Water-rock interactions in fault gouge
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Fault gouge
Many Quaternary faults are recognized as thin gouge and narrow cataclastic zone juxtaposing the Bulguksa granite and Quaternary deposit bed in the eastern block of the Using Fault, Korea: Gaegok 1, Caegok 2, Singye, Madong Wonwonsa and Jinhyeon faults. This study was performed to calculate chemical change, volume change, silica loss and fluid-rock ratio taken place in gouge zones of these Quaternary faults using XRF, XRD, EPMA. The chemical compositions of fault rocks reveal that the fault gouges are depleted in and enriched in relative to protoliths. The fact that there is enrichment of relatively immobile elements and depletion of the more soluble elements in the fault gouges relative to protoliths can be explained by fluid-assisted volume loss of for Caegok 1 fault, for Caegok 2 fault,, for Singye fault, for Madong fault, for the Wonwonsa fault and for the linhyeon fault. Madong fault and Wonwonsa fault where ratios of the volume change, silica loss and fluid-rock are low might have acted as a closed system for fluid activity, whereas Caegok 1 fault and Jinhyeon fault with high ratios in those factors be an open system. The volumetric fluid-rock ratios range for all faults, being highest in Caegok 1 fault and Jinhyeon fault whose fluid activity was most significant
Fault gouge
Cataclastic rock
Protolith
Fault block
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Field, laboratory, and modeling studies of faulted rock yield insight into the hydraulic character of thrust faults. Late‐stage faults comprise foliated and subparallel faults, with clay‐rich gouge and fracture zones, that yield interpenetrating layers of low‐permeability gouge and higher‐permeability damage zones. Laboratory testing suggests a permeability contrast of two orders of magnitude between gouge and damage zones. Layers of differing permeability lead to overall permeability anisotropy with maximum permeability within the plane of the fault and minimum permeability perpendicular to the fault plane. Numerical modeling of regional‐scale fluid flow and heat transport illustrates the impact of fault zone hydrogeology on fluid flux, fluid pore pressure, and temperature in the vicinity of a crystalline thrust sheet.
Thrust fault
Fault gouge
Fault plane
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Fault gouge
Outcrop
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For regional and local isotopic investigations, it is important to compare isotopic data of surface water and groundwater with the local meteoric relationship for 18 O and in precipitations. In this paper, the Mashhad meteoric water line (MMWL) is defined for the first time, based on samples of precipitation collected from several rain stations located within and around of Mashhad city - NE of Iran. Both the slope and 2 H intercept for MMWL ( 2 H = 7.17 18 O + 11.22) are deviated from the global meteoric water line - GMWL ( 2 H = 8.13 18 O + 10.8). The huge variation in isotopic compositions of the Mashhad rain (from -198.2 to +38.1‰ and from -26.1 to +3.7‰ for 2 H and 18 O, respectively) is because of strong seasonal changes in precipitations in this area. The 2 H and 18 O isotopes of local water resources show evaporative enrichment in comparison with local meteoric water.
δ18O
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Mineral resource classification
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Gouge is the carrier for information of the fault activity.In this study,fault gouges from the eastern Liupanshan piedmont fault zone were analyzed by ESR method.However,the measured ESR age is much older than that estimated in the field.On the other hand,SEM images of the quartz grains separated from the fault gouge showed a variety of morphologies,which indicate several periods of fault movements.The ESR age estimates failing to represent the latest fault movement suggest that the latest movement may not have zeroed ESR signals significantly for ESR dating and the quartz may be from different periods of the movements.Although there are still many uncertain factors in the ESR dating of fault gouge,it is essential to study systematically in this area.
Fault gouge
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The permeability of a San Andreas fault gouge is determined under confining pressures up to 220 bars; it decreases with pressure from 10 nanodarcy at 15 bars to 0.3 nanodarcy at 220 bars. These values are lower than the values determined by Morrow et al. (1981). Five different samples of fault gouge with significantly different grain‐size distributions were sheared between rock joints under confining pressures to determine the effects of grain size and constitution on the strength of the fault gouge. The strength of fault gouge clearly depends on its constitution and grain size distribution, with the coarser sandy fault gouge being stronger than the finer clayey gouge. Furthermore, the coarser gouge tends to strain harden after yielding, leading to greater strength. Thus, on the San Andreas fault, inhomogeneities in gouge materials may cause spatial variations in strength. Using the permeability determined above, we estimate that the excess pore pressure generated in the fault gouge samples during the experimental shear loading may be negligible.
Fault gouge
Overburden pressure
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