From the Hercynian orogenic cycle towards the central Atlantic prerifting in central Morocco: are the Jbilet microdiorites possible magmatic markers for this transition?

Microdioritic intrusives crosscut the Hercynian structures of the Jbilet ma ssif in the western Morocco. Their mineralogical, petrological and geochemi cal compositions display the main characteristics of calc-alkaline magmas a nd any of the alkaline ones. This magmatic event occurred at ca 255 Ma, as indicated by the K-40-Ar-40 age of fresh kaersutite crystals, but seven age s for whole-rock samples. scattered between 231 and 180 Ma. reflect the gen eral rejuvenation of the ages linked to a latter penetrative alteration eve nt of their feldspars and groundmass. (C) 2001 Academie des sciences / Edit ions scientifiques et medicales Elsevier SAS.