Active fault segmentation in Northern Tunisia

Abstract

Active shortening structures in Northern Tunisia have developed by tectonic inversion since the Pliocene, after Late Miocene extensional collapse of the whole region. Restored Plio-Quaternary deformation observed on reflection seismic lines indicates deformation rates around 0.6–0.8 mm/yr in the studied segments and larger amounts of shortening to the West of Northern Tunisia (16%) than to the East (7%), which suggests tectonic inversion started earlier to the West and later propagated eastwards, reaching Northeastern Tunisia in the Late Pliocene. This shortening is registered on striated pebbles in Quaternary alluvial terraces and fault-slip data giving two populations of strain ellipsoids with N–S and WNW-ESE maximum shortening. Morphometric analysis in combination with field fault segmentation mapping show that topographic uplift and drainage rejuvenation occurs in relation to 20–30 km long ENE-WSW reverse fault segments and related antiforms that are offset and linked by E-W to WNW-ESE dextral and NE-SW-oriented sinistral faults. The largest fully linked fault system is the Alia-Thibar fault. This 130 km long fault zone shows an helicoidal geometry with five different fault segments, including reverse, dextral, sinistral and oblique faults. Due to the young age of tectonic inversion, after late Miocene extensional collapse of the region, the present relief of Northern Tunisia is characteristic of a young thrust and fold belt, with dominating axial valleys along synforms and an incipient transverse drainage development propagating from West to East.