Abstract
The Tell-Rif (Tell in Algeria and Tunisia; Rif in Morocco) is the orogenic system fringing to the south the West Mediterranean basins. This system comprises three major tectonic-palaeogeographic zones from north to south: (1) the internal zones (AlKaPeCa for Alboran, Kabylies, Peloritan, Calabria) originating from the former northern European margin of the Maghrebian Tethys, (2) the “Flyschs zone” regarded as the former cover of the oceanic domain and (3) the external zones, forming the former southern Maghrebian Tethys margin more or less inverted. The Tell-Rif is interpreted as the direct result of the progressive closure of the Maghrebian Tethys until the collision between AlKaPeCa and Africa and, subsequently, the propagation of the deformation within Africa. This gives a consistent explanation for the offshore Neogene geodynamics and most authors share this simple scenario. Nevertheless, the current geodynamic models do not completely integrate the Tell-Rif geology. Based on the analysis of surface and sub-surface data, we propose a reappraisal of its present-day geometry in terms of geodynamic evolution. We highlight its non-cylindrical nature resulting from both the Mesozoic inheritance and the conditions of the tectonic inversion. During the Early Jurassic, we emphasize the development of NE-SW basins preceding the establishment of an E-W transform corridor connecting the Central Atlantic Ocean with the Ligurian Tethys. The Maghrebian Tethys developed just after, as the result of the Late Jurassic-Early Cretaceous left-lateral spreading between Africa and Iberia. By the Late Cretaceous, the occurrence of several tectonic events is related to the progressive convergence convergence between the two continents. A major pre-Oligocene (pre-35 Ma) compressional event is recorded in the Tell-Rif system. The existence of HP-LT metamorphic rocks associated with fragments of mantle in the External Metamorphic Massifs of the Eastern Rif and Western Tell shows that, at that time, the western part of the North-African margin was involved in a subduction below a deep basin belonging to the Maghrebian Tethys. At the same time, the closure of the West Ligurian Tethys through east-verging subduction led to a shift of the subduction, which jumped to the other side of AlKaPeCa involving both East Ligurian and Maghrebian Tethys. Slab rollback led to the development of the Oligo-Miocene back-arc basins of the West-Mediterranean, reworking the previous West Ligurian Tethys suture. The docking of AlKaPeCa against Africa occurred during the Late Burdigalian (17 Ma). Subsequently, the slab tearing triggered westward and eastward lateral movements that are responsible for the formation of the Gibraltar and Tyrrhenian Arcs respectively. The exhumation of the External Metamorphic Massifs occurred through tectonic underplating during the westward translation of the Alboran Domain. It resulted in the formation of both foredeep and wedge-top basins younger and younger westward. The lack of these elements in the eastern part of the systems signs a different evolution dominated by frontal accretion. In the discussion, we precisely address the origin of the non-cylindrical behavior of the orogenic system and question the mechanisms explaining at large scale the phases of coupling/uncoupling between the major plates.
Highlights
The existence of high pressure-low temperature (HP-LT) metamorphic rocks associated with fragments of mantle in the External Metamorphic Massifs of the Eastern Rif and Western Tell shows that, at that time, the western part of the North-African margin was involved in a subduction below a deep basin belonging to the Maghrebian Tethys
The closure of the West Ligurian Tethys through east-verging subduction led to a shift of the subduction, which jumped to the other side of AlKaPeCa involving both East Ligurian and Maghrebian Tethys
This consensus has been recently broken by Vergés and Fernàndez (2012) followed by Casciello et al (2015), who propose a completely different model. Their model suggests that Alboran was initially located along the African margin and separated from the Kabylie, which, together with the Calabrian and Peloritan terranes, were on the European side of the Maghrebian Tethys. This provocative proposition is interesting but disregards several geological evidences: À the strong palaeogeographic affinities between Alboran and the Kabylie during the whole Mesozoic, especially during Triassic time, these two domains being characterized by “Alpine” facies contrasting with the “Germanic” facies which characterize both African and Iberian margins (Bouillin, 1986; Durand-Delga, 1969); À offshore data (Booth-Rea et al, 2007; Medaouri et al, 2014), suggesting rather WSW than NW movements of the Alboran Domain; À seismic data showing that Kabylie-like terranes can be currently followed offshore up to the Oran meridian (Domzig et al, 2006), i.e. in the assigned root zone of Alboran in the Vergés and Fernàndez (2012) model
Summary
The West Mediterranean back-arc basins developed since the Oligocene in relation with the roll-back of the subduction of the Ligurian-Maghrebian Tethys (LMT) (Bouillin, 1986; Doglioni et al, 1999; Frizon de Lamotte et al, 2000; Gueguen et al, 1998; Jolivet and Faccenna, 2000; Jolivet et al, 2008; Lonergan and White, 1997; Malinverno and Ryan, 1986; Réhault et al, 1984; Vergés and Sàbat, 1999; Fig. 1). Their model suggests that Alboran was initially (i.e. during the Mesozoic) located along the African margin and separated from the Kabylie, which, together with the Calabrian and Peloritan terranes, were on the European side of the Maghrebian Tethys This provocative proposition is interesting but disregards several geological evidences: À the strong palaeogeographic affinities between Alboran and the Kabylie during the whole Mesozoic, especially during Triassic time, these two domains being characterized by “Alpine” facies contrasting with the “Germanic” facies which characterize both African and Iberian margins (Bouillin, 1986; Durand-Delga, 1969); À offshore data (Booth-Rea et al, 2007; Medaouri et al, 2014), suggesting rather WSW than NW movements of the Alboran Domain; À seismic data showing that Kabylie-like terranes can be currently followed offshore up to the Oran meridian (Domzig et al, 2006), i.e. in the assigned root zone of Alboran in the Vergés and Fernàndez (2012) model. Key geodynamics consequences of our review will be discussed at the end of this contribution
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