Sur quelques caracteres du volcanisme precambrien dans la region de Silet (Ahaggar occidental, Sahara central)

Abstract In the region of Silet (western Ahaggar, central Sahara) two major volcanic episodes predating the deposition of the Cambro-Ordovician Tassilis sandstone are identified. They are definitely pre-Tremadoc (uppermost Cambrian or lowermost Ordovician) and are probably both Precambrian. The volcanic rocks of the Timesselarsine series (lower series) are apparently the result of submarine volcanism, while the volcanic rocks of Adrar Irellouchem (upper series) originated during subaerial or continental volcanism. All of these volcanic rocks seem to have been derived from calc-alkaline magmas of the Pacific type, which are characteristic of folded ranges.