75-33 Tiny bubbles, giant secrets: Revealing magma storage depths through fluid inclusions from Taʻū volcano, American Samoa

Session: Mineralogy, Geochemistry, Petrology, and Volcanology Student Session (Posters)

Poster Booth No.: 326

Presenting Author:

Isabelle Susman

Authors:

Susman, Isabelle¹, Wieser, Penny E.², Kattemalavadi, Amartya³, Downs, Drew T.⁴, DeVitre, Charlotte L.⁵, Deligne, Natalia I.⁶

(1) Department of Earth and Planetary Science, University of California, Berkeley, Berkeley, CA, USA, (2) Department of Earth and Planetary Science,, University of California, Berkeley, Berkeley, CA, USA, (3) Department of Earth and Planetary Science,, University of California, Berkeley, Berkeley, CA, USA, (4) U.S. Geological Survey, Hawaiian Volcano Observatory, Hilo, HI, USA, Hilo, HI, USA, (5) Department of Earth and Planetary Science, University of California, Berkeley, CA, USA; Department of Earth and Environmental Sciences, University of Ottawa, Ottowa, ON, Canada, (6) Hawaiian Volcano Observatory, US Geological Survey, Hilo, HI, Tunisia,

Abstract:

Taʻū Island, located in American Samoa, sits above a hotspot volcano that likely erupted in the Holocene. An earthquake swarm in 2022 highlighted the lack of geophysical monitoring at the time, as well as the lack of understanding into the plumbing system of this volcano, making the source of seismic activity difficult to diagnose as volcanic or not. To constrain the depth of the magmatic plumbing system, we analyzed pockets of exsolved fluid trapped within olivine crystals (fluid inclusions, FI) in dunite xenoliths from the Faleāsao tuff cone, Ta’ū. The density of CO₂ in a FI can be measured by Raman spectroscopy, and converted into a pressure (and thus entrapment depth) using the CO₂ equation of state and an estimate of the entrapment temperature. Initial FI analyses reveal highly varied densities within individual crystals (0.1–0.5 g/cm³), yielding storage depths spanning 1–8 km. We hypothesize that this variation stems from the sequestration of CO₂ as carbonate onto the walls of FIs, identified by a peak at 1090 cm^-1 in Raman spectra. While not all spectra exhibit this peak when analyzed at the center of the FI, carbonate is apparent in 2D Raman mapping. We heated crystals in O₂-stripped Ar gas up to 1150°C for 3 minutes using a Linkam stage, causing the carbonate to break down into CO₂ (see DeVitre et al. 2023). Post-heating Raman analysis reveals a much narrower density range of ~0.4–0.6 g/cm³. The CO₂ densities in 3 individual FI measured before and after heating increase from ~0.35–0.4 to 0.55–0.6 g/cm³. These results show that carbonate, even when not present in individual spectra, can result in an underestimation of FI densities. Preliminary chemical data shows a narrow range of olivine compositions (Fo_86–87, [Mg/(Mg+Fe2⁺)] molar%) within each xenolith, but with several Fo unit variations between xenoliths, indicative of storage of separate cumulate bodies. Additional FI barometry on heated samples will allow us to quantify the effects of carbonate on FI densities, as well as further explore the geometry of Ta’ū’s magmatic system. Overall, this research will allow us to place preliminary pressure and depth constraints on Taʻū volcano’s plumbing system, while also providing the community with a workflow to reliably obtain FI pressures from carbonate-rich samples. 

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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