The Tibesti Mountains are a large area of tectonic uplift that, according to contemporary theory, resulted from a mantle plume in the craton of the African lithosphere, which is about thick. This tectonic uplift may have been accompanied by the opening, and subsequent closure via subduction, of a rift zone. The heart of the Tibesti is composed of schist, basalt and diorite of the Ediacaran period, one of six exposures of Precambrian crystalline rock in North Africa. These are overlaid by sandstone of the Paleozoic era, while the peaks consist of volcanic rock.