The Amsterdam-St. Paul volcanic province,and the formation of low Al tholeiitic andesites |
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| Authors: | Bernard M Gunn Norman D Watkins Walter E Trzcienski Jacques Nougier |
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| Institution: | 1. Department of Geology, Université de Montréal, Montréal, Québec, Canada;2. Graduate School of Oceanography, University of Rhode Island, Kingston, Rhode Island, 02881, USA;3. Départeent de Génie Minéral, Ecole Polytechnique, Montréal, Québec, Canada;4. Science Faculty, Federal University, Yaounde, Cameroons, West Africa |
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| Abstract: | The island of St. Paul in the Indian Ocean is located on the axis of the southeastern branch of the Indian Ocean Rise, as is the similar volcano of Amsterdam, 80 km to the north. Both volcanoes and possibly part of the local ridge are formed of a high-alumina plagioclase tholeiite making this a distinctive volcanic province. Lavas with Al2O2 contents of 12 to 22% are directly related by plagioclase fractionation. Residual rocks are a distinctive low silica, low alumina, potassic andesite with andesine and even olligoclase feldspar. Parallel lines of evolution exist in the sea floor plagioclase tholeiites, which differ only in slightly lower tenor of Sr and potassium group elements, and in the Steens Mountain tholeiites of Oregon, which differ in their significantly higher Sr and K group elements |
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