COMPLEX ZONING IN VESUVIANITE FROM THE CANIGOU MASSIF, PYRENEES, FRANCE

Vesuvianite grains in a calc-silicate layer from the Canigou massif (P yrenees, France) display oscillatory concentric birefringence-zoning a nd a locally developed, discordant, nearly isotropic marginal zone. Th e boundaries between the zones correspond to sharp changes in the abun dance of Ti, Al, Mg and Fe, although only Ti displays a consistent pos itive correlation with birefringence. Systematic variation in cation a bundances also occurs within individual zones of equal birefringence, indicating that compositional zoning is, to some extent, independent o f birefringence. Several schemes of cation substitution appear to have been operative in the vesuvianite, and different substitutions seem t o have dominated at different times. The dominant substitutions in the higher-birefringence zones seem to be Ti + Mg reversible arrow 2Al an d Fe3+ reversible arrow Al, whereas Mg reversible arrow Fe2+ may occur in addition to Ti + Mg reversible arrow 2Al in the lower-birefringenc e zones.