Fracture populations on the Reykjanes Peninsula, Iceland: Comparison with experimental clay models of oblique rifting

Abstract

We have used high‐resolution scanned air photos and field measurements to analyze fracture population systematics for the Reykjanes fissure swarm in order to determine the effect of rift obliquity on the evolution of fracture populations on the Reykjanes Peninsula, SW Iceland. The peninsula is oriented approximately 30° oblique to the direction of plate motion. Data show significant differences between the strike, length, and degree of development of fractures along the margin of the fissure swarm and those in the center of the zone of active volcanism. Along the margin, fractures are long, highly segmented extension fractures, and normal faults with offset on the order of several meters and a predominant strike 20° oblique to the trend of the plate boundary (rift axis). In the center of the zone of active volcanism, fractures are generally shorter, straighter, fewer in number, and strike approximately perpendicular to the direction of maximum horizontal extension and parallel to the trend of eruptive fissures. Right‐lateral oblique‐slip faults striking approximately perpendicular to the spreading direction are present in the center of the rift zone. Scaled experimental models of oblique extension predict a significant change in fracture strike at the rift margins due to the presence of a secondary stress field; on the Reykjanes Peninsula, this corresponds to the boundary between thicker and thinner brittle crust. The models confirm that right‐lateral oblique‐ or strike‐slip faults accommodate significant left‐lateral shear where deformation is distributed in a rift zone.