Understanding degassing of mafic magmas is important for modeling eruptions and examining controls on eruption style. We conducted high-pressure-high-temperature isothermal decompression experiments to investigate the effects of decompression-induced crystallization on permeability development and magma degassing. Experiments were performed on hydrous basaltic andesite (54 wt% SiO2) decompression rates equivalent to magma ascent velocities of ~1-3 m s-1. We measured the gas flux of the quenched samples using a bench-top permeameter and calculated the Darcian (k1) and inertial (k2) permeabilities using the Forchheimer equation. The experimental samples developed permeability at a critical vesicularity (Φc) of 56.4 ± 2.7 vol% (at 0.125 MPa s-1) and 50.76 ± 5.6 vol% (at 0.083 MPa s-1), considerably lower than the Φc > 63 vol% permeability threshold determined for crystal-free basaltic andesite melts. The percolation threshold decrease is observed when the microlites comprise ≥~20 vol% and can be explained by the onset of yield strength, which occurs when the crystals form a loosely packed, touching framework. © 2017 Geological Society of America.
Bibliographical noteExport Date: 13 September 2017
Funding details: EAR-1145194, NSF, National Science Foundation
Funding details: University of Texas at Austin
Funding text: This work was funded by National Science Foundation grant EAR-1145194 (to Larsen) and by the AXA Research Fund and a Royal Society Research Merit Award (to Cashman). We thank Olivier Bachmann and two anonymous reviewers for comments and suggestions that greatly improved this manuscript. We gratefully acknowledge Owen Neill for building the bench-top permeameter, and Shingo Takeuchi for allowing us to use two samples as permeameter standards. We also thank the University of Alaska Fairbanks Advanced Instrumentation Laboratory for their analytical capabilities and the University of Texas at Austin for performing the X-ray computed tomography.
References: Delaney, G.W., Hilton, J.E., Cleary, P.W., Defining random loose packing for nonspherical grains (2011) Physical Review E: Statistical, Nonlinear, and Soft Matter Physics, 83; Giordano, D., Russell, J.K., Dingwell, D.B., Viscosity of magmatic liquids (2008) A model: Earth and Planetary Science Letters, 271, pp. 123-134; Hammer, J.E., Rutherford, M.J., An experimental study of the kinetics of decompressioninduced crystallization in silicic melt (2002) Journal of Geophysical Research, 107 (B1); Hoover, S.R., Cashman, K.V., Manga, M., The yield strength of subliquidus basalts-Experimental results (2001) Journal of Volcanology and Geothermal Research, 107, pp. 1-18; Kerr, R.C., Lister, J.R., The effects of shape on crystal settling and on the rheology of magmas (1991) Journal of Geology, 99, pp. 457-467; Klug, C., Cashman, K.V., Bacon, C.R., Structure and physical characteristics of pumice from the climactic eruption of Mount Mazama (Crater Lake), Oregon (2002) Bulletin of Volcanology, 64, pp. 486-501; Lindoo, A., Larsen, J.F., Cashman, K.V., Dunn, A.L., Neill, O.K., An experimental study of permeability development as a function of crystal-free melt viscosity (2016) Earth and Planetary Science Letters, 435, pp. 45-54; Mader, H.M., Llewellin, E.W., Mueller, S.P., The rheology of two-phase magmas (2013) A review and analysis: Journal of Volcanology and Geothermal Research, 257, pp. 135-158; Marxer, H., Bellucci, P., Nowak, M., Degassing of H2O in a phonolitic melt (2015) A closer look at decompression experiments: Journal of Volcanology and Geothermal Research, 297, pp. 109-124; Moore, G., Vennemann, T., Carmichael, I.S.E., An empirical model for the solubility of H2O in magmas to 3 kilobars (1998) American Mineralogist, 83, pp. 36-42; Morgan, D.J., Jerram, D.A., On estimating crystal shape for crystal size distribution analysis (2006) Journal of Volcanology and Geothermal