The evolution of crustal deformation in an oceanic extensional environment

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Fault statistics collected along the slow-spreading Reykjanes Ridge are used to investigate its complex tectonic evolution. The Reykjanes Ridge is oriented oblique to the spreading direction and is located close to the Iceland hotspot. A wide distribution in fault strike and fault throw occurs across the axis of the Reykjanes Ridge, with a sharp change 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 distribution 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 controlled by the plate tectonic generated regional stress field. Outside the axial zone the faults strike oblique to the spreading normal direction. This change in fault strike, coupled with the lack of any evidence for strike-slip movement, suggests that these faults develop as a passive response to the thermal evolution of the lithosphere. Our results indicate that at a slow-spreading ridge the crust is deformed by two stress fields, one responsible for the fault formation within the axial zone, the other for the faults which bound the axial zone.