Les coupoles granitiques et rhyolitiques de la region de Fort-Lamy (Tchad)

Abstract

Abstract Describes several rock masses rising above the Quaternary plain of the Chad region (French Equatorial Africa) in the vicinity of Fort-Lamy. East of Fort-Lamy, most of them consist of a cupola of normal granite capped by a columnar zone whose interstices are characterized by rhyolitic facies, above which isolated round masses of granite in rhyolite or, in some cases, pure rhyolite occur, the transition frequently taking place within 20 meters. Northwest of Fort-Lamy, the structures are similar but the rock is almost entirely rhyolitic; one of them certainly is the upper part of a volcano.