Degassing of H2O in a phonolitic melt: A closer look at decompression experiments

Inclusion of Viscosity Into Classical Homogeneous Nucleation Theory for Water Bubbles in Silicate Melts: Reexamination of Bubble Number Density in Ascending Magmas

“…The light red lines indicate the prediction under an increasing decompression rate for P e =10 −3.75 (rhyolitic melt) and P e =10 −1.0 (andesitic melt). They seem to roughly correspond to the distributions of data found by Marxer et al () and Mourtada‐Bonnefoi and Laporte (). The slopes of the lines P e =10 −6.5 and P e =10 −3.75 are −1.37, and the slope of the line P e =10 −1.0 is −1.5.…”

“…Fiege and Cichy () made a list of experimental studies using continuous or nearly continuous decompression rates (see Table 1 in their paper). From the list, we extracted 10 homogeneous bubble nucleation experiments (Fiege et al, ; Gondé et al, ; Hamada et al, ; Mangan & Sisson, ; Martel & Bureau, ; Marxer et al, ; Mourtada‐Bonnefoi & Laporte, , , ; Pichavant et al, ) and calculated the viscosity parameter α 4 = P 0 t dec /4 μ for each. The model presented by Hui and Zhang () was adopted for the melt viscosity estimation.…”

“…Almost all data for the melt compositions were in the range of andesite to rhyolite, except for Pichavant et al (2013), which used a low-viscous basaltic melt. All experimental conditions are plotted in the diffusion-controlled regime, and differences of the BND values seem to be explained by differences in the diffusion parameter 3 (Fiege & Cichy, 2015;Gondé et al, 2011;Hamada et al, 2010;Marxer et al, 2015;Mangan & Sisson, 2000;Mourtada-Bonnefoi & Laporte, 2004). Light red lines in Figure 7 indicate the trends of the virtual experimental results under increasing decompression rates, when Pe = 10 −3.75 (rhyolitic melt) and Pe = 10 −1.0 (andesitic melt).…”

“…Since melt viscosity heavily depends on melt temperature, we next examined how decompression rates and temperatures control the boundary conditions between those regimes. Figure 8 shows the boundaries between the diffusion-controlled regime and the viscosity-controlled regime as functions of the decompression rate, |dP m ∕dt|, versus melt temperature, T, for the three patterns of melt compositions: the extreme composition melt proposed above (deep green), rhyolotic melt (green, the same composition as the one used in Mourtada-Bonnefoi & Laporte, 2004), and andesitic melt (yellowish green, the same composition as the one used in Marxer et al, 2015). The sets of initial water content and melt pressure, P 0 , for each composition are Figure 7).…”

Vesiculation in rhyolite at low H2O contents: A thermodynamic model

“…These studies have elucidated a diversity of competing processes and rates inherent in the vesiculation process. Experimental studies of bubble nucleation and growth dynamics in natural silicate melts have mainly relied on depressurization events of 10's to 100's of MPa applied to H 2 O oversaturated melts held at elevated pressures and temperatures [e.g., Hurwitz and Navon, 1994;Lyakhovsky et al, 1996;Gardner et al, 2000;Mangan and Sisson, 2000;Lensky et al, 2004;Mourtada-Bonnefoi and Laporte, 2004;Baker et al, 2006;Hamada et al, 2010;Gardner and Ketcham, 2011;Gonnermann and Gardner, 2013;McIntosh et al, 2014;Martel and Iacono-Marziano, 2015;Marxer et al 2015]. In these experiments, decompression rapidly moves the melt from undersaturated or saturated states to oversaturation, where bubble nucleation and growth operate far from chemical equilibrium.…”