The processes of alteration of volcanic rocks under the influence of the fumarolic gases in the Tatun Volcano Group, Taiwan

Abstract

The purpose of this study is to examine the processes of alteration under the influence of fumarolic gases by the comparison of variations in chemical compositions of the series of alteration products from several loci found in the Tatun Volcann Group (TVG), Taiwan. 26 rock samples are collected from Longenku and Liuhunagku, which are both active volcanic gas emission areas in the TVG, Taiwan. Samples are then analyzed by Scanning Electron Microscope, polarizing microscope, X-ray Diffractometer, Energy-dispersive X-ray spectroscopy and Energy Dispersive X-Ray Fluorescence to establish the linkage.The preliminary results show that there are wo types of the fumarolic alteration rocks were found in this study. Samples, taken away from fumaroles, consist of augite, hypersthene, hornblende and plagioclase with relative lower content of silica (up 54%) and no sulfur. On the other hand, samples, taken near fumaroles, consist of mainly opal, cristobalite and few plagioclases with relative higher content of silica (up to 90%) and sulfur elements. It suggests that volcanic gas such sulfur replaces magnesium and sodium in rock to make silica content increased in volume. This is the first report of this finding in TVG, Taiwan.