Normal-fault development during two phases of non-coaxial extension: An experimental study

We use scaled experimental (analog) models to study the effect of a pre-existing fault fabric on fault development during extension. In our models, a homogeneous layer of wet clay undergoes two non-coaxial phases of extension whose directions differ by up to 45°. The normal faults that develop during the first phase create a pronounced fault fabric that influences normal-fault development during the second phase. In all models, the pre-existing faults are reactivated during the second phase of extension. Their sense of slip depends on the angle between the first- and second-phase extension directions. Specifically, the component of dip slip relative to strike slip decreases as the angle between the first- and second-phase extension directions increases. New normal faults also form during the second phase of extension in all models. The number of new fault segments increases as the angle between the first- and second-phase extension directions increases. The orientations of the new normal-fault segments are both orthogonal and oblique to the second-phase extension direction, indicating that both the second-phase extension direction and the pre-existing fault fabric control the orientation of new fault segments. Some of the new normal faults cut and offset the pre-existing faults, whereas others terminate against them, producing complex fault patterns and interactions. The modeling results explain fault interactions observed in the Jeanne d'Arc rift basin of offshore Newfoundland, Canada, and the reactivation of abyssal-hill normal faults at outer highs near subduction zones.