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四川省西昌地区中更新统昔格达组地层的变形变位等资料表明,该区的应力图象具有明显的分区性。即大致以礼州为分界,北部泸沽、冕宁一带以强烈的褶皱变形为主,推测其主压应力方向为北西西;而礼州以南的西昌、邛海附近则广泛发育张性正断层,表明是一引张区。如何从这些局部的构造变形遗迹反演区域应力场,并较好地解释在一小范围内挤压和引张共存的特殊现象,是我们的目的。本文从地质体介质力学性质差异是影响局部应力状态的主要因素这一思想出发,提出了刚性块体接触关系的“边边—点边”演化模式,能较好地解释上述现象。最后,用平面有限元方法模拟了西昌地区的应力场,计算结果与实际资料吻合。“边边——点边”块体接触关系的演化模式,对于解释西南地区一系列串珠状窄长盆地和断陷谷的成因具有一定的启发性意义。
The deformation and deformation of the Xigeda Formation in the Middle Pleistocene in Xichang, Sichuan Province indicate that the stress image in this area has obvious zoning characteristics. That is, roughly Liyizhou as the boundary, the north of Lugu, Mianning area with strong fold deformation, presumably the direction of the principal compressive stress of the North West; and south of Liuxi Xichang, near the sea is widely developed Changxing fault, that Is a lead Zhang area. How to retrieve the regional stress field from these local tectonic deformations and explain the special phenomena of coexistence of extrusion and tension in a small area is our goal. Based on the idea that the difference of mechanical properties of geologic bodies is the main factor affecting the local stress state, this paper puts forward the “edge-point-edge” evolutionary mode of contact of rigid blocks, which can well explain the above phenomenon. Finally, the finite element method is used to simulate the stress field in Xichang region. The calculated results are consistent with the actual data. The evolutionary pattern of “edge-point-edge” block contact is of some enlightening significance for explaining the causes of a series of beaded narrow-shaped basins and fault-depression valleys in the southwestern region.