THE EVOLUTION OF CRUSTAL DEFORMATION IN AN OCEANIC EXTENSIONAL ENVIRONMENT

Fault statistics collected along the slow-spreading Reykjanes Ridge ar e used to investigate its complex tectonic evolution. The Reykjanes Ri dge is oriented oblique to the spreading direction and is located clos e to the Iceland hotspot. A wide distribution in fault strike and faul t throw occurs across the axis of the Reykjanes Ridge, with a sharp ch ange in mean strike and mean throw occurring at the edge of the axial zone. Within the axial zone there is no significant change in the dist ribution of faults with increasing distance from Iceland; proximity to the hotspot does not influence the detailed tectonics near the axis. We infer that the fault development within the axial zone is controlle d by the plate tectonic generated regional stress field. Outside the a xial zone the faults strike oblique to the spreading normal direction. This change in fault strike, coupled with the lack of any evidence fo r strike-slip movement, suggests that these faults develop as a passiv e response to the thermal evolution of the lithosphere. Our results in dicate that at a slow-spreading ridge the crust is deformed by two str ess fields, one responsible for the fault formation within the axial z one, the other for the faults which bound the axial zone.