gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/002646199548420 Petrogenesis of Plagioclase Phenocrysts of Mount Etna, Sicily, with Particular Reference to the 1983 Eruption: Contribution from Cathodoluminescence Petrography Stirling D. Duncan A. M. Centre for Volcanic Studies, University of Luton, Park Square, Luton LU1 3JU, UK Guest J. E. Planetary Image Centre, University College London, London NW7 4SD, UK Finch A. A. Dept. of Environmental Sciences, University of Hertfordshire, Hatfield AL10 9AB, UK 4 1999 63 2 189 198 11 5 1998 14 10 1998 Copyright © 1999, The Mineralogical Society 1999 Abstract

The cathodoluminescence (CL) characteristics of plagioclase phenocrysts in water-quenched lavas from the 1983 eruption of Etna have been investigated to examine the application of plagioclase CL to the study of magmatic processes. The phenocrysts have a green luminescent inner zone that is sharply bounded by a blue luminescent outer zone, with the boundary often coinciding with a concentric zone of glass inclusions.

Strong compositional differences between the green (An70-An75) and blue (An50-An60) luminescent areas are interpreted as the result of two phases of growth under differing conditions. The green luminescent cores are considered to be anorthite-rich cumulate crystals from a basic magma which have been disrupted by the injection of a more evolved melt, resulting in heterogeneous nucleation and crystallization of the outer blue luminescent zone. The relationship between the CL and the trace element contents of the plagioclase crystals is discussed.

 Keywords cathodoluminescence (CL) plagioclase Etna magmatic processes