Research, 154, pp. 1-7; Mueller, S., Scheu, B., Spieler, O., Dingwell, D.B., Permeability control on magma fragmentation (2008) Geology, 36, pp. 399-402; Mueller, S., Llewellin, E.W., Mader, H.M., The rheology of suspensions of solid particles (2009) Royal Society of London Proceedings, ser. A, 466, pp. 1201-1228; Mueller, S., Llewellin, E.W., Mader, H.M., The effect of particle shape on suspension viscosity and implications for magmatic flows (2011) Geophysical Research Letters, 38; Okumura, S., Nakamura, M., Takeuchi, S., Tsuchiyama, A., Nakano, T., Uesugi, K., Magma deformation may induce non-explosive volcanism via degassing through bubble networks (2009) Earth and Planetary Science Letters, 281, pp. 267-274; Oppenheimer, J., Rust, A.C., Cashman, K.V., Sandnes, B., Gas migration regimes and outgassing in particle-rich suspensions (2015) Frontiers in Physics, 3, pp. 1-13; Parmigiani, A., Huber, C., Bachmann, O., Chopard, B., Pore-scale mass and reactant transport in multiphase porous media flows (2011) Journal of Fluid Mechanics, 686, pp. 40-76; Parmigiani, A., Faroughi, S., Huber, C., Bachmann, O., Su, Y., Bubble accumulation and its role in the evolution of magma reservoirs in the upper crust (2016) Nature, 532, pp. 492-495; Philpotts, A.R., Nature of a flood-basalt-magma reservoir based on the compositional variation in a single flood-basalt flow and its feeder dike in the Mesozoic Hartford Basin, Connecticut (1998) Contributions to Mineralogy and Petrology, 133, pp. 69-82; Picard, D., Arbaret, L., Pichavant, M., Champallier, R., Launeau, P., The rheological transition in plagioclase-bearing magmas (2013) Journal of Geophysical Research, 118, pp. 1363-1377; Rader, E.L., (2010) Mineral stability in H2O undersaturated magmas, p. 91. , Experiments on basaltic andesite from Westdahl Volcano [M.S. thesis]: Fairbanks, University of Alaska Fairbanks; Rader, E.L., Larsen, J.F., Experimental phase relations of a low MgO Aleutian basaltic andesite at XH2O= 0.7-1 (2013) Contributions to Mineralogy and Petrology, 166, pp. 1593-1611; Rust, A.C., Cashman, K.V., Permeability of vesicular silicic magma (2004) Inertial and hysteresis effects: Earth and Planetary Science Letters, 228, pp. 93-107; Rust, A.C., Cashman, K.V., Permeability controls on expansion and size distributions of pyroclasts (2011) Journal of Geophysical Research, 116; Saar, M.O., Manga, M., Cashman, K.V., Fremouw, S., Numerical models of the onset of yield strength in crystal-melt suspensions (2001) Earth and Planetary Science Letters, 187, pp. 367-379; Spina, L., Cimarelli, C., Scheu, B., Di Genova, D., Dingwell, D.B., On the slow decompressive response of volatile-and crystal-bearing magmas (2016) An analogue experimental investigation: Earth and Planetary Science Letters, 433, pp. 44-53; Takeuchi, S., Nakashima, S., Tomiya, A., Permeability measurements of natural and experimental volcanic materials with a simple permeameter (2008) Toward an understanding of magmatic degassing processes: Journal of Volcanology and Geothermal Research, 177, pp. 329-339; Takeuchi, S., Tomiya, A., Shinohara, H., Degassing conditions for permeable silicic magmas (2009) Implications from decompression experiments with constant rates: Earth and Planetary Science Letters, 283, pp. 101-110; Walsh, S.D., Saar, M.O., Magma yield stress and permeability (2008) Insights from multiphase percolation theory: Journal of Volcanology and Geothermal Research, 177, pp. 1011-1019; Wright, H.M., Cashman, K.V., Gottesfeld, E.H., Roberts, J.J., Pore structure of volcanic clasts measurements of permeability and electrical conductivity (2009) Earth and Planetary Science Letters, 280, pp. 93-104
- High pressure effects
- Basaltic andesite
- Decompression rate
- Forchheimer equation
- High pressure high temperature
- Induced crystallization
- Isothermal decompression
- Magma degassing
- Percolation thresholds