EXPERIMENTAL STUDY OF THE EFFECT OF OXYGEN FUGACITY ON LOW PRESSURE PHASE RELATIONS OF BASALTIC ANDESITE FROM THE ACATLÁN VOLCANIC FIELD, JALISCO, MEXICO

A wide variety of volcanic rocks have erupted at the Acatlan Volcanic Field, which is located southwest of Guadalajara, Mexico. This volcanic field is part of the Mexican Volcanic Belt, and it is situated very near a triple junction where three tectonic rifts converge. During the Quaternary, basaltic lava flows, andesite flows and cinder cones, and dacite and rhyolite domes were formed, along with a zoned ignimbrite that is rhyolitic at the base and andesitic at the top. In order to determine if a basaltic andesite from this area could be parental to the more evolved lavas erupted there, melting experiments were conducted on this composition at 1 atmosphere pressure. Experiments were conducted in a vertical tube, gas-mixing furnace. Oxygen fugacity was controlled using mixtures of hydrogen and carbon dioxide gases. Two sets of experiments were conducted under two oxygen fugacity conditions, one at the QFM buffer and the other at the Ni-NiO buffer.