Fluorite stability in silicic magmas |
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Authors: | Email author" target="_blank">B?ScailletEmail author R?Macdonald |
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Institution: | (1) Institut des Sciences de la Terre d Orléans, UMR 6113 CNRS-UO, 1A rue de la Férollerie, 45071 Orléans, France;(2) Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK |
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Abstract: | Recent experimental evidence is used to assess the conditions under which fluorite forms an early crystallising phase in silicic magmas. Fluorite solubility primarily depends on the (Na + K)/Al balance in the coexisting silicic melt, reaching a minimum in metaluminous melts. It can display reaction relationships with topaz and titanite, depending on changes in melt composition during crystallisation. An empirical model of fluorite stability in Ca-poor peralkaline rhyolite melts is derived and applied to selected rocks: At the F contents preserved in most silicic rocks, fluorite should normally appear late in the crystallisation sequence, in agreement with petrographic observations. During fluid-absent crustal anatexis, fluorite should melt at a relatively early stage and restitic fluorite is unlikely to persist during prolonged melting. Fluorite may, however, exert a decisive control on the alkali/alumina balance of sub-aluminous anatectic melts and it can affect the liquid line of descent of silicic magmas once extracted from source.Editorial responsibility: J. Hoefs |
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