Slip re-orientation in oblique rifts

Abstract

Oblique extension is expected to result in a combination of dip-slip and strike-slip displacement along faults with strike orthogonal and oblique to the extension direction, respectively. This general concept is in disagreement with observations from natural oblique rifts, where faults show dip-slip kinematics indicating pure extension irrespective of the fault strike with respect to the regional extension direction. Consequently, along oblique structures, slip is re-oriented, and oblique to the applied extension direction. Besides, at fault scale, slip is re-oriented along strike such that it is dip slip at the fault center and becomes highly oblique slip toward the fault tips. Here, we use analogue experiments to show that this discrepancy can be resolved when a preexisting weak zone (WZ) is present in the crust at the onset of oblique extension. The WZ is implemented within the lower crust and strikes oblique to the extension direction. Our experimental results show that an inherited WZ within the ductile crust favors the re-orientation of slip such that oblique extension results in pure dip-slip displacement on faults that strike oblique with respect to the extension direction. Furthermore, we show that slip is re-oriented along strike of major faults, such that the fault center shows dip-slip kinematics, whereas its tips display strike-slip kinematics. These findings call into question the use of paleostress reconstructions to constrain plate kinematics in oblique extensional tectonic settings.