Tectonic Versus Magmatic Controls on Stress Field Characteristics, Fracture Patterns, and Fault Evolution at an Oblique Spreading Center

本项目研究了冰岛西南部雷克雅内斯半岛斜向扩张中心断层和断裂模式的控制因素：地球上少数几个由斜向扩张的洋中脊变为陆上的地方之一。该项目涉及通过仔细检查断层和断裂模式记录的运动学历史，全面分析斜向扩张中心的构造演化。该项目还考虑了断裂模式的理论力学控制，因此适用于全世界的斜向扩张中心，断层和断裂的方向与它们的年龄和长度分布直接相关。此外，应力和运动学的历史证明，这些裂缝是空间可变的整个雷克雅未克半岛，无论是作为一个函数的距离沿着长度的裂谷轴，并作为一个函数的距离垂直离开它，这意味着扩张的角度不可能是唯一的控制故障和断裂模式和演化历史在一个斜向扩张中心。该项目正在检验这样一种假设，即应力场和断层/断裂演变的空间和时间变化是由于板块扩张方向、活火山活动区沿着裂谷轴的横向可变岩浆压力、和局部应力扰动所造成的滑动断层和表面单斜弯曲沿着裂谷边缘。目前的项目是解决这些控制斜向扩张通过对断层和断裂方向的分布、演化历史、运动学指标以及Reykjanes半岛长度和宽度上的应力历史进行严格的现场分析，确定中心应力场。现场观察正在分析的背景下，空间关系的火山活动中心，喷发历史，地震行为，和蔓延的同源性。正在使用3-D数值模型来检查断层/裂缝方向、断层运动学和区域应力历史空间变化的潜在机械控制，以解决与板块运动倾角、沿着裂谷轴的空间和时间变化的岩浆活动相关的结构特征，以及现有活动构造对局部应力模式的影响。

This project examines the controls on oblique spreading center fault and fracture patterns on the Reykjanes Peninsula in southwest Iceland: one of the few places on Earth where an obliquely-spreading mid-ocean ridge becomes subaerial. The project involves a comprehensive analysis of the structural evolution of an oblique spreading center through close examination of the kinematic history recorded by fault and fracture patterns. The project is also considering theoretical mechanical controls on fracture patterns and is thus applicable to oblique spreading centers worldwide.Orientations of faults and fractures are directly linked to their ages and length distributions. Furthermore, the stress and kinematic histories evidenced by these fractures are spatially variable across the Reykjanes Peninsula, both as a function of distance along the length of the rift axis and as a function of distance perpendicularly away from it. This implies that the angle of spreading obliquity cannot be the sole control on fault and fracture patterns and evolutionary history at an oblique spreading center. The project is testing the hypothesis that spatial and temporal variability in stress fields and fault/fracture evolution is due to the combined influence of the plate spreading direction, laterally variable magma pressures in the zone of the active volcanism along the rift axis, and local stress perturbations caused by slipping faults and surface monoclinal flexures along the rift margins.The current project is addressing these controls on oblique spreading center stress fields through a rigorous field analysis of the distribution of fault and fracture orientations, evolutionary history, kinematic indicators, and interpreted stress history across the length and width of the Reykjanes Peninsula. Field observations are being analyzed in the context of spatial relationship to centers of volcanic activity, eruptive history, seismic behavior, and spreading obliquity. Underlying mechanical controls on spatial variations in fault/fracture orientations, fault kinematics, and regional stress history are being examined using 3-D numerical models to address structural characteristics in relation to plate motion obliquity, spatially and temporally variable magmatic activity along the rift axis, and the impact of existing active structures on local stress patterns.