伸展盆地的结构形态及其主控动力学因素

Structural styles of extensional basins and their main controlling factors of dynamics

岩石圈伸展变形可以以不同方式发生,导致伸展盆地表现出不同特征的结构形态。根据盆地横剖面上的变形特征,伸展盆地的结构形态可以分为"拗陷""拗断""断陷"和"断拗"4种基本类型。岩石圈的伸展变形机制包括上地幔的热作用、岩石圈下部的韧性伸展和岩石圈上部(可能只是地壳浅层)的正断层作用。"拗陷"是地壳尺度的均匀伸展变形;而"拗断"和"断拗"都是地壳均匀挠曲变形和非均匀断裂变形叠加的产物。"拗断"和"断拗"这两种结构形态的伸展盆地的沉积充填部分是受伸展断层作用的影响,部分是伸展地壳挠曲变形的响应。虽然各种动力学因素同时存在,但是不同区域、不同时期各动力因素所占比例有所差异,导致伸展盆地在不同时期或同一时期不同区域的盆地结构形态有所差异。

The extensional deformation of lithosphere can occur by different patterns and results in different structures of extensional basins. According to the deformational characteristics on the cross-section of extensional basins, they can be divided into the following four types：＂ sag basin＂,＂ faulted-sag basin＂,＂ fauh-downthrown basin＂, and ＂sag fault-downthrown basin＂. The extensional deformation mechanisms of lithosphere include thermal action of the upper mantle, ductile extension of the lower lithosphere, and normal faulting of the upper lithosphere（ perhaps it is just shallow crust）. The ＂sag basin＂ is formed by homogeneous extensional deformation at crust scale; while the ＂fauh-downthrow basin＂ is shaped by faulting of nonhomogeneous extensional deformation at crust scale. Both ＂faulted-sag basin＂ and ＂sag fauh-downthrow basin＂ are the result of superposition of homogenous flexural deformation and non-homogeneous faulting deformation at crust scale, and their subsidence is controlled partly by extensional faulting and partly by flexural deformation of the extending crust. Although all of the mechanisms work simultaneously, the contribution of each dynamic mechanism varies in different parts of basin and at different periods, causing differences in extensional basin structures at different periods and in different parts of the basin at the same period.