A large (70,000 square miles; 180,000 square km) alkali basalt province is located on the Arabian Plate in Saudi Arabia. This volcanism is related to the rifting of the Arabian and African plates and the formation of the Red Sea. Prior to rifting, the area was a stable craton. Volcanism began about 40-50 million years ago as the crust was stretched laterally. Most of the rifting and volcanism has occurred in the last 30 million years. In the last 5 million years, volcanism along the divergent plate boundary beneath the Red Sea has produced tholeitic basalt, similar to basalts at mid-ocean ridge. Simplified from Figure 1. of Thornber (1990).
Volcanism is distributed asymmetrically with respect to the Red Sea. Large areas are covered with basalt on the Saudi Arabian Plate. No volcanism has occurred at similar latitudes on the African Plate. Photo courtesy of the U.S. Geological Survey.
The ages for the volcanic rocks and heat-flow data suggest conditions favorable for producing magma are migrating northeasterly from the present location of the Red Sea spreading axis (Gettings, written communication, 1989 in Thornber, 1990). Cross-section modified from Bohannon and others (1989).
Volcanic vents of the Harrat Hutaymah volcanic province. Numbers indicate locations mentioned in the text.
Arabian geologists call alkali basalt fields harrats. "Harrat" is the possessive form of the Arabic word "harrat", which means "stony area volcanic country or lava field." Numerous harrats are aligned along the west margin of the Saudi Arabian Plate subparallel to the Red Sea.
Harrat Hutaymah is less than 2 million years old, making it one of the youngest volcanic fields in Saudi Arabia. It is also one of the most distant volcanic fields from the Red Sea. The volcanic deposits cover 350 square miles (900 square km) in an area scattered over 950 square miles (2,500 square km). However, Harrat Hutaymah is relatively small compared to other harrats in Saudi Arabia. Xenoliths from the mantle are unusually common at Harrat Hutaymah. The minerals and chemistry of the xenoliths are used to study how the source region of the basalts has changed over time (Thornber, 1990 and 1994). This false color Landsat image shows Harrat Hutaymah. The granitic rocks of Jabal Salma bound the volcanic field on the west. Harrat al Dibadib, the eastern most volcanic cone at Harrat Hutaymah, is at the center of the right margin. Samra as Safra, a tuff ring, is at the bottom of the images just left of center on the bottom. Image courtesy of the U.S. Geological Survey.
Tuff rings and cinder cones are the most common volcanoes at Harrat Hutaymah. Tuff rings are made of poorly consolidated basaltic tephra that dips 5-15 degrees away from the central crater. Tuff rings form when magma comes in contact with water close to or at the surface. The magma and water interact explosively, producing a crater and the surrounding apron of tephra.
The town of Tabah is in a tuff ring. Basaltic cinder cones and flows are on the south rim of the tuff ring. Jabal Salma forms the horizon. Jabal Salma is made of 570-585 million year old granitic plutons that are part of the Arabian-Nubian Shield. View is to the northwest. Photo by Carl Thornber, U.S. Geological Survey.
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Coleman, R.G., 1984, The Red Sea; a small ocean basin formed by continental extensions and sea floor spreading: Proceedings of the 27th International Geological Congress, Moscow, v. 23, p. 93-121.
Coleman, R.G., Fleck, R.J., Hedge, C.E., and Ghent, E.D., 1977, The volcanic rocks of southwest Saudi Arabia and the opening of the Red Sea, in Hilpert, L.S., ed., Red Sea Research, 1970-1975: Saudi Arabian Directorate of Mineral Resources, Bulletin no. 22, p. 1-20.
Coleman, R.G., Gregory, R.T., and Brown, G.F., 1983, Cenozoic volcanic rocks of Saudi Arabia: U.S. Geological Survey Open-File Report OF-03-83, 82 p.
Pallister, J.S., 1987, Magmatic history of Red Sea rifting; perspectives from the central Saudi Arabian coastal plain: Geological Society of America Bulletin, v. 98, p. 400-417.
Thornber, C. R., 1994, Ultramafic inclusions from Harrat Hutaymah: A record of mantle magmatism beneath north central Arabia, in Meyer, H.A.)., and Leonardos, O.H., (eds.), Kimberlites, Related Rocks, and Mantle Xenoliths, 5th International Kimberlite Conference Proceedings Volume, Compania de Pasquisa de Recursos Minerais, Special Publication 92/A, Brazilia, p. 434-454.
Thornber, C. R., 1990, Geologic map of Harrat Hutaymah, with petrologic classification and distribution of ultramafic inclusions, Saudi Arabia: U.S. Geological Survey Map MF-2129.
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