Rift-Parallel Strike-Slip Faulting Near the Iceland Plate Boundary Zone: Implications for Propagating Rifts

Strongly lineated terrain outside of Iceland's active plate boundary zones is created by faults and dikes aligned with the rift zones where they formed, similar to the spreading fabric defined by abyssal hills generated at mid-ocean ridge spreading centers. As expected, rift-parallel normal faults and fissures dominate in the active rift zones, but in older crust to the east and west, faults with strike-slip and oblique-slip displacements dominate. Some areas have widespread, small-scale, strike-slip, and oblique-slip faults, while others have more widely spaced, larger, strike-slip fault zones. In most cases, the strike-slip and oblique-slip faults strike subparallel to nearby older dikes and normal faults assumed to indicate the orientation of the rift zones where they formed. Strike-slip displacements overprinting normal faults and along dike margins suggest reactivation of spreading-related zones of weakness. More complicated fault geometries and kinematics occur near the oblique rifts and the major transform fault zones. The sense of movement on the strike-slip and oblique-slip faults is broadly systematic with respect to the active Northern and Eastern Rift Zones supporting the interpretation that they are the result of crustal block rotations on either side of rift zones that propagate to the north and south away from the center of the Iceland hot spot. Similar fault kinematics may occur along mid-ocean ridges and other magmatic rifts where rift propagation occurs on a range of scales.