baiyun sag in the southern Zhujiang River Mouth Basin contains Cenozoic deep-water deposition system. This paper discusses the characteristics of gravitational and magnetic fields of the Baiyun sag and conducted a gravity-magnetic inversion along a long-cable seismic section across the sag. The negative area enclosed by +5mGal contour of the free-air gravity anomaly approximates the outline of the sag and corresponds to negative gravity and magnetic anomalies. The Moho surface shallows and the crust beneath the sag thins seawards stepwisely, indicating a transitional-type crust. Gravity modeling supports the proposal that there is a distinct Mesozoic subduction zone at the depth of the southern segment of the profile. The basement along the profile contains mainly acid-intermediate igneous rocks and secondarily metamorphic rocks and basic igneous rocks.