Progressive drying of the hydrothermal system of La Soufrière de Guadeloupe (French West Indies) revealed by multi-year monitoring of chlorine isotopic composition of fumarolic HCl

IF 2.4 3区地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY

Journal of Volcanology and Geothermal Research Pub Date : 2025-02-26 DOI:10.1016/j.jvolgeores.2025.108306

Étienne Le Glas , Magali Bonifacie , Roberto Moretti , Vincent Robert , Pierre Agrinier , Jabrane Labidi , Gérard Bardoux , Laëtitia Pantobe , Arnaud Burtin , Élodie Chillin-Eusebe , Tristan Didier , Manuel Inostroza

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引用次数: 0

Abstract

Closed-conduit volcanoes develop hydrothermal aquifers where infiltrating waters dissolve magmatic gases such as SO₂, HCl, and HF. The extent of this “scrubbing effect” is traditionally tracked using CO₂/SO₂ or CO₂/S_Total, but these ratios can also be modified by secondary processes. Given the high solubility of gaseous HCl_(g) into aqueous water, we assess here chlorine isotopic compositions (δ³⁷Cl) in fumarolic HCl_(g) as a potential quantitative index of scrubbing.

We present three years and a half (January 2018 to May 2021) of δ³⁷Cl and chlorine concentrations [Cl] data from fumarolic gases at La Soufrière de Guadeloupe, alongside traditional geochemical tracers in volcanology. Our data show strong negative correlation between δ³⁷Cl and [Cl] values, suggesting variable extents of HCl dissolution into the hydrothermal aquifer through time. High δ³⁷Cl values associated to low [Cl] indicate intense ³⁵Cl loss into the aquifer, while low δ³⁷Cl values with high [Cl] likely reflect more pristine magmatic signatures with minimal extents of scrubbing.

The observed δ³⁷Cl–[Cl] trends suggest Cl isotopic fractionation factors between gas and liquid Δ_g-l varying between +2.5 and +5 ‰. These values are higher than expected at equilibrium, suggesting kinetic fractionations likely resulting from rapid gas flow (preventing isotopic equilibration with liquid water). The fact that comparable δ³⁷Cl–[Cl] trends are found at Poás (Costa Rica) and Vulcano (Italy) suggests that such kinetic fractionations during HCl scrubbing may be widespread.

Comparisons between δ³⁷Cl and CO₂/CH₄ ratios and the modeled groundwater level within the dome suggest that variations in scrubbing at La Soufrière are primarily driven by varying magmatic inputs. The progressive decrease in δ³⁷Cl, associated with increasing [Cl] from 2019 to 2021, likely reflects long-term aquifer drying, predating the observed rise in fumarolic temperatures above 150 °C in mid-2023.

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来源期刊

Journal of Volcanology and Geothermal Research 地学-地球科学综合

CiteScore

5.90

自引率

13.80%

发文量

183

审稿时长

19.7 weeks

期刊介绍： An international research journal with focus on volcanic and geothermal processes and their impact on the environment and society. Submission of papers covering the following aspects of volcanology and geothermal research are encouraged: (1) Geological aspects of volcanic systems: volcano stratigraphy, structure and tectonic influence; eruptive history; evolution of volcanic landforms; eruption style and progress; dispersal patterns of lava and ash; analysis of real-time eruption observations. (2) Geochemical and petrological aspects of volcanic rocks: magma genesis and evolution; crystallization; volatile compositions, solubility, and degassing; volcanic petrography and textural analysis. (3) Hydrology, geochemistry and measurement of volcanic and hydrothermal fluids: volcanic gas emissions; fumaroles and springs; crater lakes; hydrothermal mineralization. (4) Geophysical aspects of volcanic systems: physical properties of volcanic rocks and magmas; heat flow studies; volcano seismology, geodesy and remote sensing. (5) Computational modeling and experimental simulation of magmatic and hydrothermal processes: eruption dynamics; magma transport and storage; plume dynamics and ash dispersal; lava flow dynamics; hydrothermal fluid flow; thermodynamics of aqueous fluids and melts. (6) Volcano hazard and risk research: hazard zonation methodology, development of forecasting tools; assessment techniques for vulnerability and impact.