T239 Basaltic Volcanism on Earth and Beyond: Exploring the Physical Controls on Eruptive Styles and Associated Deposits

Wednesday, 25 September 2019
8:00 AM - 12:00 PM
Room 128AB, North Building

PARTIAL PRESSURES OF CRYSTALLIZATION AND OXYGEN FUGACITIES FOR THE JUAN DE FUCA RIDGE, VOLCAN DE FUEGO AND VOLCAN DE PACAYA (GUATEMALA): A COMPARATIVE STUDY OF THE DEPTHS OF MAGMA STORAGE AND REDOX CONDITIONS FOR MID-OCEAN RIDGES AND ARC VOLCANOES

Paper number: T239-6
Program: Technical Sessions
Time: 9:15 AM – 9:30 AM

Authors

Abstract

Basaltic volcanism occurs in a wide range of geologic settings and is associated with both flux melting and melting due to adiabatic decompression. In order to better understand the magma plumbing systems of mafic volcanic systems in various geologic settings, and to characterize the composition and redox conditions of the mantle sources of these mafic melts, we investigate the partial pressures of crystallization (PPCs) and oxygen fugacities (ƒO2) for basaltic glasses from the Juan de Fuca Ridge (JdFR), an intermediate-rate spreading ridge, and Fuego and Pacaya volcanoes (Guatemala), two highly-active arc volcanoes with basalts as their primary eruptive products. PPCs are determined using the geobarometer described by Kelley and Barton (2008), which quantitatively calculates pressures by comparing the compositions of mafic glasses to those of experimental glasses in equilibrium with olivine, plagioclase, and clinopyroxene at various pressures, as described by Yang et al. (1996). The Olivine-Melt Equilibrium method is used for ƒO2 calculations. This method was developed by Barton (2003), and uses equilibrium between olivine and glass in order to determine the melt Fe3+/Fe2+ ratio to calculate the ƒO2. It can therefore be applied to glass data for which the Fe3+/Fe2+ ratio has not been determined analytically.

Published glass data are used for these calculations for the JdFR, and a mixture of published glass data analyses of glass in new samples will be used for the calculations for Fuego and Pacaya. For the JdFR, our results show that there is a general decrease in pressure with increasing latitude. In addition, we have determined that virtually all crystallization occurs within the crust. There is no evidence for significant crystallization in the mantle as suggested by previous workers. The average ƒO2 for the JdFR is FMQ-1, which is similar to ƒO2 values determined at other MORs using the olivine-melt method. The samples from Fuego and Pacaya will allow for the direct comparison of the PPCs and ƒO2 for these volcanoes to those for the JdFR through the use of internally consistent methods.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-337888

© Copyright 2019 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.