依舒地堑汤原、方正断陷古近纪边界断裂活动特征

依舒地堑位于黑龙江省东部,为一新生代断陷盆地,汤原断陷和方正断陷为其两个面积较大的二级构造单元。通过对汤原断陷和方正断陷边界断裂的研究,可以进一步了解依舒断裂带的形成和演化过程。研究发现,在始新世-渐新世依舒地堑边界断裂的活动整体上具有多中心、不均衡的特征,汤原断陷东部的边界断裂为控盆断裂,方正断陷东、西两侧的边界断裂对盆地的发展都具有一定的控制作用,但西部边界断裂为主要控盆断裂。断层的生长指数分析表明,依舒地堑内部的北西向断裂与边界断裂的活动具有一致的规律性,都起到协调边界断裂演化发展的作用。依舒地堑边界断裂转换引张方向是由莫霍面梯度带的倾斜方向所决定,梯度带的倾向与地堑的整体伸展方向相同。

CHARACTERIZATION OF THE PALEOGENE BOUNDARY FAULTS OF TANGYUAN AND FANGZHENG FAULT BASINS IN YISHU GRABEN IN HEILONGJIANG PROVINCE

Lying in the east of Heilongjiang province, Yishu graben is a Cenozoic fault basin comprising two large second-class structural units, i.e., Tangyuan and Fangzheng fault basins. As a result, the structural study of the two units can help to find out the processes of formation and evolution of Yishu graben. Our results show that the activity of the boundary faults of Yishu graben is characterized by multiple centers and imbalance in Eocene-Oligocene epoch. The fault at the east boundary of Tangyuan fault basin is a basin-controlling fault, and the faults at both the east and the west boundaries of Fangzheng fault basin are also a basin-controlling fault, with the west boundary fault at Fangzheng being the major one. Analysis of the fault growth index shows that the NW fault within the graben is identical with the boundary fault in activity, and the two faults both serve to regulate the evolution and development of the boundary faults, and it was found that the transtension direction of the boundary faults of Yishu graben was determined by the Moho gradient tilt direction, since the latter is identical to the extension direction of the graben as a whole.