Publication Date:
2019
Description:
Abstract
Studying spatial and temporal trends in volcanic gas compositions and fluxes is crucial to both volcano monitoring and to constrain the origin and recycling efficiency of volatiles at active convergent margins. New compositions and fluxes are here reported for Nevado del Ruiz, Galeras and Purace, the most persistently degassing volcanoes in the Colombian Arc Segment (CAS) of the Northern Volcanic Zone (NVZ). At Nevado del Ruiz, from 2014 to 2017, plume emissions showed an average molar CO2/ST ratio of 3.9 ± 1.6 (ST is total sulfur, S). Contemporary, fumarolic chemistry at Galeras progressively shifted towards low‐temperature, S‐depleted gas discharges with an average CO2/ST ratio in excess of 10 (6.0 – 46.0, 2014‐2017). This shift in volcanic gas compositions was accompanied by a concurrent decrease in SO2 emissions, confirmed on the 21 March 2017 by high‐resolution UV camera‐based SO2 fluxes of ~2.5 kg s‐1 (~213t d‐1). For comparison, SO2 emissions remained high at Nevado del Ruiz (weighted average of 8 kg s‐1) between 2014 and 2017, while Puracé maintained rather low emission levels (〈1 kg s‐1 of SO2, CO2/SO2 ≈ 14). We here estimate carbon dioxide fluxes for Nevado del Ruiz, Galeras and Puracé of ~23, 30 and 1 kg s‐1, respectively. These, combined with recent CO2 flux estimates for Nevado del Huila of ~10 kg s‐1 (~860 t d‐1), imply that this arc segment contributes about 50% to the total subaerial CO2 budget of the Andean Volcanic Belt. Furthermore, our work highlights the northward increase in carbon‐rich sediment input into the mantle wedge via slab fluids and melts that is reflected in magmatic CO2/ST values far higher than those reported for Southern Volcanic Zone (SVZ) and Central Volcanic Zone (CVZ) volcanoes. We estimate that about 20% (~1.3 Mt C/y) of the C being subducted (~6.19 Mt C/y) gets resurfaced through subaerial volcanic gas emissions in Colombia (Nevado del Ruiz ~0.7 Mt C/y). As global volcanic volatile fluxes continue to be quantified and refined, the contribution from this arc segment should not be underestimated.
Electronic ISSN:
1525-2027
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
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