The geophysical interpretation of Yandang Low Uplift and discussion on its genesis in the East China Sea Shelf Basin

Based on the geophysical interpretation of seismic, gravity and magnetic data of the western East China Sea Shelf Basin, this paper studied the distribution configuration of Yandang Low Uplift in detail and concluded that the uplift lied between Oujiang Sag and Minjiang Sag in a discontinuous NE-trending, about 170 km long and 15 similar to 50 km in width. There are widespread Jurassic and Cretaceous strata on the Yandang Low Uplift covering about 5000 km(2) except some absence locally and the strata thickness is about 500 similar to 1500 m. Oujiang Sag distinctly differs from Minjiang Sag in the Mesozoic basin structure. The former is a typical faulted basin with "boundary fault in the east and overlap in the west" and well-developed faults. It also has well-developed Mesozoic half-grabens, tilted fault blocks. However, Minjiang Sag is a down-warped basin with less faults and igneous rock. Mesozoic compressional anticlines, faulted anticlines and inverted structures occur in large amounts. The uplift appears as a series of high value areas in NE-trending on free air gravity anomalies map and residual gravity anomalies map, while it appears as low magnetic anomaly areas in deep part on the Delta T magnetic anomalies map and there are high values of magnetic anomalies where igneous rocks exist. These geophysical features suggest that Yandang Low Uplift is a Proterozoic uplift which is different from Taipei low uplift. Meanwhile, this paper presumes that Yandang Low Uplift and Zhe-Min uplift may be joined in a single entity in Jurassic and divided into two parts in late Cretaceous according to the regional tectonic evolution and sedimentary characteristics.