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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Main Authors: J. Dohmen, H. Schmeling, J. P. Kruse
Format: Article
Language:English
Published: Copernicus Publications 2019-12-01
Series:Solid Earth
Online Access:https://www.solid-earth.net/10/2103/2019/se-10-2103-2019.pdf
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spelling 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&thinsp;% 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&thinsp;% 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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