Details

Autor(en) / Beteiligte

• Malowany, K. S.
• Stix, J.
• de Moor, J. M.
• Chu, K.
• Lacrampe‐Couloume, G.
• Sherwood Lollar, B.

Titel

Carbon isotope systematics of T urrialba volcano, C osta R ica, using a portable cavity ring‐down spectrometer

Ist Teil von

• Geochemistry, geophysics, geosystems : G3, 2017-07, Vol.18 (7), p.2769-2784

Erscheinungsjahr

2017

Quelle

Wiley-Blackwell Full Collection

Beschreibungen/Notizen

• Abstract 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. Key Points Spatial heterogeneity in the δ 13 C of volcanic gases imply hydrothermal modification of volcanic CO 2 at Turrialba The hyperbolic mixing model for predicting volcanic end‐member compositions is preferred to the Keeling method Diurnal changes in δ 13 C can impact volcanic plume measurements in densely vegetated areas