TUNISIA STRUCTURAL EXTRUSION REVEALED BY NUMERICAL GEOMORPHOMETRY

Neotectonics is revealed by detailed numerical geomorphic analyses of the topography. Tunisia is an excellent case example for this, as it is affected by active tectonics as hit by numerous earthquakes and present faults and folds and associated structural features. Key geomorphic treatments deduced from the bibliography and new indicators developed throughout this study, processed numerically through home made geodatabase, lead us to propose a new structural scheme revisiting the Tunisian tectonic setting. We propose herein an eastern extrusion model of Central Tunisia due to the northward migration of African plate toward Eurasia. On this model deduced from drainage analyses, drainage network classifications, specific analyses of the Digital Terrain Model (DTM), summit level surface analyses and so on integrated within a GIS (Deffontaines, 1990; Deffontaines et al, 1994; Deffontaines 2000; Slama, 2008), and taken into account previous works (Sokoutis D. et al., 2000; Bouaziz S., et al., 2002...), we propose that the well known diapir fault line (Medjerda-Tunis fault zone) correspond to a major left lateral transtensive northeastward fault zone acting as the northern major boundary of the Central Tunisia extrusion. It appears in the fields as a compressive structure linked to the beahaviour of the continuous uplifting of the elongated NE-SW salt diapirs that parallel this major transcurrent extrusion tectonic line. It is associated with the NW-SE trending well known Gafsa-Gabes fault zone which is characterized by numerous en echelon folds acting as a major right lateral fault zone that bounds the southern part of the central Tunisia extrusion (see fig.1 modified from Bouaziz et al, 2002). Within the extruded central Tunisia, the North-South axis also known as Al Abiod N-S fault zone appear to be a reactivated graben closely associated with the eastern extrusion of central tunisia and differenciating high Atlasic and low eastern tunisian Domain (Bouaziz et al, 2002). The major limits of this geomorphic approach is linked to the difficulty to distinguish the different tectonic phases within the long northward African plate migration as the topography reveals cumulated effects. But an expert system (see Slama Tarek et al. 2008) work in progress give excellent perspectives to this approach. Therefore, geomorphometry appears to be an excellent tool at the regional scale in order to better understand the geodynamic setting of this NE part of northern Africa where the African-Eurasian collision is characterized by an eastern extrusion of the central part of Tunisia. Numerous perspectives prevail on seismic hazards, neotectonics, and understanding of the past structural history. Further works is proposed in order to monitor bathymetry, gravimetry, magnetism and a quick seimic refelction survey offshore in order to locate the exact prolongation of the Tunisian extrusion major tectonic lines. References : Bouaziz S., Barrier E., Soussi M., Turki M.M., Zouari H., 2002. Tectonic evolution of the northern African margin in Tunisia frompaleostress data and sedimentary record, Tectonophysics, 357: 227-253. Sokoutis D., Bonini M., Medvedev S., Boccaletti M., Talbot C.J., Koyi H., 2000. Indentation of a continent with a built-in thickness change: experiment and nature. 320: 243-270.