The Central High Atlas of Morocco has been the site of an extensive transitional to alkali mafic magmatism from Middle Jurassic (B1 event) to Lower Cretaceous (B2 event). This study presents petrographical, mineralogical, geochemical and Sm-Nd isotopic investigations of mafic dykes and basaltic flow from the “ Plateau des lacs ” syncline, Central High Atlas, in order to characterize the geochemical features of the magmas and constrain their genesis. The primary paragenesis of basic rocks remains invariable with olivine (Fo 65%–87%), clinopyroxene (augite and/or diopside), plagioclase (An 10 to An 55 ), opaque minerals (spinel, ulvospinel and ilmenite) and minor apatite. Orthopyroxene (63%–87% En) occurs in basaltic flows but is rare in mafic dykes. This represents the first report of this mineral in the magmatism of the Central High Atlas and suggests crystallization from parental magmas already modified by fractional crystallization under relatively high-pressure conditions at considerable depth, likely near the crust–mantle boundary. The geochemical and mineralogical features of this magmatism, using immobile elements, indicate intraplate alkaline to transitional basalts with ocean-island basalts (OIB)-like trace-element signatures, interpreted as evolved derivatives of mantle-derived magmas produced by low-degree partial melting of a garnet-bearing source. These magmatic rocks show positive εNd (+2.15 to +4.84) and Nd-TDM ages ranging from 0.48 to 0.83 Ga, which confirms their mainly juvenile parental magma derived from depleted asthenospheric mantle source. These results are discussed in the framework of Jurassic intraplate magmatism associated with lithospheric thinning and asthenospheric mantle upwelling beneath the evolving Central High Atlas rift system.
Nachit et al. (Wed,) studied this question.