THE WESTERNMOST TETHYAN MARGINS IN THE RIF BELT (MOROCCO)

The Rif belt forms the westernmost segment of the Maghrebides and the southern branch of the Gibraltar Arc, whereas the Betic Cordilleras make up the northern branch. This orocline extends in a complex area of triple junction between the Central Atlantic and the two branches of the westernmost Tethys, i.e., the E-NE trending Ligurian-Maghrebian Tethys and its Betic branch (West Ligurian Tethys). The Gibraltar Arc represents the western termination of the peri-Mediterranean Alpine orogenic systems. This orogen formed during the Alpine Mesozoic-Cenozoic convergence between Africa and Eurasia associated with subduction of the westernmost Tethys lithosphere of the northwestern African plate. Our presentation focusses on the remains of the Maghrebian Tethys hyperextended margins and Ocean-Continent Transition (OCT) domains, that are exposed in the Rif Belt. The southern OCT of the Maghrebian Tethys (Rif External zone) consist of serpentinites and gabbros slivers included in the accretionary prism derived from the inversion of the African passive margin. The northern margin of the Maghrebian Ocean is classically represented by the Dorsale Calcaire and Predorsalian Triassic-Paleogene units at the external border of the Internal Zones (Alboran Domain). The latter mainly consists of two complexes of basement nappes, from top to bottom, the Ghomarides, and Sebtides complexes ((Malaguides and Alpujarrides in Spain, respectively). The Dorsale sedimentary units are transitional between the Ghomarides-Malaguides coeval sequences and the Maghrebian Flyschs deposits. However, they have been likely detached from the underlying Sebtides-Alpujarrides thinned crust domain. In the lower Sebtides nappes, The Beni Bousera peridotites (Rif equivalent of the Ronda peridotites of the Betic) are capped by a granulites (Kinzigites) envelope, which is in turn overlain by low-pressure, high-temperatures (LP-HT) gneisses. We describe marbles slivers derived from protoliths of probable Triassic age in between the HP and HT crustal units. The mantle rocks would have been exhumed close to the surface as early as the Triassic. In contrast with the usual interpretation of the Gibraltar Arc subcontinental peridotites as mantle rocks basically exhumed during the Alpine cycle, we argue that the record the Triassic incipient formation of a Jurassic hyperextended margin at the northern border of the Maghrebian Tethys.

Keywords: Tethys, North African Transform, Hyperextended margins, Mantle rocks, Oceanic core complexes, Exhumation, Orogenic wedge.