Выпуск 378
Автор(ы):Shimamoto T., Uehara S.
Издание:Journal Tectonophysics, 2004 г., 13 стр.
Gas permeability evolution of cataclasite and fault gouge in triaxial compression and implications for changes in fault-zone permeability structure through the earthquake cycle

We report the results of permeability measurements of fault gouge and tonalitic cataclasite from the fault zone of the Median Tectonic Line, Ohshika, central Japan, carried out during triaxial compression tests. The experiments revealed marked effects of deformation on the permeability of the specimens. Permeability of fault gouge decreases rapidly by about two orders of magnitude during initial loading and continues to decrease slowly during further inelastic deformation. The drop in permeability during initial loading is much smaller for cataclasite than for gouge, followed by abrupt increase upon failure, and the overall change in permeability correlates well with change in volumetric strain, i.e., initial, nearly elastic contraction followed by dilatancy upon the initiation of inelastic deformation towards specimen failure. If cemented cataclasite suffers deformation prior to or during an earthquake, a cataclasite zone may change into a conduit for fluid flow. Fault gouge zones, however, are unlikely to switch to very permeable zones upon the initiation of fault slip. Thus, overall permeability structure of a fault may change abruptly prior to or during earthquakes and during the interseismic period. Fault gouge and cataclasite have internal angles of friction of about 36j and 45j, respectively, as is typical for brittle rocks.

ТематикаРегиональная геология
МеткиCataclasite, Earthquake, Fault gouge, Fluid flow, Median Tectonic Line, Permeability, Triaxial deformation, Землетрясения, Катаклазиты, Флюиды
Выпуск 340
Автор(ы):Labaume P., Moretti I., Sheppard S.M.F.
Издание:Journal Tectonophysics, 2001 г., 32 стр.
Fluid flow in cataclastic thrust fault zones in sandstones, Sub-Andean Zone, southern Bolivia

The Bolivian Sub-Andean Zone (SAZ) corresponds to a Neogene thrust system that affects an about 10-km thick Palaeozoic to Neogene siliciclastic succession. The analysis of macro and microstructures and cement distribution in thrust fault zones shows that they are sealed by quartz at depths > 3 km, due to local silica transfer by pressure-solution/precipitation activated at temperatures >70–90 C. At shallower depths, faults have remained open and could be preferential drains for lateral flow of carbonate-bearing fluids, as shown by the occurrence of carbonate cements in fractures and their host-sandstone. Due to decreasing burial, resulting from foothill erosion during fault activity, critically buried fault segments can be affected by nonquartz-sealed structures that post-date initial quartz-sealed structures. The integration of textural, fluid inclusion and isotopic data shows that carbonates precipitated at shallow depth ( < 3 km), low temperature ( < 80 C) and relatively late during the thrusting history. Isotopic data also show that precipitation occurred from the mixing of gravity-driven meteoric water with deeper formation water bearing carbonate carbon derived from the maturation of hydrocarbon source rocks (Silurian and Devonian shales). The combined microstructural and isotopic analyses indicate that: (i) fluid flow in fault zones often occurred with successive pulses derived from different or evolving sources and probably related to episodic fault activity, and (ii) at a largescale, the faults have a low transverse permeability and they separate thrust sheets with different fluid histories. 

МеткиBolivia, Carbon isotopes, Cataclasis, Cement, Fault zone, Fluid flow, Oxygen isotopes, Sub-Andean Zone, Анды, Боливия, Изотопия, Песчаники
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