Deformation styles related to intraplate strike-slip fault systems of the Saharan-Tunisian Southern Atlas (North Africa): New kinematic models

Abstract

The complex geometry and tectonic evolution of the Saharan-Tunisian Southern Atlas strike-slip fault systems, North Africa, have not been investigated comprehensively to date. This paper proposes new conceptual models to better understand the structural styles along these intraplate fault zones. We use a multidisciplinary approach including field observations, geological mapping, stress analysis and seismic data to investigate the development and interaction of major strike-slip fault segments. The regional fault system is dominated by the E-W trending Biskra, Alima, Orbata, Bouhedma and Chotts basement faults that constitute the Principal Displacement Zones (PDZs).Our analyses and interpretations reveal that each PDZ has a typical dextral strike-slip architecture comprising multi-scale fault segments that are linked through dilational and contractional stepovers/bends. During Mesozoic times, under NE-SW Shmin, the transtensional fault segments of Biskra and Alima formed the boundaries of the Khanguet Sidi Neji-Gafsa (KSG) Basin, which developed as a Z-shaped dextral releasing stepover. During the Cenozoic, the KSG Basin was inverted, under NW-SE SHmax, in response to the Africa-Eurasia convergence. This inversion occurred mainly along basin sidewalls by reactivation of the pre-existing normal-oblique faults as right-lateral transpressional shears. Further east, the E-W dextral strike-slip faults of Orbata and Bouhedma connected via a NE-SW restraining stepover.Finally, all E-W dextral strike-slip fault segments are associated with ENE right-stepping en echelon folds and Riedel shear patterns of different scales, in response to basement wrenching. Currently, most fault zones are still active with deep strike-slip earthquakes.