Sector-zoned phlogopites in igneous rocks |
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Authors: | Christiane Wagner Danielle Velde Abdelkader Mokhtari |
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Affiliation: | (1) Laboratoire de Pétrologie Minéralogique, Université Pierre et Marie Curie and UA 0736 CNRS Tour 16, E3-4, place Jussieu, F-75252 Paris Cédex 05, France |
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Abstract: | Sector-zoned micas are described in three occurrences of igneous rocks. Basal sectors (001) and lateral sectors (010) are well defined. Analyses of probably isochronous growth points indicate that there are consistent chemical composition differences between the sectors, the (010) sector being richer in Si and poorer in Ti, Fe, Al and Ba relative to the (001) sector. Within each sector type Fe/ (Fe + Mg) increases from core to rim. These differences vary in amplitude from one occurrence to the other, but are systematic for micas with extremely different tetrahedral cations. Possible factors influencing this type of crystallization are briefly reviewed: growth rate, geometry of protosites and bulk composition of the liquid. |
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