Late Miocene Extensional Collapse of Northern Tunisia

Abstract

Two orthogonal extensional systems produced the extensional collapse of the Tell and Atlas thrust belts in northern Tunisia during the Late Miocene to Pliocene in a context of NW-SE plate convergence between Africa and Eurasia. The older extensional system shows several low-angle normal faults (LANFs) and associated high-angle faults with ENE-directed transport that produced half-grabens and hanging-wall syncline basins during the late Tortonian to Messinian. The direction of extension swinged towards the SE during the Messinian, cutting into, and tilting the previous detachments. Extension was accompanied by the extrusion of 8-Ma rhyodacites and Messinian basalts, together with the development of mineralized fault breccias. Plio-Quaternary NW-SE directed shortening formed inversion arrowhead structures, reverse faults, refolded extensional rollover anticlines and folded the LANFs. ENE-directed extension is concomitant with the opening of the Tyrrhenian basin. We consequently think that both processes are related and that tearing of the Calabrian slab along the northern Tunisia coast drove the ENE-directed extension. Meanwhile, the SE-directed extension that followed was probably related to SE-directed peeling back of the Tunisian continental lithospheric mantle during NW subduction of the Maghrebian margin. This extension propagated eastwards from the late Tortonian until the Pliocene following the SE migrating subduction front and favored by lateral slab tearing along the Tunisian Atlas dextral Subduction Transfer Edge Propagator boundary. This new hypothesis for the tectonic evolution of northern Tunisia shows for the first time the importance of crustal extension in the denudation of the Tunisian Atlas and Tell foreland thrust belts and its relation to deep mantle tectonic mechanisms.