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    Fluid flow in accretionary prisms
    Geol. Soc. Am., Abstr. Programs; (United States) (1985)
    P.J. VrolijkJ. Casey MooreJames R. O’Neil
    Fluid expulsion from actively deforming accretionary prisms occurs primarily along faults because matrix permeability is low, tectonic consolidation is rapid, and fluid pressures are high. Field observational, geophysical, and geochemical data from modern (Barbados, Oregon/Washington, and S. Mexico) and ancient (Kodiak, Alaska) setting show: 1) that fault zones (=melanges) are primary conduits of fluid flow and preserve a unique history of that fluid evolution; 2) that fluid flow is rapid and episodic; 3) and that with increasing deformation chemical systems in active faults become more rock dominated and contain more homogeneous fluids. 1) In modern accretionary environments near lithostatic fluid pressures and temperature anomalies suggest fault zones are preferential conduits of fluid flow. 2) Temperature discontinuities measured along modern faults (..delta..T approx. 12/sup 0/C) and vein/wall rock temperature contrasts in ancient rocks (..delta..T approx. 25-30/sup 0/C, from fluid inclusions) both indicate fluids move significant distances before heat dissipates). 3) During initial deformation, substantial movement of fluids along faults assures complete mixing. Sr/Ca measurements indicate waters evolve from seawater, and delta 18-0 analyses of calcite cements and veins (18-23 percent per thousand SMOW) suggest that for T < approx. 125/sup 0/C calcite crystallizes from unaltered seawater (..delta.. 18-0 approx. 0 percent more » per thousand). As melanges become increasingly pulverized and as temperatures rise, the calculated delta 18-0 value of water increases to approx. 12-14 percent per thousand, reflecting a decrease in apparent water/rock ratio and significant exchange with the host rock. The increased fault density serves to obliterate differences in delta 13-C (-10-0 percent per thousand) and homogenize fluids. « less
    Accretionary wedge
    Citations (4)
    Constraining fault architecture and fluid flow using crustal noble gases
    Applied Geochemistry (2021)
    William EymoldTalor B. WalshJoachim MoortgatBenjamin S. GroveThomas H. Darrah
    Thrust fault
    Hydrocarbon exploration
    Citations (5)
    Active fault participation in the diagenetic modification of sandstone reservoir properties
    AAPG Bulletin (1991)
    Stuart D. BurleyJ. WalshJ. Watterson
    In sedimentary basins undergoing regional strain, faults have a potential for influencing subsurface fluid flow by providing some of the driving energy for fluid movement. Variable displacement on faults in the slip direction results in systematic volume changes in the surrounding sedimentary rocks. Compressed and dilated volumes are distributed according to position relative to the fault. Intermittent seismic slip produces rapid pressure changes and high hydraulic gradients capable of causing movement of large fluid volumes or of maintaining pressure differentials if pore fluid migration is obstructed. As a result of the hydraulic gradients generated by individual faults, subsurface fluids may either be transferred between formations juxtaposed across the fault or vertically transported along the fault. Faults may thus provide the means of mixing of subsurface fluids, and are potentially zones of intense diagenetic modification. An appreciation of fault-influenced diagenetic modification is particularly pertinent to an understanding of the heterogeneity of sandstone reservoirs where pore water and hydrocarbon migration from source to reservoir rocks are an integral part of the hydrocarbon accumulation process. Mineralogical and fabric modifications to rock components may result in either significant enhancement of porosity or extensive cementation and compaction that overprints regional burial diagenetic assemblages. Inactive ormore » cemented faults may behave as hydrocarbon seals. The potential contribution of faults to sandstone reservoir heterogeneity should always be considered in models of burial diagenesis and hydrocarbon migration.« less
    Cementation (geology)
    Fluid pressure
    Petroleum reservoir
    Citations (1)
    Mass removal and clay mineral dehydration/rehydration in carbonate‐rich surface exposures of the 2008 Wenchuan Earthquake fault: Geochemical evidence and implications for fault zone evolution and coseismic slip
    Journal of Geophysical Research Solid Earth (2013)
    Jianye ChenXiao‐Song YangShengli MaChristopher J. Spiers
    We report variations in the mineralogical, geochemical, and isotopic ( δ 13 C, δ 18 O) composition of fault rocks sampled in transects across the Zhaojiagou and Pingxi exposures of the Wenchuan Earthquake or Longmenshan Fault Zone, where the gouge‐rich fault core and principal slip surface cuts through carbonate‐rich strata. Pervasive fluid infiltration was found to modify the mineralogical and geochemical architecture of the fault zones studied. Enrichment/depletion patterns, element partitioning, and a very large implied volume loss are quite different from those characterizing faults in granites and clastic sedimentary rocks and can be explained by a mass removal model involving dissolution and advective transport enhanced by pressure solution. An increasing enrichment in smectite observed toward the principal slip surface, a high abundance of elements such as Ba, Mg, and F, the deposition of minerals such as barite and fluorapatite, as well as the distinct depletion in 13 C in vein material consistently suggest reactions involving a hydrothermal fluid originating at depth. Illitization of black gouges, caused by coseismic frictional heating, was found to be widespread. We propose that coseismic frictional heating along with the action of postseismic hydrothermal fluids controlled the transformation and distribution of smectite and illite within the fault core of the Longmenshan Fault Zone. The coseismic dewatering reactions are expected to have been more extensive at depth, possibly helping generate excess pore pressure assisting dynamic slip weakening during the Wenchuan Earthquake.
    Illite
    Pressure solution
    Citations (49)