Nature of the clinopyroxene and iron enrichment in alkalic and transitional basaltic magmas |
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| Authors: | F Barberi H Bizouard J Varet |
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| Institution: | (1) Istituto di Mineralogia e Petrografia, University of Pisa, Italy;(2) Laboratoire de Petrographie et Volcanologie, University of Orsay-91, France;(3) Present address: Department of Geology, University of Addis Ababa, P. 0. Box 1176, Ethiopia |
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| Abstract: | Iron enrichment and clinopyroxene composition are considered to be good indicators of the magmatic parentage of volcanic series produced by fractionation of basaltic magma. Tholeiitic series are in fact believed to be constantly more iron enriched than alkalic series and systematic differences in the clinopyroxene mineralogy of the two suites seem also to be well established. The aim of this paper is to demonstrate that such generalization cannot be accepted, as natural conditions can be realized under which the fractionation of alkalic or mildly alkalic basalts may produce series with strong iron enrichment and with clinopyroxene mineralogy  atypical for basalts of alkaline affinity.In the Erta'Ale volcanic range (Northern Danakil Depression, Ethiopia), an example of such a serie is found, with a mildly alkalic basaltic magma fractionating under low and falling oxygen fugacity and giving rise to a series with some tholeiitic chemical and mineralogical features. |
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