Diffusive fractionation of H2O and CO2 during magma degassing

Yoshimura, Shumpei

doi:10.1016/j.chemgeo.2015.07.003

Cited by 15 publications

(19 citation statements)

References 56 publications

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“…In both studies, CO 2 concentration gradients were found in post-decompression glasses, either around gas bubbles or near the gas-melt interface. In contrast, no such diffusion profiles were identified for H 2 O, despite concentrations being lower (in most cases) than in pre-decompression glasses (Pichavant et al 2013;Yoshimura 2015;Le Gall et al 2015a; Le Gall and Pichavant 2016a, b). Pichavant et al (2013) suggested that two characteristic distances, the gas interface distance (either the distance between two bubbles in the melt or the distance to the gas-melt interface) and the volatile diffusion distance (a function of respective diffusivities of volatiles in the melt) control the degassing process.…”

Section: The Diffusive Fractionation Modelmentioning

confidence: 88%

“…1). Except in the very fast basalt decompression experiment of Yoshimura (2015), the anomalous behaviour of CO 2 is associated with significant H 2 O losses which results in post-decompression glasses plotting systematically left of theoretical equilibrium degassing trajectories in Fig. 1.…”

Section: Summary Of Experimental Evidencementioning

confidence: 94%

“…Both Pichavant et al (2013) and Yoshimura (2015) observed decoupling between the behaviour of H 2 O and CO 2 during experimental decompression and degassing. In both studies, CO 2 concentration gradients were found in post-decompression glasses, either around gas bubbles or near the gas-melt interface.…”

Section: The Diffusive Fractionation Modelmentioning

confidence: 96%

“…Pichavant et al (2013) suggested that two characteristic distances, the gas interface distance (either the distance between two bubbles in the melt or the distance to the gas-melt interface) and the volatile diffusion distance (a function of respective diffusivities of volatiles in the melt) control the degassing process. Yoshimura (2015) quantitatively formulated a diffusive fractionation model to describe the ascent and degassing of volatile-bearing magmas. The reader is referred to this work for details about the calculations.…”

Section: The Diffusive Fractionation Modelmentioning

confidence: 99%

See 3 more Smart Citations

Gases as Precursory Signals: Experimental Simulations, New Concepts and Models of Magma Degassing

Pichavant

Gall

Scaillet

2018

Advances in Volcanology

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Section: The Diffusive Fractionation Modelmentioning

confidence: 88%

Section: Summary Of Experimental Evidencementioning

confidence: 94%

Section: The Diffusive Fractionation Modelmentioning

confidence: 96%

Section: The Diffusive Fractionation Modelmentioning

confidence: 99%

See 2 more Smart Citations

Gases as Precursory Signals: Experimental Simulations, New Concepts and Models of Magma Degassing

Pichavant

Gall

Scaillet

2018

Advances in Volcanology

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“…The authors stressed the importance of two characteristic distances (the distance between bubbles and the volatile diffusion distance) in the control of the degassing process. This model attributes an important role to differences in diffusivities between the volatile components in the melt, as emphasized by Yoshimura (2015) who developed a diffusive fractionation model of H 2 O and CO 2 degassing. As an illustration, at P f = 50 MPa (D9#2), the calculated distance for CO 2 diffusion is only 150 µm in the time interval of the decompression experiment (Zhang and Ni, 2010) while the H 2 O diffusion is 1060 µm, i.e.…”

Section: Equilibrium Vs Non-equilibrium Degassingmentioning

confidence: 99%

Homogeneous bubble nucleation in H 2 O- and H 2 O-CO 2 -bearing basaltic melts: Results of high temperature decompression experiments

