Geology Of Air Mountains

The Precambrian Aïr Mountains consist of peralkaline granite intrusions which appear dark in colour (unusual since most granitic masses are light-toned in the field). In the Sahara Desert such mountains often stand out in stark relief as topographic heights amidst lowlands covered by sand. The terrain consists of high plateau, mountain ranges, and broad, sandy valleys and seasonal wadis which once contained rivers. Areas of these deep, often intersecting, valleys also contain waterborne clay and silt deposits. Underground watercourses in some of these valleys continue to provide year round oasis and seasonal vegetation.

Circular granite massifs (dark areas). A volcanic crater can be seen at the lower left. NASA image approximately 130 km (80 miles) across.

The Aïr mountains themselves consist of nine almost circular massifs rising from a rocky plateau, bordered by the sand dunes and plain of the Ténéré Desert to the east.

The massif is a plateau consisting of a Cambrian age erosion surface on Precambrian metamorphic rocks, punctuated by a series of flat-topped, granite intrusion peaks, which include Mont Idoukal-n-Taghès (Niger's highest point at 2022 m), Mont Tamgak (1988 m), Mont Greboun (1944 m), Adrar Bous, Fadei, Chirriet, Taghmert, Agueraguer, Takaloukouzet, and Goundai.

The massif contains volcanic features including the extinct caldera of Arakao, Cenozoic lava flows of hawaiite to trachyte composition, volcanic cones, tuff rings and one of the largest ring dike systems in the world.

At Izouzaoenehe, lie the marble Blue Mountains, and the lower Zagado valley is surrounded by white marble hills.

Carboniferous sandstone and coal units in the Iullemmeden Basin just to the west of the massif contain uranium mineralisation sourced from the granites of the massif.