Pre-rift Denudation, Large Scales of Basalt Eruption and Multidirectional Extension in the Jianghan Basin, Central China: An Active Rift Model

The Jianghan basin is an intracontinental rift basin lying in the Middle of Yangtze Block, central China, with a total area of 28, 000 Km2. The basin is located on the North-South Gravity Lineament (NSGL) of the eastern China. Using drilling data, 2-D and 3-D seismic reflection data and field outcrop, we try to explain the dynamic processes of the Jianghan Basin. The Cretaceous tectonic evolution of Yangtze Block was characterized by widespread extensional basins. The Jianghan basin was formed under this background and began intensively rifting during Late Cretaceous, depositing more than 3000 m thick stratum. The lower Cretaceous was a series of depression sequences and locally deposited on the basin margin. While they are absent in the other part of the basin which experienced intensively rifting during the Late Cretaceous to Paleogene. We tentatively contribute this to the thermal uplift before syn-rift stage. Basalts in this study were identified through drilling data and seismic data, which erupted throughout the syn-rift stage. The largest scale of basalt erupted during the Middle Eocene. The area, average frequency and thickness of the basalts during this stage are 7, 282 Km2, 10 times and 85 m, respectively. The Jianghan Basin experienced three-stage rifting during the syn-rift stage (the Late Cretaceous to Paleogene). 4 sets of faults (NW-SE, NNE-SSW, NE-SW and nearly EW-striking) were active during Rift Phase 1. During Rift Phase 2 and 3, NW-SE-striking faults almost ceased, while a new set of NE-SW-striking faults grew. Although these faults were mainly reversed by pre-existing faults, their multidirectional strikes indicated that there was no unified regional extensional direction. Pre-rift denudation, large scales of basalt eruption and multidirectional extension in the Jianghan Basin can be explained by an active rift model. In this model, the lithosphere was warming up by rising diapric plumes of hot mantle, resulting in the absence of lower Cretaceous within the basin. The active hot mantle upwelling induced lithosphere extension and reactivated the pre-existing faults, forming the complex fault networks. The upwelling of mantle and eruption of basalts may be a result of the partially melt of the flowing asthenosphere from west to east, across the NSGL.