Oceanic units in the core of the External Rif (Morocco): Intramargin hiatus or South-Tethyan remnants? - BRGM - Bureau de recherches géologiques et minières Accéder directement au contenu
Article Dans Une Revue Journal of Geodynamics Année : 2014

Oceanic units in the core of the External Rif (Morocco): Intramargin hiatus or South-Tethyan remnants?

Résumé

he aim of this paper is to describe the mafic rocks that crop out in the central-western Mesorif Zone (External Rif Belt), and discuss their geodynamic signification. Basalt flows, olistoliths and breccias occur in Oxfordian-Berriasian deposits of Mesorif units ascribed to the distal part of the African paleomargin. The climax of volcanic activity is observed at the northern border of a Kimmeridgian carbonate platform progressively dismembered during the Tithonian-Berriasian. In spite of the alteration of the basalts, their petrological and geochemical characters point to E-MORB affinities. The studied gabbro massifs (Bou Adel, Kef el Rhar west and north) occur as restricted slivers or klippes within the Senhadja nappe or melange of the internal Mesorif, which overlies the basalt-bearing units and other, more external Mesorif units. The compositions range from troctolitic olivine gabbro to ferrogabbro with frequent ortho- to heteradcumulate textures; they display typical tholeiitic affinity. The gabbro massifs are crosscut by trondjhemite dykes and overlain by metabasalts, fault-scarp breccias, ophicalcites, marbles and radiolarites. Composition featuring initial near liquid composition, display multi elements patterns close to those of E-MORB, with a weak Eu negative anomaly and evidence of slight crustal contamination. These gabbro massifs were regarded as Jurassic-Cretaceous intrusions, locally dated (K-Ar) at 166 +/- 3 Ma. Conversely, we assume they represent discrete samples of a Jurassic-Cretaceous oceanic basement (ophiolites), emplaced tectonically in the Senhadja nappe (melange) of the central Mesorif. The correlation of both these types of mafic rock associations (paleomargin basalts and ophiolite klippes) with the serpentinites of the eastern Mesorif (Beni Malek) and Oran mountains (Algeria) is then briefly discussed. We conclude that the previous hypothesis of an intramargin "Mesorif suture zone" must be reconsidered, being challenged by that of a major, syn-collisional "Oran-Mesorif Strike-Slip Fault". In the latter hypothesis, the newly described Mesorif oceanic klippes would represent allochthonous remnants of the Ligurian-Maghrebian (Tethyan) oceanic domain.
Fichier non déposé

Dates et versions

hal-01176398 , version 1 (15-07-2015)

Identifiants

Citer

Mohamed Benzaggagh, Abdelkader Mokhtari, Philippe Rossi, André Michard, Abdelkhader El Maz, et al.. Oceanic units in the core of the External Rif (Morocco): Intramargin hiatus or South-Tethyan remnants?. Journal of Geodynamics, 2014, 77, pp.4-21. ⟨10.1016/j.jog.2013.10.003⟩. ⟨hal-01176398⟩

Collections

BRGM
66 Consultations
0 Téléchargements

Altmetric

Partager

Gmail Facebook X LinkedIn More