分层伸展叠加变形二维离散元模拟

Superimposed Extensional Deformation of Different Layers: Insights from Two Dimensional Discrete Element Modeling

分层伸展叠加变形是裂陷盆地演化过程中普遍存在的一种复杂的构造地质现象,是裂陷盆地构造地质研究和油气成藏研究的热点。目前有关分层伸展叠加变形的研究仍处于几何学描述阶段,缺乏对其动力学演化过程的解析。本文采用构造地质研究领域中新兴的模拟方法——离散元,通过构建离散元模型模拟研究分层伸展叠加变形的断裂发育过程。结果表明:(1)上下两套伸展断裂系统之间是否存在韧性滑脱层(泥岩层或膏岩层)是分层叠加变形的主控物质因素;(2)中间韧性地层隔断了下部断层向上的继承性发育,从而形成上下两套断裂系统分层伸展,垂向上叠加的变形特征;(3)受韧性地层侧向牵引作用影响,上部断裂系统的横向展布明显扩大;(4)在相同岩性条件下,降低伸展速度会显著降低两侧断层发育的差异性,但不会改变垂向上分层伸展的变形特征。研究解析了分层伸展叠加变形的动力学演化过程,有助于进一步认识分层伸展叠加变形机制及其对油气运聚成藏的控制作用。

Superimposed extensional deformation of different layers is a complex tectonic deformation in the evolution of rift basins.Many researches have been carried out on superimposed extensional deformation,most of which are focused on geometry description.Few investigations have been carried out on the dynamic evolution of superimposed extensional deformation.The main objective of this study is to simulate the evolution of the fault system in superimposed extensional deformation of different layers using discrete element modeling.Modelling results showed that the presence of ductile strata embedded in the middle part of the model has a significant influence on superimposed extensional deformation of different layers.Moreover,the results also demonstrate that the ductile strata embedded in the model,separating the upper and lower brittle strata,resulted in two fault systems.The upper fault system is far wider than the lower fault system,due to lateral extension of the middle ductile strata.Decreasing extensional velocity decreases the difference of development of fault system between the upper and the lower brittle strata,but does not affect superimposed extensional deformation.Our numerical models are consistent with seismic profiles of the Nanpu Sag.This study provides basic insight into the dynamic evolution of the superimposed extensional deformation of different layers.