Inversion of transfer faults: The Jebha–Chrafate fault (Rif, Morocco)

Abstract

Wrench faults include both conjugate strike-slip faults and transfer or tear faults, which have different attitudes with respect to regional stresses and structures. The kinematic and paleostress field analysis of these fault zones are key observations to reveal their evolution and analyze reactivation and inversion processes. The Jebha–Chrafate fault is an ENE–WSW major transfer fault of the Rif Cordillera, formed during the southwestwards displacement of the Internal Zone on the Flysch units and the External Zones. Analysis of minor structures along the Jebha area indicates top to the SW motion of low and high-angle normal faults that is responsible for crustal thinning and the development of the Alboran Basin, during the last stages of Rif tectonic wedge emplacement. In addition, most of the kinematic indicators along the Jebha–Chrafate fault point to an initial sinistral regime. However, small scale structure analysis evidences a reactivation and inversion of the fault zone as dextral during the recent Eurasia–Africa plate convergence, with a final overprinting of normal faults during the late stages of relief uplift. Despite its length and its sharp mountain front, the Jebha–Chrafate fault is inactive because it does not affect Plio-Quaternary deposits; it moreover entails a low seismic hazard. The Jebha–Jebha–Chrafate fault illustrates the complex evolution of transfer faults that start to develop in the initial stages of tectonic wedge development, with main shear stresses parallel to the fault surfaces, followed by oblique stresses that determine its inversion and reactivation with opposite slips.