Gall

Pichavant

2016

Journal of Volcanology and Geothermal Research

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High pressure and temperature decompression experiments were conducted to provide experimental information on the conditions of homogeneous bubble nucleation in basaltic melts. Experiments were performed on H 2 O-and H 2 O-CO 2-bearing natural melts from Stromboli. Three starting volatile compositions were investigated: series #1 (4.91 wt.% H 2 O, no CO 2), series #2 (2.37-2.45 wt.% H 2 O, 901-1011 ppm CO 2) and series #3 (0.80-1.09 wt.% H 2 O, 840-923 ppm CO 2). The volatile-bearing glasses were first synthesized at 1200°C and 200 MPa, and second continuously decompressed in the pressure range 150-25 MPa and rapidly quenched. A fast decompression rate of 78 kPa/s (or 3 m/s) was applied to limit the water loss from the glass cylinder and the formation of a H 2 O-depleted rim. Postdecompression glasses were characterized texturally by X-ray microtomography. The results demonstrate that homogenous bubble nucleation requires supersaturation pressures (difference between saturation pressure and pressure at which homogeneous bubble nucleation is observed, ∆P HoN) ≤ 50-100 MPa. ∆P HoN varies with the dissolved CO 2 concentration, from << 50 MPa (no CO 2 , series #1) to ≤ 50 MPa (872 ± 45 ppm CO 2 , series #3) to < 100 MPa (973 ± 63 ppm CO 2 , series #2). In series #1 melts, homogeneous bubble nucleation occurs as two distinct events, the first at high pressure (200 < P < 150 MPa) and the second at low pressure (50 < P < 25 MPa), just below the fragmentation level. In contrast, homogenous nucleation in series #2 and #3 melts is a continuous process. As well, chemical near-equilibrium degassing occurs in the series #1 melts, unlike in the series #2 and #3 melts which retain high CO 2 concentrations even for higher vesicularities (up to 23% at 25 MPa). Thus, our experimental observations underline a significant effect of CO 2 on the physical mechanisms of bubble vesiculation in basaltic melts. Our experimental decompression textures either reproduce or approach the characteristics of explosive basaltic eruptions, in terms of vesicularity, bubble shapes, sizes and number densities. Unimodal, exponential to power law bubble size distributions were encountered and correlated with the different melt series, textural characteristics and types of degassing.

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Footprints and conditions of multistep alkali enrichment in basaltic melts at Piton de la Fournaise (La Réunion Island, Indian Ocean)

et al. 2021

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Deciphering magma evolution below ocean basaltic volcanoes is all the more challenging because magma mixing is a common process tending to modify the pristine geochemical diversity during magma ascent. On the western flank of the Piton de la Fournaise volcano, transitional basalts have compositions that testify to origins down to the upper mantle and display a widespread geochemical diversity ranging from a tholeiitic affinity to an alkaline one. There, we show that evolved melt inclusions and matrix glasses (MgO < 9 wt%) record an alkali enrichment coupled with a Ca/Al ratio decrease, which tracks the effect of clinopyroxene crystallization at the depth of the mantle-crust underplating layer. At this depth and shallower, reverse zoning of olivine crystals, clinopyroxene dissolution, and hybrid melt compositions testify to extensive mixing processes leading to a homogenization of the pristine geochemical footprint of melts upon ascent. Enrichment in incompatible trace elements in some evolved melt inclusions suggests that magma ponding at the depth of the mantle-crust underplating layer favours also assimilation of melts originating from low degrees of partial melting of cumulates (wehrlites, dunites). Conversely, the most primitive melt inclusions documented so far at La Réunion Island (MgO up to 11.2 wt%) better preserve a pristine geochemical variability related to partial melting of a slightly heterogeneous mantle source. We suggest that these slightly distinct source components may mirror the compositions of recent melts from the two closely located Piton de la Fournaise and Piton des Neiges volcanoes.

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Diffusive fractionation of H2O and CO2 during magma degassing

Cited by 15 publications

References 56 publications

Gases as Precursory Signals: Experimental Simulations, New Concepts and Models of Magma Degassing

Gases as Precursory Signals: Experimental Simulations, New Concepts and Models of Magma Degassing

Homogeneous bubble nucleation in H 2 O- and H 2 O-CO 2 -bearing basaltic melts: Results of high temperature decompression experiments

Footprints and conditions of multistep alkali enrichment in basaltic melts at Piton de la Fournaise (La Réunion Island, Indian Ocean)

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