Recent spatial and temporal changes in the stress regime along the southern Tunisian Atlas front and the Gulf of Gabes: New insights from fault kinematics analysis and seismic profiles

Abstract

Tectonic deformations in the Southern Atlassic Front of Tunisia (SAFT) and the Gulf of Gabes result from the Nubia-Eurasia convergence. This study, based on the inversion of geologically determined fault slip vectors, presents evidences for spatial and temporal changes in the stress state. Fault kinematics analyses reveal a temporal change in states of stress during the late Cenozoic. A paleostress (Miocene-Pliocene) state is characterized by a regional compressional tectonic regime with a mean N134±09°E trending horizontal maximum stress axis (σ 1 ). A modern (Quaternary to present-day) state of stress also corresponds to compressional tectonic regime with a regionally mean N05±10°E trending horizontal σ 1 . The SAFT corresponds to two distinct domains: a far-foreland Atlassic front related to contractional deformation associated with southward propagate thrusting, and eastward, the Gulf of Gabes characterized by normal component NW to WNW trending faults at the crustal margin scale probably related with a transtensional tectonic regime. We propose that the spatial and temporal changes in the stress during the Miocene-Pliocene and Quaternary may result from the geodynamic evolution of the Tunisian Atlas in relation to the rotation of Corsica-Sardinia blocks and the separation of the Sicilian continental lithosphere from the Ionian oceanic lithosphere.These temporal and spatial stress changes along the SAFT and the Gulf of Gabes are probably the engine behind the moderate seismicity, leading at the same time to a reactivation of the inherited major structures created during the evolution of the Southern Tethyan margin.

Style of Atlassic tectonic deformation and geodynamic evolution of the southern Tethyan margin, Tunisia

“…The restoration of the cross section shows that the Orbata thrust system consists in inherited half-grabens system with N-dipping faults allowing the northward thickness increase of the Mesozoic series (Fig. 12) reported previously (Gharbi et al, 2013(Gharbi et al, , 2014. Field data and the restoration of the cross section suggest that the Orbata anticline results from the inversion of a major and thick AptianTuronian extensional basin (Figs.…”

“…In the southern part of the Chemsi anticline, active shortening is accommodated by a N-verging back-thrust which connects down with the basement-sedimentary cover interface (Figs. 6c and 12; Gharbi et al, 2014). This back-thrust, located along the Chemsi anticline front, deforms Coniacian-Santonian beds on MiocenePliocene deposits and a Quaternary terrace (Gharbi et al, 2014).…”

“…6c and 12; Gharbi et al, 2014). This back-thrust, located along the Chemsi anticline front, deforms Coniacian-Santonian beds on MiocenePliocene deposits and a Quaternary terrace (Gharbi et al, 2014).…”

“…Plio-Quaternary syntectonic sequences (Zargouni and Termolières, 1981;Ahmadi et al, 2013;Gharbi et al, 2014) correspond to massive conglomerates with sands and gypsum intercalations of Segui Formation (Burollet, 1956;Mannaï-Tayech, 2009) (Figs. 3 and 4).…”

“…The Alpine shortening is considered as a major event which is characterized by a regional mean of NW-trending main regional compression direction (Zargouni and Trémolières, 1981;Dlala, 1992;Chihi, 1992;Bouaziz et al, 2002) during the late MiocenePliocene and N-trending tectonic regime during the late Pliocene-Quaternary (Gharbi et al, 2014). The presence of coarse alluvial fan deposits with growth strata geometry in the northern flank of the Aïn Bou Smaïl syncline (Fig.…”