半地堑盆地演化机制的粘弹塑数值模拟

MODELLING THE EVOLUTION OF A HALF GRABEN BASIN USING ELASTO-VISCOPLASTIC FINITE ELEMENT ANALYSIS

利用新近完成的粘弹塑构造模拟软件包对盆地的动力学演化进行了一系列模拟。文中主要概述不同厚度的上地壳中由高角度平面正断层界定的半地堑盆地的演化模拟。模拟时上地壳被考虑成具有Byerlee型强度包络 ,并且位于无粘性基底之上 ,盆地中由密度比地壳密度小的沉积物充填。计算了以一定增量逐渐拉伸上地壳层时各个阶段的非静岩应力 (Nonlitho staticstress)、塑性破裂 (Plasticfailure)分布及挠曲剖面 (Flexureprofile)。塑性变形使得有效弹性厚度减小。到切穿破裂出现以前 ,断层断距一直增加 ,之后 ,断距基本停止增加。所以 ,地壳强度使沉降量和隆升量均有极限。上地壳层厚度和沉积物密度是控制盆地宽度和极限深度的两个重要因素 ,上地壳层厚度增加或者沉积物密度加大都使盆地宽度和深度增大。模拟结果可以解释一些大陆裂谷盆地的宽度和沉积深度。

The evolution of a half graben basin bounded by normal faulting in the upper crust with a Byerlee type strength envelope has been modelled by elastoplastic finite element analysis. The substratum is assumed to be inviscid and the basin is filled by sediments lower in density than the crust. The nonlithostatic stresses, regions of failure and flexure profiles have been computed as the upper crustal layer is extended by progressive increments. The plastic deformation reduces the effective elastic thickness of the layer. The throw of the fault increases until thoroughgoing failure has become well established, after which the throw ceases to increase. Thus the strength of the layer limits the amount of subsidence and uplift that can occur. The thickness of the strong upper crustal layer and the density of the sedimentary infill are two important factors in controlling the width and maximum subsidence of the basins. Either increasing the layer thickness or increasing the density of the sedimentary infill has the effect on increasing the width and maximum subsidence of the basins. The most important application of the results is to interpret continental rift systems.