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

这个项目研究了冰岛西南部雷克雅尼斯半岛对倾斜扩展中心断层和断裂模式的控制：这是地球上少数几个倾斜扩展的大洋中脊变成地面的地方之一。该项目通过仔细研究断层和断裂模式记录的运动学历史，全面分析了斜向扩张中心的结构演化。该项目还考虑了对裂缝模式的理论力学控制，因此适用于世界范围内的斜向扩展中心。断层和裂缝的方向与它们的年龄和长度分布直接相关。此外，这些断裂所证明的应力和运动学历史在整个雷克扬尼斯半岛上都是空间上不同的，既是沿裂谷轴长度的距离的函数，也是与裂谷轴垂直距离的函数。这意味着，斜向扩张中心的断层和断裂形态及演化历史不能由扩张倾角的大小来决定。该项目正在检验这一假设，即应力场和断层/裂缝演化的时空变异性是由于板块扩展方向、沿裂谷轴线的活火山区域横向变化的岩浆压力以及沿裂谷边缘滑动的断层和地表单斜弯曲造成的局部应力扰动的综合影响。目前的项目正在通过对雷克雅尼斯半岛整个长度和宽度上断层和断裂方向的分布、演化史、运动学指标和解释的应力史的严格场分析来解决这些对斜向扩展中心应力场的控制。现场观测正在分析与火山活动中心的空间关系、喷发历史、地震行为和传播倾角。正在使用三维数值模型研究断层/断裂方向、断层运动学和区域应力历史中的空间变化的潜在力学控制，以处理与板块运动倾角、沿裂谷轴在空间和时间上变化的岩浆活动有关的构造特征，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.