Mineral chemistry and petrogenetic aspects of the Vico lavas,Roman volcanic region,Italy |
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Authors: | A Cundari |
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Institution: | 1. School of Geology, University of Melbourne, 3052, Parkville, Victoria, Australia
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Abstract: | A detailed study of the phase chemistry of selected lavas from Vico shows that the “excess silica” in leucite is a significant and widespread crystal-chemical characteristic which may be interpreted in terms of an extended solubility of KAlSi3O8 and/or differential loss of potassium from the leucite structure. Plagioclase geothermometer data suggest increasing plagioclase control in the differentiation with decreasing Mg/Mg+Fe2+ ratios for the bulk rocks. The pyroxene compositions show moderate amounts of ferri-Tschermak's and Ca-Tschermak's molecules, probably controlled by temperature and compositional variations in the cooling liquids. Both microphenocrystal and late-crystallizing micas correspond to phlogopite compositions throughout the suite. The phase chemistry is discussed in relation to the differentiation of the suite and current petrogenetic models. |
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