Textural study of quartz crystals from explosive El Cajete sequence (~74 ka), Valles Caldera, New Mexico
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Authors
McCullough, Caleb
Thompson, Matthew
Kim, Jisoo
Issue Date
2025-04-25
Type
Other
Language
en_US
Keywords
Scholarship Sewanee 2025 , University of the South, volcanology,melt inclusions, quartz, cathodoluminescence, geology, Valles Caldera, explosive volcanism,
magmatic volatiles
Alternative Title
Abstract
A melt inclusion is a small droplet of magma enclosed within a growing crystal—typically quartz, olivine, or feldspar—in a volcanic system. It captures the magma’s composition at the moment it was trapped, including volatile elements like water and CO₂ that are usually lost during eruption. The purpose of this research is to analyze the melt inclusions of crystals found in the El Cajete, the youngest explosive eruption sequence in the Valles Caldera located in the Jemez Mountains in northern New Mexico. We hypothesize that the El Cajete sequence shows increasing explosivity and eruption complexity from lower to upper (older to younger) layers. While quartz crystal textures vary, changes in explosivity are more influenced by shallow conduit processes than deeper magmatic ones. In order to test this hypothesis, we analyzed different subsequences of the El Cajete, specifically the upper and lower eruptions. In this study, we looked at photos of loose quartz crystals from the eruptions and identified the number of melt inclusions, how structured each inclusion was, and many other criteria. It was found that the lower layers have an average of 5.8 melt inclusions per crystal while the upper layers have 9.3 per crystal. Only 39% of lower layer crystals have resorption textures indicating thermal disequilibrium, while 71% of upper layer crystals had these textures. Our findings are important because they provide a glimpse into chamber and conduit conditions and magma content at the time of eruption. The differences in crystals of the upper and lower sequences provides evidence of an evolving magmatic system over relatively short periods of time.
Description
Citation
Publisher
University of the South