Slip re-orientation in oblique rifts

Abstract

Oblique extension is expected to result in a combination of dipslipand strike-slip displacement along faults with strike orthogonaland oblique to the extension direction, respectively. This general conceptis in disagreement with observations from natural oblique rifts,where faults show dip-slip kinematics indicating pure extension irrespectiveof the fault strike with respect to the regional extension direction.Consequently, along oblique structures, slip is re-oriented, andoblique to the applied extension direction. Besides, at fault scale, slipis re-oriented along strike such that it is dip slip at the fault center andbecomes highly oblique slip toward the fault tips. Here, we use analogueexperiments to show that this discrepancy can be resolved whena preexisting weak zone (WZ) is present in the crust at the onset ofoblique extension. The WZ is implemented within the lower crust andstrikes oblique to the extension direction. Our experimental resultsshow that an inherited WZ within the ductile crust favors the re-orientationof slip such that oblique extension results in pure dip-slip displacementon faults that strike oblique with respect to the extensiondirection. Furthermore, we show that slip is re-oriented along strikeof major faults, such that the fault center shows dip-slip kinematics,whereas its tips display strike-slip kinematics. These findings call intoquestion the use of paleostress reconstructions to constrain plate kinematicsin oblique extensional tectonic settings.