The effect of effective rock viscosity on 2-D magmatic porosity waves
<p>In source regions of magmatic systems the temperature is above solidus, and melt ascent is assumed to occur predominantly by two-phase flow, which includes a fluid phase (melt) and a porous deformable matrix. Since McKenzie (1984) introduced equations for two-phase flow, numerous solutions...
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doaj-6e6413be2dc54dac96e5151c49a6507f2020-11-25T00:34:39ZengCopernicus PublicationsSolid Earth1869-95101869-95292019-12-01102103211310.5194/se-10-2103-2019The effect of effective rock viscosity on 2-D magmatic porosity wavesJ. DohmenH. SchmelingJ. P. Kruse<p>In source regions of magmatic systems the temperature is above solidus, and melt ascent is assumed to occur predominantly by two-phase flow, which includes a fluid phase (melt) and a porous deformable matrix. Since McKenzie (1984) introduced equations for two-phase flow, numerous solutions have been studied, one of which predicts the emergence of solitary porosity waves. By now most analytical and numerical solutions for these waves used strongly simplified models for the shear- and bulk viscosity of the matrix, significantly overestimating the viscosity or completely neglecting the porosity dependence of the bulk viscosity. Schmeling et al. (2012) suggested viscosity laws in which the viscosity decreases very rapidly for small melt fractions. They are incorporated into a 2-D finite difference mantle convection code with two-phase flow (FDCON) to study the ascent of solitary porosity waves. The models show that, starting with a Gaussian-shaped wave, they rapidly evolve into a solitary wave with similar shape and a certain amplitude. Despite the strongly weaker rheologies compared to previous viscosity laws, the effects on dispersion curves and wave shape are only moderate as long as the background porosity is fairly small. The models are still in good agreement with semi-analytic solutions which neglect the shear stress term in the melt segregation equation. However, for higher background porosities and wave amplitudes associated with a viscosity decrease of 50 % or more, the phase velocity and the width of the waves are significantly decreased. Our models show that melt ascent by solitary waves is still a viable mechanism even for more realistic matrix viscosities.</p>https://www.solid-earth.net/10/2103/2019/se-10-2103-2019.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
J. Dohmen H. Schmeling J. P. Kruse |
spellingShingle |
J. Dohmen H. Schmeling J. P. Kruse The effect of effective rock viscosity on 2-D magmatic porosity waves Solid Earth |
author_facet |
J. Dohmen H. Schmeling J. P. Kruse |
author_sort |
J. Dohmen |
title |
The effect of effective rock viscosity on 2-D magmatic porosity waves |
title_short |
The effect of effective rock viscosity on 2-D magmatic porosity waves |
title_full |
The effect of effective rock viscosity on 2-D magmatic porosity waves |
title_fullStr |
The effect of effective rock viscosity on 2-D magmatic porosity waves |
title_full_unstemmed |
The effect of effective rock viscosity on 2-D magmatic porosity waves |
title_sort |
effect of effective rock viscosity on 2-d magmatic porosity waves |
publisher |
Copernicus Publications |
series |
Solid Earth |
issn |
1869-9510 1869-9529 |
publishDate |
2019-12-01 |
description |
<p>In source regions of magmatic systems the temperature is
above solidus, and melt ascent is assumed to occur predominantly by two-phase
flow, which includes a fluid phase (melt) and a porous deformable matrix.
Since McKenzie (1984) introduced equations for two-phase flow, numerous
solutions have been studied, one of which predicts the emergence of solitary
porosity waves. By now most analytical and numerical solutions for these
waves used strongly simplified models for the shear- and bulk viscosity of
the matrix, significantly overestimating the viscosity or completely
neglecting the porosity dependence of the bulk viscosity. Schmeling et al. (2012) suggested viscosity laws in which the viscosity decreases very
rapidly for small melt fractions. They are incorporated into a 2-D finite
difference mantle convection code with two-phase flow (FDCON) to study the
ascent of solitary porosity waves. The models show that, starting with a
Gaussian-shaped wave, they rapidly evolve into a solitary wave with similar
shape and a certain amplitude. Despite the strongly weaker rheologies
compared to previous viscosity laws, the effects on dispersion curves and wave
shape are only moderate as long as the background porosity is fairly small.
The models are still in good agreement with semi-analytic solutions which
neglect the shear stress term in the melt segregation equation. However, for
higher background porosities and wave amplitudes associated with a viscosity
decrease of 50 % or more, the phase velocity and the width of the waves
are significantly decreased. Our models show that melt ascent by solitary
waves is still a viable mechanism even for more realistic matrix
viscosities.</p> |
url |
https://www.solid-earth.net/10/2103/2019/se-10-2103-2019.pdf |
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