Variable coupling across weak oceanic transform fault: Flateyjarskagi, Iceland

Abstract

Tectonic studies near major fault zones often reveal multiple tectonic regimes. Do these regimes indicate multiphase tectonism with distinct episodes, or do they reflect single-phase tectonism with time-space perturbations along lithospheric weakness zones? Based on tectonic analyses in Flateyjarskagi, North Iceland, we reconstruct the late Cenozoic tectonic regimes related to right-lateral transform motion along the Tjornes Fracture Zone, which connects the Kolbeinsey Ridge and the North Iceland Rift. Rifting and transform motion have induced eight normal and strike-slip regimes, four of which are inconsistent with the overall kinematics (as a probable result of stress drop, elastic rebound and dyke injection). For the consistent regimes, contrasting angles between extension and transform trends reflect repeated changes from moderate (25°) to very low mechanical coupling (85°) across the transform zone. Thus, the tectonic regimes need not be interpreted in terms of numerous tectonic episodes but rather as a consequence of variable coupling across the transform zone.