FLUORINE CONCENTRATION IN MAGMATIC MELTS: EVIDENCE FROM INCLUSIONS IN MINERALS

Abstract

The paper summarizes data on fluorine concentrations in magmatic silicate melts (833 analyses of fluorine and other major components from 69 publications). This data was obtained in studies of glasses from homogenous melt inclusions in minerals and chilled glasses from ocean-floor volcanic rocks. Two types of melts were distinguished for basic and ultrabasic magmas (SiO2 = 40-53 wt %): the first type contains less than 1.3% of K2O and the second type, more than 1.3%. The average concentration of fluorine in melts of the first type is 0.029 wt % (196 analyses) and 0.299 wt % (29 analyses) in melts of the second type. The concentration of fluorine is 0.143 wt % (62 analyses) in magmas of intermediate composition (third type, SiO2 = 53-64 wt %). Several melt types were distinguished for silicic magmas (SiO2 > 64 wt %): melts with ordinary composition (fourth type), melts enriched in chlorine and iron (fifth type, or pantellerite, comendite, and alkaline granite), and melts enriched in fluorine (sixth type, or topaz rhyolite, ongonite, Li-F granite, and pegmatite). The average concentration of fluorine in melts of the fourth type is 0.196 wt % (336 analyses), 0.273 wt % in melts of the fifth type (41 analyses), and 2.087 wt % in melts of the sixth type (169 analyses). Considering the various abundances of these rock types on continents and seafloor, the average concentration of fluorine in magmatic melts is estimated as 0.094 wt % for continental blocks and 0.052 wt % for continents, continental margins, and sea-floor.