CHLORINE AND FLUORINE IN THOLEIITIC AND ALKALINE LAVAS OF ETNA (SICILY)

Chlorine and fluorine were measured from whole-rock samples from tholeiites (150,000 years old) to present-day hawaiites. The overall range of F content is from 240 to 985 ppm, with a slight decrease of F/Th and F/Cl ratios, from tholeiites to hawaiites. Chlorine is positively correlated with Th (Cl/Th=100) as well as K2O and P2O5, as the differentiation progresses, and, increases from 220 ppm in tholeiites to 2410 ppm in mugearites. Data obtained from present-day hawaiites indicate that Cl lost by degassing during eruption is limited. However, Cl contents of some whole-rock samples are inconsistent with previous results published for melt inclusions of phenocrysts from the same historic hawaiite samples and suggesting outgassing of Cl prior to the eruption. This implies that apparent correlation between Cl and Th can be considered as the result of superimposition of several petrogenetic processes. Results point out the richness of Etnean tholeiites in chlorine compared to M.A.R. basalts. Such a character could have been inherited from the mantle source or during the mantle source melting. © 1990.