Publication Date:
2017-07-01
Description:
Over the past two decades, activity at Turrialba volcano, Costa Rica, has shifted from hydrothermal to increasingly magmatic in character, with enhanced degassing and eruption potential. We have conducted a survey of the δ 13 C signatures of gases at Turrialba using a portable field-based CRDS with comparison to standard IRMS techniques. Our δ 13 C results of the volcanic plume, high-temperature vents, and soil gases reveal isotopic heterogeneity in the CO 2 gas composition at Turrialba prior to its recent phase of eruptive activity. The isotopic value of the regional fault system, Falla Ariete (–3.4 ± 0.1‰), is in distinct contrast with the Central crater gases (–3.9 ± 0.1‰) and the 2012 high-temperature vent (–4.4 ± 0.2‰), an indication that spatial variability in δ 13 C may be linked to hydrothermal transport of volcanic gases, heterogeneities in the source composition, or magmatic degassing. Isotopic values of CO 2 samples collected in the plume vary from δ 13 C of −5.2 to −10.0‰, indicative of mixing between atmospheric CO 2 (–9.2 ± 0.1‰), and a volcanic source. We compare the Keeling method to a traditional mixing model (hyperbolic mixing curve) to estimate the volcanic source composition at Turrialba from the plume measurements. The predicted source compositions from the Keeling and hyperbolic methods (–3.0 ± 0.5‰ and −3.9 ± 0.4‰, respectively) illustrate two potential interpretations of the volcanic source at Turrialba. As of the 29 October 2014, Turrialba has entered a new eruptive period, and continued monitoring of the summit gases for δ 13 C should be conducted to better understand the dominant processes controlling δ 13 C fractionation at Turrialba. © 2017. American Geophysical Union. All Rights Reserved.
Electronic ISSN:
1525-2027
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
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