Structural and fluid-chemical properties of fault zones

Conference · Wed Jan 01 00:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5880186

Bruhn, R L ^[1]

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1. Univ. of Utah, Salt Lake City, UT (United States). Dept. of Geology and Geophysics

Fault fluids are mostly NaCl-CO[sub 2]-H[sub 2]O mixtures that originate by metamorphism, escape of connate water from wall rock, circulation of meteoric water, and perhaps contain components derived form igneous and subcrustal sources. Rupturing extends downward into metamorphic terrains undergoing greenschist and amphibolite facies metamorphism, where mineral alteration triggered by fluid pressure transients may extend several hundred meters to perhaps several kilometers into the wall rock. Fluid flowing into regions of lower temperature and/or pressure causes retrograde metamorphic alteration of fault and wall rock, and cementation of fractures. Fault permeability is heterogeneous because irregular, discontinuous lenses of cataclastic and gouge are encased in a heterogeneous damage layer characterized by intense fracturing and hydrothermal alteration. Permeability is also controlled by the geometry of corrugated slip surfaces which create anisotropic flow channels with greatest permeability parallel to long-axes of corrugations. Mineral assemblages and fluid inclusions provide evidence for fluid pressure cycling. Fluid pressure drops when permeability is enhanced by rupturing and subsequently increases as fractures deform, heal and become cemented with alteration minerals. Rates of hydrothermal alteration are comparable to, and sometimes faster, than those of mechanically induced permeability reduction. Effects of fluid chemistry on fault mechanics are not as well understood as fluid pressure effects. Frictional properties of fault surfaces are changed by chemical corrosion, cementation, and pressure solution. Strengthening by fluid pressure drop during dilatant fracturing may be partially offset by a decrease in fluid bulk modulus triggered by effervescence of CO[sub 2].

• OSTI ID: 5880186
• Report Number(s): CONF-921058-; CODEN: GAAPBC
• Journal Information: Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GEOLOGIC FAULTS
ROCK-FLUID INTERACTIONS
CARBON DIOXIDE
FRICTION
GEOCHEMISTRY
GEOLOGIC FRACTURES
HYDROTHERMAL ALTERATION
METAMORPHISM
ORIGIN
PERMEABILITY
RESERVOIR PRESSURE
ROCK MECHANICS
SODIUM CHLORIDES
WATER
ALKALI METAL COMPOUNDS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMISTRY
CHLORIDES
CHLORINE COMPOUNDS
GEOLOGIC STRUCTURES
HALIDES
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
MECHANICS
OXIDES
OXYGEN COMPOUNDS
SODIUM COMPOUNDS
580000* - Geosciences