THE DEEP FAULTS SEPARATING LAND AND SEA BASINS IN LOWER YANGTZE REGION AND THEIR TECTONIC SIGNIFICANCE

The Subei Basin, land part of the Lower Yangtze region, has significant difference in the morphology, properties and distribution pattern of crystalline bedrocks with the South Yellow Sea Basin, offshore part of the Lower Yangtze Region. On the Indo-China-surface geological map, the NEE tectonic lines consisting of narrow strips support the assumption of asymmetric ramp tectonic movement, while in the offshore side, the tectonic lines are dominated by those in nearly EW direction. According to the traditional point of view, the central uplift of the South Yellow Sea Basin, where the magnetic anomalies of the lower Yangtze region is well developed, is equivalent to the magnetic anomaly bodies of the Sichuan and the Jianghan Basins on the upper and middle Yangtze respectively. 2D seismic data has revealed a thick sequence of Pre-Mesozoic deposits which is more than 5,000 meters thick, indicating that the central uplifting area of the traditional Lower Yangtze region was a huge depression before Mesozoic and the offshore part of the South Yellow Sea Basin which is similar with the upper and middle Yangtze Regions. However, owing to the seismic blank in the coastal shallow water, the comparative study of the land and sea part basins faces difficulties. Based on gravity and high precision aeromagnetic data, the authors discovered a NW-trending deep fault-the Chenjiagang fault zone between the coastal Jiangsu and South Yellow Sea, and for the first time confirmed that the land and sea parts of the South Yellow Sea Basin was tectonically faulted. As the results, both stratigraphy, depositional and tectonic characteristics on the two sides of the fault are different.