Pore-fluid chemistry and chemical reactions on the Wasatch normal fault, Utah

Journal Article · Mon Aug 01 04:00:00 EDT 1988 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(88)90184-6· OSTI ID:7018016

Parry, W T; Wilson, P N; Bruhn, R L ^[1]

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1. Univ. of Utah, Salt Lake City (USA)

Mineral assemblages and fluid inclusions (F.I.) in hydrothermally altered and tectonically deformed Oligocene quartz monzonite in the footwall of the active Wasatch normal fault, Utah have been used to estimate fluid pressure, temperature, chemical composition, and chemical reactions associated with progressive displacement of the fault. Vein filling and pervasive alteration mineralogy includes (earliest to latest) biotite-K-feldspar, chlorite-epidote-sericite, and laumontite-prehnite-clay. Secondary F.I. in quartz, associated with chlorite-epidote-sericite alteration, consist of CO{sub 2} and salt solution; the homogenization temperature mode is 285{degree}C, X{sub CO{sub 2}} is 0.03-0.32, and salinity ranges from 4.5-17.3 wt % NaCl equivalent; estimated minimum entrapment pressures vary from 600-2950 bars. The homogenization temperature mode of secondary F.I. associated with the laumontite-prehnite assemblage is 100{degree}C, salinity ranges from 2.0-16.0 wt% NaCl equivalent, and no CO{sub 2} was detected; entrapment pressures are presumed to have been hydrostatic and below 460 bars. Fluid pressure and temperature evolved along a path from lithostatic to hydrostatic with continued displacement of the footwall relative to the hanging wall. Age constraints are provided by a 17.6 {plus minus} 0.6 m.y. K-Ar age of hydrothermal sericite from a sample with mean T{sub h} of 309{degree}C, and 7.3 to 9.6 m.y. fission track ages of apatite (closure temperature 120 {plus minus} 15{degree}C). The hot aqueous fluids affect the mechanical behavior of the rock during faulting. Crack sealing by alteration product minerals reduces permeability, and the effective stress is decreased by pore fluid pressures substantially greater than hydrostatic in the early alteration.

• OSTI ID: 7018016
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Vol. 52:8; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
CENOZOIC ERA
CHEMICAL COMPOSITION
CHEMISTRY
EQUILIBRIUM
FEDERAL REGION VIII
FELDSPARS
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
HYDROTHERMAL ALTERATION
IGNEOUS ROCKS
INCLUSIONS
ISOTOPE DATING
MINERALIZATION
MINERALOGY
MINERALS
NORTH AMERICA
PHASE STUDIES
PLUTONIC ROCKS
ROCKS
SALINITY
TERTIARY PERIOD
USA
UTAH