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Coupling of fluid flow to permeability development in mid- to upper crustal environments: a tale of three pressures

By
Bruce E. Hobbs
Bruce E. Hobbs
CSIRO, Perth, WA 6102, AustraliaCentre for Exploration Targeting, University of Western Australia, WA 6009, Australia
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Alison Ord
Alison Ord
Centre for Exploration Targeting, University of Western Australia, WA 6009, AustraliaSchool of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009, China
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Published:
January 01, 2018

Abstract

Orogenic gold systems are open, flow-controlled thermodynamic systems and generally occur in mid- to upper crustal environments where there is strong coupling between fluid flow and dilatant plastic deformation. This paper considers the principles involved in such coupling, with an emphasis on the elastic and plastic volume changes and their influence on the fluid, mechanical and thermodynamic pressures. Some misconceptions regarding the magnitudes of these three distinctly different pressures and their influences on fluid flow and chemical equilibrium are addressed, with examples at both the tens of metres scale and the crustal scale. We show that the mean stress is less than twice the lithostatic stress for Mohr–Coulomb materials with cohesion and the thermodynamic pressure only has meaning under isentropic conditions and hence is less than many previously published estimates based on high mean stresses. At the crustal scale, we also include the role of critical behaviour in influencing the geometry and magnitudes of fluid pressure gradients and fluid flow velocities in open, flow-controlled systems.

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Geological Society, London, Special Publications

Characterization of Ore-Forming Systems from Geological, Geochemical and Geophysical Studies

K. Gessner
K. Gessner
Geological Survey of Western Australia, Australia
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T.G. Blenkinsop
T.G. Blenkinsop
Cardiff University, UK
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P. Sorjonen-Ward
P. Sorjonen-Ward
Geological Survey of Finland, Finland
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Geological Society of London
Volume
453
ISBN electronic:
9781786203342
Publication date:
January 01, 2018

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