Premières données géochronologiques sur le volcanisme alcalin du Jbel Saghro, Anti-Atlas, Maroc

The Jbel Saghro is one of the two late Cenozoic, large volume strato-volcano of the so-called Anti-Atlas. Saghro (east) and Siroua (west) lie within a zone of local extension but in a regional context of compression, related to a major E-W fault system that defines the southern rim of the Haut-Atlas. The tectonic regime is trans-tensional.

Lavas composition range from olivine nephelinites to phonolithes, but major and trace element criteria permit distinctions between one group which includes only phonolites versus a separate more diverse group which includes nephelinites and phonolites. K-Ar dating of 22 whole rock samples demonstrate a temporal-spatial progression from early volcanism in the centre of the area (10-6.4 Ma) to activity focused in the northern part of the complex (5.5-2.8 Ma; includes the youngest eruption). The sequence is successively more evolved from nephelinite through tephrite to phonolite, but the younger, northern sequence is confined to olivine-nephelinites.