Evolution of E-W strike-slip fault networks, the northwestern foreland of Tunisia

The northwestern foreland of Tunisia (El Kef region and its surroundings) is a key area to study the tectonics of main E-W basement strike-slip faults and related structures. To achieve this goal, we used multidisciplinary approaches including field work, paleo-stress analyses and geophysical data. These approaches allowed us to propose a new structural model based on the evolution in space and time of Riedel shear type faults and to highlight their role in the structuring of the study region. During the Mesozoic, E-W normal oblique-slip basement faults (D1: Ghardimaou fault, D2: El Kef-Ouergha fault, D3: Jebel Harraba-Guern Halfaya fault and D4: Tajerouine fault) controlled the architecture and the subsidence of the El Kef Basin within a transtensive setting by block tilting, NE-SW negative flower structures, Triassic salt ascent and deposits thicknesses and facies variations. During the Eocene and Late Miocene, the NW-SE shortening (tectonic inversion) is expressed by the oblique reactivation of the pre-existing E-W faults as dextral strike-slip faults. This reactivation is accompanied by map-scale Riedel shear type faults, where D1, D2, D3 and D4 formed the principal displacement zones (PDZs). The successive movements of these faults cut the study area in several right-lateral shear bands in which subsidiary Riedel fractures (R, R', X, P, T and Y) and NE-SW folds are developed. Fault slip data and fractures analyses, across the study area, show several fracture systems which interact under a NW-SE SHmax. During Quaternary, the NNW-SSE shortening reactivated the preexisting E-W fault networks (PDZs). It also, formed NS left-lateral strike-slip faults, NW-SE grabens, NE-SW reverse faults, and ENE en echelon folds arranged within Riedel shear bands.