伸展构造离散元数值模拟-以琼东南盆地为例

Discrete Element Numerical Simulation of Extensional Tectonics-Examples of Qiongdongnan Basin

现今琼东南盆地大地热流在空间上显示出一定的热流分布规律,盆地东部低热流区域基底偏刚性,而盆地高热流区域基底偏韧性.考虑基底性质(刚性和韧性)对琼东南盆地断裂组合发育的影响,开展了两组数值模拟.模拟结果显示,刚性基底的上覆地层呈铲状半地堑构造,发育不对称的单侧台阶状地堑,断陷一侧为缓坡,另一侧边界发育有坡度较大的正断层,断层数量较少,单一断层的断距较小;而韧性基底的上覆地层凹陷凸起间隔分布,凹陷内多发于次级断层,断层数量多,单一断层的断距较小.位于凹陷内部发育的2级和3级断层倾向还受到基底刚、韧性的影响,刚性基底上部凹陷内主要发育与伸展应力相同倾向的正倾向断层,韧性基底上部则发育多组倾向相反的断层.

The present terrestrial heat flow in Qiongdongnan Basin shows a certain distribution law of heat flow in space.The basement of the low-heat flow region in the eastern part of the basin is rigid,while the basement of the high-heat flow region in the basin is toughness.In this paper,considering the influence of basement lithology(rigidity and toughness)on the development of fault assemblage in Qiongdongnan Basin,two sets of numerical simulations are carried out:.The simulation results show that the overlying strata of the rigid basement is a listric half-graben structure,with asymmetrical one-side step-like graben.One side of the fault depression is a gentle slope,and the boundary of the other side is a normal fault with a large slope.However,the depressions and bulges of the toughness basement are spaced,and secondary faults is often found in the depressions,with a large number of faults and a small fault interval for a single fault.The secondary and tertiary faults in the depressions are also affected by the stiffness and toughness of the basement.In the depressions of the upper part of the rigid basement,there are mainly positive dip faults with the same tendency as the extensional stress,while in the upper part of the toughness basement,there are several groups of faults with the opposite tendency.