Tectonic Evolution of the Active "Chelif" Basin (Northern Algeria) from Paleomagnetic and Magnetic Fabric Investigations

Abstract

The present-day crustal deformation in the North African area is mainly driven by the NWSE to NNW–SSE convergence (4–5 mm/yr) between the African and Eurasian plates (Mckenzie, 1972; Nocquet & Calais, 2004; Serpelloni et al., 2007). This convergence is accommodated over a wide deformation (the Tellian Atlas) implying the existence of significant seismic activity. This domain represents the southern part of the Alpine ranges at the boundary between the African and Eurasian plates. It is characterized by E-W to NE-SW trending folds and thrust belt and composed by an external zone with Mesozoic to Tertiary rocks and an internal zone consisting of a thrust stack of metamorphic complexes and Mesozoic calcareous and flysch. Overlying these previous series, Neogene to Quaternary sediments fill the intramountainous basins, limited by E–W and NE–SW faults as evidenced in the “Chelif” basin (Chiarabba et al, 1996; Meghraoui, 1982; Meghraoui, 1988; Thomas, 1985). Few studies were dedicated to these faults (Aoudia & Meghraoui, 1995; Chiabbara et al., 1996; Meghraoui, 1988; Phillip & Meghraoui, 1983), consequently the timing and amount of displacement of these faults, as well as their relationship with the Neogene basin development, are still a matter of debate (Thomas, 1985; Neurdin-Trescartes, 1992; Belkebir et al., 1996; Bessedik et al., 2002). The seismic activity is mainly characterized by moderate to destructive magnitude events as it was shown by the recent 21 May 2003 Zemmouri earthquake (Mw=6.8) (Meghraoui et al., 2004) and the 10 October 1980 El Asnam (presently Chlef) earthquake (Mw=7.3) (Ouyed et al.,1981). These two earthquakes are the strongest recent ones that occurred in this part of Western Mediterranean area. According to the Algerian earthquake catalogue (Benouar, 1994) the earthquake activity is mainly concentrated in the intramountainous seismogenic basins which belongs to the Tellian Atlas. The convergence movement between Africa and Eurasia plates involves a tectonic transpression with N-S to NNW-SSE direction, which initiate faulting activity along “en echelon” NE-SW trending folds and associated reverse faults. This “en echelon” system