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Modeling Thermal Pressurization Around Shallow Dikes Using Temperature‐Dependent Hydraulic Properties: Implications for Deformation Around Intrusions
Author(s) -
Townsend Meredith R.
Publication year - 2018
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2017jb014455
Subject(s) - geology , cabin pressurization , porosity , dike , permeability (electromagnetism) , thermal diffusivity , pore water pressure , geothermal gradient , hydraulic conductivity , hydrostatic pressure , geotechnical engineering , mineralogy , petrology , soil science , geophysics , materials science , soil water , mechanics , composite material , physics , quantum mechanics , membrane , biology , genetics
Pressurization and flow of groundwater around igneous intrusions depend in part on the hydraulic diffusivity of the host rocks and processes that enhance diffusivity, such as fracturing, or decrease diffusivity, such as mineral precipitation during chemical alteration. Characterizing and quantifying the coupled effects of alteration, pore pressurization, and deformation have significant implications for deformation around intrusions, geothermal energy, contact metamorphism, and heat transfer at mid‐ocean ridges. Fractures around dikes at Ship Rock, New Mexico, indicate that pore pressures in the host rocks exceeded hydrostatic conditions by at least 15 MPa following dike emplacement. Hydraulic measurements and petrographic analysis indicate that mineral precipitation clogged the pores of the host rock, reducing porosity from 0.25 to <0.10 and reducing permeability by ~5 orders of magnitude. Field data from Ship Rock are used to motivate and constrain numerical models for thermal pore fluid pressurization adjacent to a meter‐scale dike, using temperature‐dependent hydraulic properties in the host rock as a proxy for porosity loss by mineral precipitation during chemical alteration. Reduction in permeability by chemical alteration has a negligible effect on pressurization. However, reduction in porosity by mineral precipitation increases fluid pressure by constricting pore volume and is identified as a potentially significant source of pressure. A scaling relationship is derived to determine when porosity loss becomes important; if permeability is low enough, pressurization by porosity loss outweighs pressurization by thermal expansion of fluids.