An Experimental Study on the Role of Water Vapor in the Distribution of Fluorine and Chlorine in Volcanic Rocks

Abstract

Abstract Fluorine and chlorine contents of volcanic rocks were examined with respect to the characteristics of the rocks. Fluorine showed rather linear relationships with some chemical components of the rocks and also with stages in the differentiation of magmas. But any universal relationship covering all the rock types was not found. The cause of this fact is expected to be the loss of halogens from rocks resulted from the interaction between rocks and water vapor, which is believed to be ubiquitous in magma and is gradually emanated from it during or after the formation of rocks. So, in order to make clear the role of water vapor in the distribution of halogens in rocks, the author has distilled fluorine and chlorine from rock samples with water vapor at elevated temperatures and studied following relations; (1) the relationship between the amount of distilled halogens and the fluorine and chlorine contents of the rocks, and (2) the relationship between the amount of distilled halogens and the characteristics of the rocks. In distillation of fluorine and chlorine with water vapor, almost all fluorine remained in each rock specimen at low temperatures below 300°C, and at temperatures above 700°C the ratio of the amount of distilled fluorine to the initial amount of fluorine in rocks fluctuated among specimens. However, there was no relation between patterns of the distilled fluorine and the fluorine content of the rocks, and also the characteristics of the rocks. Meanwhile, distillation curve of chlorine showed various patterns without having any relation to chlorine content of the rocks, and indicated that chlorine was retained more in basic rocks than in acidic rocks at higher temperatures, although no relation was observed between the chlorine content of the rocks and the characteristics of the rocks. Generally the ratio of distilled fluorine to initial fluorine in rocks is smaller than the ratio of distilled chlorine to initial chlorine in rocks at low temperatures. The results of the distillation experiments suggest that the distillation process of halogens with water vapor controlls the distribution of halogens in volcanic rocks more than does the chemical and mineralogical nature of the rocks.