Solidification front permeability and melt flow in synthetic and natural porous magmatic crystalline networks using a lattice-Boltzmann method
Abstract
Permeability remains the least well known parameter in estimating Darcy flow through a porous magmatic crystalline network. Here we study permeability using a lattice-Boltzmann (LB) method for grain-scale, single-phase, Darcian flow and demonstrate the evolution of melt flow patterns in natural and simulated samples. The LB model used is a three-dimensional implementation with 15 velocity directions and a bounce-back scheme to satisfy the no-slip boundary condition at solid surfaces. Flow was induced by imposing a horizontal pressure gradient, and permeability is calculated once a steady flow is achieved. Two independent pore structures are tested using the LB model. In the first, the texture is generated using a stochastic algorithm that simulates igneous texture development during progressive crystallization. This structure consists of connected polyhedra of varying size, position, and orientation in a three dimensional space. Simple kinetic models of nucleation and crystal growth used in the stochastic algorithm produce final igneous textures that are consistent with CSDs (Crystal Size Distributions) of natural rocks (Hersum and Marsh, 2003, EOS). The second pore structure tested is that obtained directly using X-ray CT (Computed Tomography) of a 50% melted natural sample from the Holyoke basalt flow (Philpotts et al. 1999, Am. Min.). The LB predicted permeability for the simulated textures deviates from the permeability calculated using the empirical Carmen-Kozeny relationship. We fit our results to a similar correlation model for permeability. The predicted melt flow pattern becomes increasingly channelized at a multiple grain scale with decreasing melt fraction. This localization of flow produces a fabric in the resulting texture that reflects both a physical and chemical approach to equilibrium. The ensuing rock thus is anisotropic in `reactiveness' and strength.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSM.V23E..06H
- Keywords:
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- 3640 Igneous petrology;
- 5114 Permeability and porosity;
- 8429 Lava rheology and morphology;
- 8434 Magma migration;
- 8439 Physics and chemistry of magma bodies