The Role of Fluids in Crustal Processes (1990) / Chapter Skim
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1. Mass and Energy Transport in a Deforming Earth's Crust
1. Mass and Energy Transport in a Deforming Earth's Crust
Pages 27-41
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From page 27... ...
The same convective process also redistributes chemical components from the host to the pluton environments, including the ore-forming constituents. Therefore, groundwater flow controls the distribution and grade of many ore deposits.
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From page 28... ...
The symbolic formalism of mass and energy transport is used in an attempt to sketch a coherent picture of processes and to show the usefulness of the equations in revealing the role of the fluid phase in mass and energy transport within a deformable medium. The equations presented below are not original, so the reader is encouraged to explore in greater depth the transport theories such as those used in engineering (e.g., Bird et al., 1960; Slattery, 1972)
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From page 29... ...
flow through the pores, and at the macroscopic level, where heterogeneities in geologic materials greatly increase the magnitude of the dispersive process. Diffusion laterally away from the flow channels into fracture-controlled matrix blocks was recognized early in the study of hydrothermal ore deposits as the mechanism by which alteration haloes and high assays form in the rock matrix adjacent to fossil flow channels called veins.
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From page 30... ...
Although this set of partial differential equations the flow equations for pressure and the advection-dispersion equations for chemical solutes and energy, along with Darcy's Law form a complete conservation statement, the effects of stress and strain must also be considered. Stress and Strain In the 1920s, in investigating consolidation, Terzaghi treated soils as a water saturated porous mediums.
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From page 31... ...
When D is negative, the inelastic volume change acts to increase porosity with increasing shear stress. Mineral-Fluid Reactions The advection of chemical components by fluid flow and dispersive fluxes from one chemical environment to another causes chemical reactions between the minerals and fluids.
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From page 32... ...
(1970, 1979~. Once the rigorous description of mass transfer in systems that are only locally in equilibrium was placed on a thermodynamic basis, the rate of the irreversible reactions could be incorporated into the theory (Aagaard and Helgeson, 1982~.
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From page 33... ...
Field evidence and theoretical relations indicate that permeabilities in excess of 1~4 cm2 are common in magma environments (Taylor, 1974, 1977; Norton and Taylor, 1979~. The measured mass transfer of chemical components in ore deposits, layered intrusions, and batholiths requires that advection was a dominant process.
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From page 34... ...
Toth (1963) pointed out that the water table is the upper boundary for saturated groundwater flow and that this boundary is usually closely approximated by the land surface.
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From page 35... ...
The total difference in elevation forms a constraint on the hydraulic gradient. Under conditions in which elevation differences are the driving force for the groundwater flow system, the total drive on the system is limited by the available topographic relief.
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From page 36... ...
In their model crustal porosity, permeability, and hence fluid pressures are in general time dependent due to the gradual closure of crustal pore space via heating, sealing, and inelastic deformation. Under certain circumstances this process will lead to local drying out of the crust.
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From page 37... ...
The magnitude of the change in pore pressure induced by such changes is a function of the relative rate of change with respect to the rate at which groundwater flow dissipates the pressure increases. The rate of flow, in turn, depends on the permeability of the material.
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From page 38... ...
Convection cells are set up in the groundwater flow around the intrusive body. Of interest is how the convecting groundwater might redistribute metals and ore-forming fluids emanating from the igneous body.
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From page 39... ...
If the permeability of the surrounding host rock is sufficiently small, the buildup in fluid pressure may be quite large. One other potential source of fluid flow into the crust is mantle degassing.
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From page 40... ...
On the maintenance of anomalous fluid pressures: II. Source layer at depth, Geological Society of America Bulletin 77, 1107- 1122.
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From page 41... ...
Gale (19834. Theory of Earth tide and barometric effects in porous formations with compressible grains, Water Resources Research 19, 538-544.
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