Controls on Continental Strain Partitioning Above an Oblique Subduction Zone, Northern Andes
Controls on Continental Strain Partitioning Above an Oblique Subduction Zone, Northern Andes
复制标题
安第斯山脉北部斜俯冲带上方大陆应变分区的控制
作者：
J. Schütt;D. Whipp
在斜向会聚的板块边缘，应变分配到边缘平行的逆冲断层和走滑断层上是一个常见的过程，导致地壳薄片的形成和迁移。应变分配的程度和银迁移的速率可以与几个因素联系在一起，包括会聚角、俯冲倾角、板块之间的摩擦耦合和上板块的强度等。虽然这些因素是已知的是重要的，它们对应变分配的相对影响是不清楚的，特别是在自然边缘的因素往往会变化沿着走向。在这里，我们使用三维力学有限元模型来研究安第斯山脉（5°N-3°S）北方火山带（NVZ）的大陆地壳强度、会聚角、俯冲角和应变分配之间的关系。在NVZ的俯冲倾角和俯冲角都变化沿着走向，在大陆地壳的弱点可能存在于缝合带或弧火山活动的地区，应变分区只在某些地区观察到。因此，这是一个理想的位置，以了解其中的因素有最大的影响变形和条子形成的上板。我们的数值实验证实，一个适度高的结晶角是需要分区和大陆地壳的弱点，也需要一个连贯的大陆银的运动速度类似于从NVZ的大地测量观测。相反，俯冲倾角在控制应变分配行为方面只是次要的。
Strain partitioning onto margin‐parallel thrust and strike‐slip faults is a common process at obliquely convergent plate margins, leading to the formation and migration of crustal slivers. The degree of strain partitioning and rate of sliver migration can be linked to several factors including the angle of convergence obliquity, the dip angle of subduction, frictional coupling between the plates and the strength of the upper plate, among others. Although these factors are known to be important, their relative influence on strain partitioning is unclear, particularly at natural margins where the factors often vary along strike. Here we use a 3‐D mechanical finite‐element model to investigate the relationship between continental crustal strength, the convergence obliquity angle, the subduction angle, and strain partitioning in the Northern Volcanic Zone (NVZ) of the Andes (5°N–3°S). In the NVZ the subduction dip and obliquity angles both vary along strike, weaknesses in the continental crust may be present in suture zones or regions of arc volcanism, and strain partitioning is only observed in some regions. Thus, it is an ideal location to gain insight in which of the factors have the largest influence on deformation and sliver formation in the upper plate. Our numerical experiments confirm that a moderately high obliquity angle is needed for partitioning and that a continental crustal weakness is also required for movement of a coherent continental sliver at rates similar to geodetic observations from the NVZ. In contrast, the subduction dip angle is only of secondary importance in controlling strain partitioning behavior.