Behavoir of Volatile Components in Magma and Magma Ascent and Eruption Processes Based on Melt Inclusion Analyses

Abstract

Volatile content in magma is one of the important controlling factors of magma ascent and volcanic eruptions. Melt inclusion analysis is a powerful method to estimate volatile concentration of pre-eruptive magma in a magma chamber. In the past 10-15 years, improvements in techniques for analysis of melt inclusions have advanced, and now melt inclusions are increasingly used as a volcanological tool to unravel magmatic processes. Important information on magma ascent and eruption processes obtained by melt inclusion analysis is (1) magma degassing and evolution processes and gas saturation pressure, (2) density of magma, (3) bubble volume in a magma chamber and (4) volume of degassed magma. Melt inclusion analyses applied to basaltic to rhyolitic eruptions reveal various behavior of volatile components in magma plumbing system; bubble formation in a upper part of a chamber due to fractional crystallization, volatile exsolution with pressure decrease, supply of volatile material from deeper magma to a upper magma chamber, accumulation of bubbles in a shallow magma chamber, and degassing of a magma chamber by magma convection in a conduit. Comparison of these results with geological and geophysical observation on structure of crust beneath volcanoes enable us to model magma plumbing system and magma ascent and eruption processes.