Fluid-rock interactions in semi-brittle to brittle fault zones
- Utah State Univ., Logan, UT (United States). Dept of Geology
An integrated field, microstructure, fracture statistic, geochemistry, and laboratory permeability study of the East Fork and White Rock fault zones in northwest Wyoming, of similar age and tectonic regime but different structural level and hydrogeologic history, provided detailed information about the internal deformation and fluid flow processes in fault zones. The two fault zones can be separated into: (1) unaltered granitic protolith in which permeability is relatively intermediate, homogeneous, and isotropic; (2) fault-subparallel intra- and intergranularly fractured, veined, and subsidiary faulted damaged zone in which permeability is relatively high, heterogeneous with respect to local variations of fracture density and interconnectivity, and anisotropic with flow concentrated in open micro- and macroscopic fractures in directions subparallel to the fault; and (3) gouge, cataclasite, and ultracataclasite in which permeability is mostly extremely low, acting as a fluid flow barrier and pressure seal especially for flow across the fault. The dominant deformation mechanisms within the East Fork fault zones were brittle fracture, comminution, and subsequent late stage hydrolysis of feldspar to clays. The White Rock fault deformation is characterized by brittle fracturing and faulting in the damaged zone and extreme, fluid-assisted cataclasis in the fault core, which led to large-scale comminution and dissolution of feldspar, quartz, and mica to produce: (1) clays, zeolite, and phyllosilicates; (2) concomitant enrichments in immobile components; and (3) loss of silica and alkalies to an infiltrating fluid resulting in large volume losses of about 30% to 80% and fluid/rock volume ratios between 10[sup 3] to 10[sup 4]. Progressive grain size reduction and fluid-enhanced chemical breakdown of quartz, feldspar, and mica within the fault zone initiated strain softening and localization as cataclasite and ultracataclasite developed.
- OSTI ID:
- 5019661
- Report Number(s):
- CONF-9305259--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 25:5; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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