EVIDENCE FOR A NEOPROTEROZOIC VOLCANIC ARC ACTIVITY IN THE WESTERN HIGH ATLAS (MOROCCO)

In the western High Atlas, major volcanic activity supplied andesitic and dacitic lava and pyroclastic flows interbedded with pelitic sandst ones and limestones. All these formations were isoclinally folded and metamorphosed into the greenschist facies, very likely during the Pan- African orogeny. The lavas include: 1) a few back-are basin basalts de pleted in the most incompatible elements, 2) andesites weakly to moder ately enriched in incompatible elements, and 3) dacites. This magmatis m is assigned to a volcanic are context, which we consider as being ea rlier than the continental intra-plate extensive context of the Cambri an magmatism. ((C) Academie des sciences / Elsevier, Paris.).