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

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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.