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Reduction of permeability in granite at elevated temperatures.
Science (New York, N.Y.)
|September 9, 1994
Summary
Hydrothermal fluids reduce granite permeability between 300-500°C, especially with added gouge. This supports the fault-valve model for ore deposit formation and fault sealing.
Area of Science:
- Geology
- Geochemistry
- Tectonics
Background:
- Understanding fault zone processes is crucial for resource exploration and seismic hazard assessment.
- Hydrothermal alteration plays a significant role in modifying rock properties within fault zones.
Purpose of the Study:
- To investigate the impact of hydrothermal fluids on granite permeability at elevated temperatures.
- To evaluate the role of gouge material in accelerating permeability reduction.
- To assess the implications for the fault-valve model and mineral sealing in fault zones.
Main Methods:
- Experimental study involving the addition of hydrothermal fluids to heated, intact granite.
- Testing conducted within a specific temperature range (300-500°C).
- Inclusion of gouge material to assess its effect on permeability.
Main Results:
- Permeability of granite significantly reduced in the 300-500°C range.
- Permeability reduction rate increases with temperature.
- Gouge material accelerates permeability reduction due to enhanced reactivity.
- Flow rate in fractures decreases to the level of intact granite over time.
Conclusions:
- Results support the fault-valve model for mesothermal ore deposit genesis.
- Mineral sealing at the base of the seismogenic zone of thrust faults is supported.
- Observed sealing rates at lower temperatures align with hypotheses for fault zone sealing relative to earthquake recurrence intervals.
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