Kinematic evolution of a large-offset continental normal fault system, South Virgin Mountains, Nevada
Kinematic evolution of a large-offset continental normal fault system, South Virgin Mountains, Nevada
复制标题
内华达州南维尔京山脉大偏移大陆正断层系统的运动演化
DOI：
--
复制
发表时间：
2000
期刊：
影响因子：
--
通讯作者：
J. Fryxell
中科院分区：
文献类型：
--
作者：
R. Brady;B. Wernicke;J. Fryxell
南维尔京山脉和大瓦什海槽构成了一个中中新世正断层系统，该系统界定了东部未伸展的科罗拉多高原和西部中央盆地和山脉省高度伸展的地壳之间的边界。在地壳上部3公里处，该系统发育在科迪勒褶皱冲断系前陆的次水平克拉通地层中。该地区崎岖的地形和缺乏植被提供了特殊的三维曝光。岩石的致密地层学和明确的前断层构造使系统得以详细重建。根据300km2的1：12 000比例尺详图重建的剖面表明，该断裂系统容纳了15多公里的大致东西向的中新世伸展。伸展作用最初适应于中倾角至陡倾角的里氏正断层。随着早期断层和断块的倾斜，在断块内部启动了陡峭至中等倾角的断层，最终形成早期断层。一些早期断裂在倾角20°时活动。由于断块的活动滑动和多米诺骨牌式的旋转，均衡驱动的倾斜作用叠加在倾斜作用上。总体而言，这些过程将原本陡峭的断层旋转到水平方向。运动学与普遍接受的观点不一致，即许多近水平的正断层被后来的横切正断层旋转到现在的方向。然而，对其他地区的重新审查表明，在南维尔京山脉看到的进化序列实际上可能广泛适用。
The South Virgin Mountains and Grand Wash trough comprise a mid-Miocene normal fault system that defines the boundary between the unextended Colorado Plateau to the east and highly extended crust of the central Basin and Range province to the west. In the upper 3 km of the crust, the system developed in subhorizontal cratonic strata in the foreland of the Cordilleran fold and thrust system. The rugged topography and lack of vegetation of the area afford exceptional three-dimensional exposures. Compact stratigraphy and well-defined prefaulting configuration of the rocks permitted a detailed reconstruction of the system. Reconstruction of cross sections based on more than 300 km2 of detailed mapping at a scale of 1:12 000 shows that the fault system accommodated more than 15 km of roughly east-west–directed Miocene extension. Extension was initially accommodated on moderately to steeply dipping listric normal faults. As the early faults and fault blocks tilted, steeply to moderately dipping faults initiated within the fault blocks, soling into the early faults. Some of the early faults were active at dips of <20°. Isostatically driven tilting is superimposed on tilting due to active slip and domino-style rotation of the fault blocks. Collectively these processes rotated originally steeply dipping faults to horizontal orientations. The kinematics are inconsistent with the widely accepted view that many near-horizontal normal faults were rotated to their present orientations by later, crosscutting normal faults. However, reexamination of other areas suggests that the evolutionary sequence seen in the South Virgin Mountains may, in fact, be widely applicable.