Date of Award:

5-1993

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geosciences

Department name when degree awarded

Geology

Committee Chair(s)

James P. Evans

Committee

James P. Evans

Committee

Craig B. Forster

Committee

Peter Kolesar

Committee

Tom Lachmar

Abstract

An integrated field, microstructure, fracture statistic , geochemistry, and laboratory permeability study of the East Fork and White Rock fault zones, of similar age and tectonic regime but different structural level and hydrogeologic history, provides detailed information about the internal deformation and fluid flow processes in fault zones. The primary conclusions of this research are: 1) Fault zones can be separated into subzones of protolith, damaged zone , and gouge /cataclasite, based on physical morphology and permeability structure. At deep structural levels, gouge/cataclasite zones are more evolved (thicker with increased grain size reduction) due to strain localization, higher pressure and temperature, and fluid/rock interaction; 2) Deformation mechanisms evolved from primarily brittle fracturing and faulting in the damaged zone to extreme, fluid-enhanced chemical breakdown and cataclasis which localized strain in the fault core. Deformation in the deep-level-fault core may be a combination of frictional and quasiplastic mechanisms, and is largely controlled by extremely fine-grained clays, zeolites, and other phyllosilicates that may have acted as a thermally pressurized, fluid-saturated lubricant; 3) Permeability in fault zones was temporally heterogeneous and anisotropic (permeability of damaged zone>protolith>gouge/cataclasite, permeability along fault> permeability across fault); 4) Volume loss was concentrated in the fault cores and was negligible at intermediate structural

levels and high at deep structural levels in the semi-brittle to brittle regime; 5) Fluid flow and solute transport were concentrated upwards and subparallel to the fault in the damaged zone; 6) Faults at both the local and regional scale acted as fluid flow conduit/barrier systems depending upon the evolutionary stage and interval in the seismic cycle; 7) Fluid/rock volume ratios, fluid flux, and fluid/rock volume ratios over time ranged from ⋍ 103 to 104, 10-6 ms-1 to 10-9 ms-1, and 0.05 L/m3 rock•yr to 0.50 L/m3 rock•yr, respectively, suggesting that enormous quantities of fluids passed through the fault zones; 8) Box counting fractal analyses of fault zone fractures showed that fracture spatial and density distribution is scale-invariant at the separate scales of outcrop , hand-sample , and thin section, but self-affine from outcrop to thin-section scale; 9) Linear fractal analysis depicts clustering and density distribution as a function of orientation, and may be a quick, robust method of estimating two-dimensional fracture permeability; and 10) Fractal analysis of fractures is not a comprehensive statistical method, but can be used as another supplemental statistical parameter.

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