Gravity and magnetic field and tectonic structure character in the southern Yellow Sea

摘要

The research of the geophysical survey in the east of the southern Yellow Sea (SYS) (122° — 125°E) in 1999 reveals that the SYS has a structure of three-uplifts and two-basins. The structure can be well concordant with the gravity and magnetic anomalies. In the basins, most of the gravity and magnetic anomalies are low and gentle. As well in the uplifts, the gravity anomalies are high positive ones, but the magnetic anomalies are plus and minus variant ones. Seismic data show that the mid-uplift is a Cenozoic one. The Paleozoic is under the Q+N strata, the thickness of which is less than 1 km, with no Palaeogene. The Wunansha uplift area and the Sunan uplift area have good continuity, which indicates that they belong to the same geological unit. The basin in the northern part of SYS, which developed in the late Cretaceous period, is a Cenozoic one mainly made up of Cenozoic sediment. On the contrary, the basin in the southern part is the seaward extension of Subei basin and is a medial Cenozoic sediment basin mainly made up of Cenozoic sediment. Because of the striking left-lateral sense translation of Tanlu fault zone, the east plate of fault zone moved northward on a large scale, which generated a massive north-south pull-apart stress field to make the earth crust pulled apart, revolved and tilted, and the pu11ing-apart basin came into being in the upper part of the crust.