Abstract
The chlorine in the samples from an outcrop of simple cooling unit of the Aso-III A pyroclastic flow deposit was determined as a mean of studying the behavior of chlorine during the cooling process of pyroclastic flow. Content of the insoluble chlorine only is discussed in this paper, since the water-solubule chlorine in rocks may not be magmatic in origin but have come from by contamination after cooling. The results obtained can be summarized as follows : 1. The insoluble chlorine content of the glassy phases in the Aso-II, Aso-III A and Aso-III B pyroclastic flow deposits ranges from 0.06 to 0.08% Cl. 2. The chlorine content in a simple cooling unit depends on crystallinity of the matrix of rocks, and glassy rocks contain higher amounts of chlorine than rocks of crystalline matrix. 3. The chlorine was expelled from melts as minerals crystallized out, and then, escaped to the air through secondary fumaroles, or other interspaces in the deposit. 4. The chlorine content of the fresh glassy rock, not hydrated, may give the most reliable information on the chlorine content of magma.
