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.

Active Faulting Geometry and Stress Pattern Near Complex Strike‐Slip Systems Along the Maghreb Region: Constraints on Active Convergence in the Western Mediterranean

“…Based on tectonic reconstitutions, seismic tomography, geological, and geophysical evidence (Argnani, 2009;Booth-Rea et al, 2018;Govers & Wortel, 2005;Jolivet et al, 2009;Lucente & Margheriti, 2008;Wortel et al, 2009), we suggest a primary role of the first-order preexisting weak zones in the western Mediterranean, in particular the so-called Slab Transfer Edge Propagator (STEP) fault in the active geodynamics of the Maghreb. Near this E-W major transform fault system, along the Tell domain, there is a mix of reverse and strike-slip focal mechanism solutions (Figure 2a).…”

“…The stress inversion result of the largest‐magnitude focal mechanism solutions reveals a strike‐slip tectonic regime with slight reverse component ( R ′ = 1.65 ± 0.12) and N148°E ± 6.9° S Hmax (Table ). In fact, within this part of interplate shear zone (Booth‐Rea et al, ), the seismic activities and focal mechanism solutions show a reactivation of the E‐W deep‐seated south Atlasic preexisting fault with strike‐slip motion (in its eastern part) and its tip damage zones. This is in agreement with strike‐slip to transpression‐compatible paleostress results obtained for the neotectonic period (Soumaya et al, ; Vially et al, ).…”

Lithosphere tearing along STEP faults and synkinematic formation of lherzolite and wehrlite in the shallow subcontinental mantle

“…3-D tomographic imaging of the mantle structure reveals a steeply east-dipping slab under the Strait of Gibraltar with a slab morphology that extends from under the Rif towards the north and then curves eastward under the Betics (e.g., Spakman and Wortel, 2004;Gutscher et al, 2012;Bezada et al, 2013;van Hinsbergen et al, 2014). These works also show a detached slab beneath the Kabylides in northeast Algeria (Spakman and Wortel, 2004;Faccenna et al, 2014;van Hinsbergen et al, 2014), which is interpreted as a part of the Algerian-Tunisian slab separated from the Betic-Rif slab system by STEP faults (Booth-Rea et al, 2018a). The present-day Betic-Rif slab morphology is consistent with the evolution of an initially NW-dipping subduction zone situated southeast of the Balearic Islands in the Oligocene that retreated towards the south and later to the west, after approximately 90 • clockwise rotation, during the Miocene to reach its current position beneath the Strait of Gibraltar (e.g., Royden, 1993;Lonergan and White, 1997;Rosenbaum et al, 2002;Spakman and Wortel, 2004;Chertova et al, 2014a, b;van Hinsbergen et al, 2014).…”

“…1a) (Turner et al, 1999;Duggen et al, 2004Duggen et al, , 2005, and references therein). Actually, the eastern Alboran basin basement is formed by a submerged well-developed volcanic arc (Booth-Rea et al, 2018b;Gómez de la Peña et al, 2018). Meanwhile, at the west Maghrebian and southeast Iberian continental margins, this late Miocene magmatism was coeval to extensional collapse and thinning of the previously thickened orogenic crust (e.g., Booth-Rea et al, 2012;Giaconia et al, 2014;Jabaloy-Sánchez et al, 2015;Azdimousa et al, 2019) and loss of its SCLM root (Duggen et al, 2003;Mancilla et al, 2015).…”

Lithosphere tearing along STEP faults and synkinematic formation of lherzolite and wehrlite in the shallow subcontinental mantle

“…al., 2013;van Hinsbergen et al, 2014). These works also show a detached slab beneath the Kabylides in northeast Algeria (Spakman and Wortel, 2004;Faccenna et al, 2014;van Hinsbergen et al, 2014), which is interpreted as a part of the Algerian-Tunisian slab separated from the Betic-Rif slab system by STEP faults (Booth-Rea et al, 2018a). The present-day Betic-Rif slab morphology is consistent with the evolution of an initially NW dipping subduction zone situated southeast of the Balearic islands in the Oligocene that retreated towards the south and later to the west, after approximately 90º clockwise rotation, during the Miocene to reach its current position beneath the Gibraltar strait (e.g., Royden, 1993;Lonergan and White, 1997;Rosenbaum et al, 2002;Spakman and Wortel, 2004;Chertova et al, 2014a;Chertova et al, 2014b;van Hinsbergen et al, 2014).…”