Internal Deformation, Evolution, and Fluid Flow in Basement-Involved Thrust Faults, Northwestern Wyoming

• Main Author: Goddard, James V.
• Format: Others
• Published: DigitalCommons@USU 1993
• Subjects: Internal Deformation; Evolution; Fluid Flow; Basement; Thrust Fault; Wyoming; Geology
• Online Access: https://digitalcommons.usu.edu/etd/6697; https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=7752&context=etd

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.