Details
| Original language | English |
|---|---|
| Article number | egr027 |
| Pages (from-to) | 1737-1762 |
| Number of pages | 26 |
| Journal | Journal of Petrology |
| Volume | 52 |
| Issue number | 9 |
| Publication status | Published - 4 Aug 2011 |
Abstract
Magma degassing processes are commonly elucidated by studies of melt inclusions in erupted phenocrysts and measurements of gas discharge at volcanic vents, allied to experimentally constrained models of volatile solubility. Here we develop an alternative experimental approach aimed at directly simulating decompression-driven, closed-system degassing of basaltic magma in equilibrium with an H-C-O-S-Cl fluid under oxidized conditions (fO2 of 1·0-2·4 log units above the Ni-NiO buffer). Synthetic experimental starting materials were based on basaltic magmas erupted at the persistently degassing volcanoes of Stromboli (Italy) and Masaya (Nicaragua) with an initial volatile inventory matched to the most undegassed melt inclusions from each volcano. Experiments were run at 25-400MPa under super-liquidus conditions (11508C). Run product glasses and starting materials were analysed by electron microprobe, secondary ion mass spectrometry, Fourier transform infrared spectroscopy, Karl-Fischer titration, Fe2+/Fe3+ colorimetry and CS analyser. The composition of the exsolved vapour in each run was determined by mass balance. Our results show that H2O/ CO2 ratios increase systematically with decreasing pressure, whereas CO2/S ratios attain a maximum at pressures of 100-300MPa. S is preferentially released over Cl at low pressures, leading to a sharp increase in vapour S/Cl ratios and a sharp drop in the S/Cl ratios of glasses. This accords with published measurements of volatile concentrations in melt inclusion and groundmass glasses at Stromboli (and Etna). Experiments with different S abundances show that the H2Oand CO2 contents of the melt at fluid saturation are not affected. The CO2 solubility in experiments using both sets of starting materials is well matched to calculated solubilities using published models. Models consistently overestimate H2O solubilities for the Stromboli-like composition, leading to calculated vapour compositions that are more CO2-rich and calculated degassing trajectories that are more strongly curved than observed in experiments. The difference is less acute for the Masaya-like composition, emphasizing the important compositional dependence of solubility and melt- vapour partitioning. Our novel experimental method can be readily extended to other bulk compositions.
Keywords
- Basalt, Degassing, Experiments, Masaya, Solubility, Stromboli
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geophysics
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
Cite this
- Standard
- Harvard
- Apa
- Vancouver
- BibTeX
- RIS
In: Journal of Petrology, Vol. 52, No. 9, egr027, 04.08.2011, p. 1737-1762.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Experimental simulation of closed-system degassing in the system basalt-H2O-CO2-S-Cl
AU - Lesne, Priscille
AU - Kohn, Simon C.
AU - Blundy, Jon
AU - Witham, Fred
AU - Botcharnikov, Roman E.
AU - Behrens, Harald
N1 - Funding Information: This research was supported by NERC standard grant NE/ F004222/1.
PY - 2011/8/4
Y1 - 2011/8/4
N2 - Magma degassing processes are commonly elucidated by studies of melt inclusions in erupted phenocrysts and measurements of gas discharge at volcanic vents, allied to experimentally constrained models of volatile solubility. Here we develop an alternative experimental approach aimed at directly simulating decompression-driven, closed-system degassing of basaltic magma in equilibrium with an H-C-O-S-Cl fluid under oxidized conditions (fO2 of 1·0-2·4 log units above the Ni-NiO buffer). Synthetic experimental starting materials were based on basaltic magmas erupted at the persistently degassing volcanoes of Stromboli (Italy) and Masaya (Nicaragua) with an initial volatile inventory matched to the most undegassed melt inclusions from each volcano. Experiments were run at 25-400MPa under super-liquidus conditions (11508C). Run product glasses and starting materials were analysed by electron microprobe, secondary ion mass spectrometry, Fourier transform infrared spectroscopy, Karl-Fischer titration, Fe2+/Fe3+ colorimetry and CS analyser. The composition of the exsolved vapour in each run was determined by mass balance. Our results show that H2O/ CO2 ratios increase systematically with decreasing pressure, whereas CO2/S ratios attain a maximum at pressures of 100-300MPa. S is preferentially released over Cl at low pressures, leading to a sharp increase in vapour S/Cl ratios and a sharp drop in the S/Cl ratios of glasses. This accords with published measurements of volatile concentrations in melt inclusion and groundmass glasses at Stromboli (and Etna). Experiments with different S abundances show that the H2Oand CO2 contents of the melt at fluid saturation are not affected. The CO2 solubility in experiments using both sets of starting materials is well matched to calculated solubilities using published models. Models consistently overestimate H2O solubilities for the Stromboli-like composition, leading to calculated vapour compositions that are more CO2-rich and calculated degassing trajectories that are more strongly curved than observed in experiments. The difference is less acute for the Masaya-like composition, emphasizing the important compositional dependence of solubility and melt- vapour partitioning. Our novel experimental method can be readily extended to other bulk compositions.
AB - Magma degassing processes are commonly elucidated by studies of melt inclusions in erupted phenocrysts and measurements of gas discharge at volcanic vents, allied to experimentally constrained models of volatile solubility. Here we develop an alternative experimental approach aimed at directly simulating decompression-driven, closed-system degassing of basaltic magma in equilibrium with an H-C-O-S-Cl fluid under oxidized conditions (fO2 of 1·0-2·4 log units above the Ni-NiO buffer). Synthetic experimental starting materials were based on basaltic magmas erupted at the persistently degassing volcanoes of Stromboli (Italy) and Masaya (Nicaragua) with an initial volatile inventory matched to the most undegassed melt inclusions from each volcano. Experiments were run at 25-400MPa under super-liquidus conditions (11508C). Run product glasses and starting materials were analysed by electron microprobe, secondary ion mass spectrometry, Fourier transform infrared spectroscopy, Karl-Fischer titration, Fe2+/Fe3+ colorimetry and CS analyser. The composition of the exsolved vapour in each run was determined by mass balance. Our results show that H2O/ CO2 ratios increase systematically with decreasing pressure, whereas CO2/S ratios attain a maximum at pressures of 100-300MPa. S is preferentially released over Cl at low pressures, leading to a sharp increase in vapour S/Cl ratios and a sharp drop in the S/Cl ratios of glasses. This accords with published measurements of volatile concentrations in melt inclusion and groundmass glasses at Stromboli (and Etna). Experiments with different S abundances show that the H2Oand CO2 contents of the melt at fluid saturation are not affected. The CO2 solubility in experiments using both sets of starting materials is well matched to calculated solubilities using published models. Models consistently overestimate H2O solubilities for the Stromboli-like composition, leading to calculated vapour compositions that are more CO2-rich and calculated degassing trajectories that are more strongly curved than observed in experiments. The difference is less acute for the Masaya-like composition, emphasizing the important compositional dependence of solubility and melt- vapour partitioning. Our novel experimental method can be readily extended to other bulk compositions.
KW - Basalt
KW - Degassing
KW - Experiments
KW - Masaya
KW - Solubility
KW - Stromboli
UR - http://www.scopus.com/inward/record.url?scp=80052213132&partnerID=8YFLogxK
U2 - 10.1093/petrology/egr027
DO - 10.1093/petrology/egr027
M3 - Article
AN - SCOPUS:80052213132
VL - 52
SP - 1737
EP - 1762
JO - Journal of Petrology
JF - Journal of Petrology
SN - 0022-3530
IS - 9
M1 - egr027
ER -