COMPOSITIONAL ANALYSIS OF OLIVINE-HOSTED MELT INCLUSIONS FROM PACAYA VOLCANO, GUATEMALA
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Date
2025-05
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The Ohio State University
Abstract
Vulcán Pacaya is a basaltic stratovolcano approximately 30km SSW of Guatemala City, Guatemala. Current subsurface processes at Pacaya are not well understood, with little published work in the area and sparse monitoring equipment. By studying the petrology and geochemistry of erupted materials from Vulcán Pacaya, we can better understand subsurface processes and triggers involved in eruptive activity. Tephra samples from 2006, 2010, 2014, 2019 and 2021 collected from various locations surrounding Pacaya volcano were selected for study. Olivine phenocrysts and olivine-hosted melt inclusions analyzed for major elements along transects, in crystal cores, and rims. Olivine compositions show most crystals are normally zoned, with some reverse zoning in 2006 and 2021 eruption samples. Average forsterite compositions show a total range from Fo66 to Fo72 for the eruptions. In 2006, core Fo compositions range from Fo63 to Fo75 within the same thin section, and from Fo65 to Fo71 in 2021. Core compositions in 2014 have a smaller range of Fo74 to Fo76, and core compositions in 2019 range between Fo63 and Fo66 in several thin sections. This larger range of Fo compositions in 2006 and 2021, in addition to crystals with reverse and normal zoning in the same sample, suggest magma mixing just prior to or during the eruptions in these years. Average Fo mol.% has steadily decreased from Fo75 in 1974 to Fo67 in 2021, which indicates increased cooling and magma differentiation over time. Therefore, magma mixing and differentiation may be important eruptive factors at Pacaya.