Evaluating Magma Ascent Rates Beneath Central Andean Monogenetic Volcanoes

Authors: Mitchell P. Duncan, Claire L. McLeod, Liannie C. Velázquez Santana Faculty Mentor: Claire L. McLeod Department: Department of Geology and Environmental Earth Science Institution: Miami University Institution Address: 501 E High St, Oxford, OH 45056

Reaction rims surrounding amphiboles in hornblendites offer a unique opportunity to investigate the timescales associated with magma ascent. Furthermore, the hornblendites of this study were erupted from andesitic-dacitic lavas at the monogenetic Quillacas volcano in the Central Andes hence the reaction rim widths can also offer new insights into the magma dynamics beneath monogenetic centers at active continental margins. The hornblendites of this study were previously characterized for their mineralogy, textures, and geochemistry in Velázquez Santana et al. (2020). Briefly, the hornblendites consist of 90-95% amphibole, 5-10% plagioclase feldspar with the majority of the amphiboles exhibiting reaction rims. The rims were investigated using a Zeiss Supra 35 VP Scanning Electron Microscope (SEM) at the Center for Advanced Microscopy and Imaging (CAMI) at Miami University. The rims are gabbroic in nature and are composed of pyroxenes, plagioclase, and oxides. These reaction mineral products are a result of re-equilibration to new pressure and temperature conditions during ascent. From measuring 80 individual rim widths, the average width was 27.25μm (±26.71μm) with ~⅔ of measured rims 15-35μm in size. Using a 10μm bin size, 50% of the measured rims are 20-30μm in width, while using a 5μm bin size, 36% are 20-25μm in size. Using the average width of 27.25μm, and based on the experimental results of Rutherford and Hill (1993), ascent timescales of 5 to 15 days are inferred. Results from the rim width measurements will be compared to the rim widths of the amphiboles in the host andesitic-dacitic lavas. Based on the lavas’ amphiboles comparatively smaller size, it is likely these represent at least one additional amphibole crystal population in the magmatic system beneath the Quillacas center. Combined, this study will provide new insights into the timescales associated with magma ascent beneath monogenetic volcanoes in the Central Andes.

Additional Abstract Information

Presenter: Mitchell Duncan

Institution: Miami University

Type: Oral

Subject: Geography/Geology

Status: Approved

Time and Location

Session: Oral 4
Date/Time: Tue 11:00am-12:00pm
Session Number: 420
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