Ali Saquaque

Precambrian accretionary tectonics in the Bou Azzer-El Graara region, Anti-Atlas, Morocco

Ophiolites of the Anti-Atlas of Morocco occur as highly dismembered slivers of mafic and ultramafic rocks sandwiched between a Precambrian craton and a magmatic arc. Tectonic slices of accretionary melange, ophiolites, and forearc basins have been juxtaposed by oblique subduction and transpression in the forearc region of a Late Proterozoic subduction zone. Synkinematic to postkinematic calc-alkalic magmatism in these terranes indicates migration of the magmatic front over the deformed forearc terranes.

Anti-Atlas (Morocco) role in Neoproterozoic Western Gondwana reconstruction

Abstract Reconstruction of latest Neoproterozoic Gondwana hinges on the interpretation of the subduction and collision kinematics of Pan-African orogenic belts that rim the West African craton. The Anti-Atlas suture zone of southern Morocco has presented an enigma in this reconstruction as the inferred subduction zone polarity and age of suturing appear to be incongruous with better known West African orogens to the west (Mauretanian, Bassaride and Rokelide) and Transaharan orogens to the east (Ougarta, Tuareg, Gourma and Dahomeyan). Contrary to previous interpretations, new data from the Anti-Atlas indicate a history of late Neoproterozoic (∼750–600) north-dipping subduction culminating in the (∼600 Ma) collision of the Saghro magmatic arc to the north with the north-facing rifted margin of the West African craton. Thus, the Anti–Atlas suture links a ∼6000-km long chain of Pan-African suture zones that essentially encircle the West African craton. The suture zones demarcate the former position of subduction zones that in all cases dipped away from the West African craton. The Anti-Atlas suture links the western and eastern segments of the Pan-African orogenic belts associated with the amalgamation of Western Gondwana.

Proterozoic collisional basins in a Pan-African suture zone, Anti-Atlas Mountains, Morocco

Abstract The Anti-Atlas Mountains constitute a Late Proterozoic suture zone produced by northward subduction of oceanic lithosphere culminating in the Pan-African orogeny. Southward migration of thrust slices associated with the destruction of the forearc terrane resulted in the uplift and erosion of previously deposited basin sediments. These sediments were subsequently reincorporated into collisional basin deposits of the Tiddiline Formation. The Tiddiline Formation consists of coarsening-upwards sequences of maroon siltstones, sandstones and intraformational conglomerates. These rocks unconformably overlie metamorphosed volcaniclastic rocks of the relict forearc basin and accretionary terrane. Syn- and post-depostional deformation has resulted in folding about gently-plunging fold axes. Folds were subsequently cut by strike-slip faults that strike at a high angle to the basin axis. Deformation of the Tiddiline Formation is attributed to transpressional suturing of the relict forearc terrane to the West African Craton to the south. Collisional basins of the Anti-Atlas Mountains serve as ancient analogs for the destruction of forearc basins in an obliqueconvergent margin setting, such as those of the Western Pacific region.

Proterozoic blueschist-bearing mélange in the Anti-Atlas Mountains, Morocco

Abstract Blueschists from the Bou Azzer inlier provide compelling evidence for Late Proterozoic subduction in the Anti-Atlas Mountains of Morocco. High-pressure/low-temperature metabasites containing blue amphibole minerals crossite and magnesioriebeckite record pressures in excess of 5 kbar. Together with regional relationships, the geologic setting of the blueschists constrains the polarity of Pan African subduction in this region, which occurred from ∼750 to 600 Ma. Blueschist facies rocks crop out in a heterogeneous assemblage of variably deformed and metamorphosed tectonic slices of ophiolitic fragments enclosed in a schistose serpentinite matrix. The melange belt containing the blueschist facies rocks is intruded by a number of diorite plutons, one of which has yielded a U/Pb radiometric age of 650 Ma. Together with Transaharan Belt to the southeast, the Anti-Atlas suture zone exposed within the Bou Azzer inlier contains among the oldest known blueschist-bearing, ophiolitic melanges in the world.