Air, Niger
Location: 17.67N, 8.75E
The Air Mountains make up one of the largest ring dike
structures in the world. This Precambrian massif is
famous for magmatic ring
complexes 50 miles (80 km) in diameter.
Ring-dikes, stocks and batholiths run 342 miles
(550 km)
from north to south. Some intrusions are over 19 miles (30 km) wide.
Todra, the center of the massif, is surrounded by 100 basaltic
strombolian cones and phreatomagmatic tuff rings. It
is made of differentiated alkali lavas consisting of plugs and flows of
hawaiite to trachyte.
The dark, roughly circular masses are Cenozoic lava flows on
sandstones and schists. The crater at the lower left would appear to be
of volcanic origin in view of its nearness to the lava flows. This area
is capped by sandstone. The picture gives an excellent view of the
general geology and structure of the uplift as a whole.
--Paul D. Lowman Jr.
PhD. NASA
Sources:
Dautria, J.M. and Girod, M., "Cenozoic volcanism associated with swells
and rifts," Mantle Xenoliths, John Wiley & Sons Ltd., pp. 195-214, 1987.
Green, Jack and Short, Nicholas, "Volcanic Landforms and Surface
Features," Springer-Verlag, New York, 519 pp., 1971.
Grove, A.T., "Geomorphology of the Tibesti Region with Special Reference
to Western Tibesti," pp. 18-31.
"Earth Resource Surveys From Spacecraft," US Army Corps of Engineers,
vol. 2, photo Gemini GB-58, p. E-50.
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