Abstract
Abstract A swarm of granite massifs outcrops in the Pharusian structural basin of western Ahaggar (Algeria) not far from the major dislocation marking the eastern boundary of the basin, and separating two distinct areas. The granites appear as ring structures; two phenomena caused these features: the emplacement of several successive porphyroid granites, each one having identical composition but varying in grain size, and the formation of thick rings with relatively alkaline and leucocratic borders. Two generations of massifs are apparent and differ in their alkaline marginal facies, in their complexity, and in their geographic situation. The plutons of western Ahaggar and the subvolcanic structures of Nigeria have certain aspects of their structure in common. Nevertheless, the 'taourirts' are older and less evolved than those of Nigeria.
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