|The Azores are shown as hot spot volcanoes on some maps but physical and chemical evidence shows they are associated with a spreading center. Searle (1980) presented an excellent study on the history of the Azores triple junction, the area where the North American (shown as N.A. Plate), Eurasian, and African plates meet at a point. Triple junctions can have any shapes but "T" or "Y" shapes are most common. Near the Azores the three plates meet to form a T-shaped triple junction. The Mid-Atlantic Ridge forms two legs of the "T". Searle showed that the third leg is the Azores spreading center. This spreading center (called the Terceira Rift) is made of a series of en echelon rifted basins. The spreading center formed about 36 million years ago and has been migrating to the south. The Azores lack a linear progression in the age of the volcanoes, a trend common in volcanoes associated with hot spots. Map modified after Moore (1990).|
Flower and others (1976) looked at the geochemistry of lavas from five islands in the Azores. They found no chemical evidence for the presence of a mantle plume in the source region of the basalts.
Flower, M.F.J., Schmincke, H.-U., and Bowman, H., 1976, Rare earth and other elements in historic Azorean lavas: Journal of Volcanology and Geothermal Research, v. 1, p. 127-147.
Moore, R.B., 1990, Volcanic geology and eruption frequency, Sao Miguel, Azores: Bull. Volcanology, v. 52, p. 602-614.
Searle, R., 1980, Tectonic pattern of the Azores spreading centre and triple junction: Earth and Planetary Science Letters, v. 51, p. 415-434.
Simkin, T., and Siebert, L., 1994, Volcanoes of the World: Geoscience Press, Tucson, Arizona, 349 p.
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