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Brittle creep in basalt and its application to time-dependent volcano deformation

Brittle creep in basalt and its application to time-dependent volcano deformation,10.1016/j.epsl.2011.04.035,Earth and Planetary Science Letters,M. J.

Brittle creep in basalt and its application to time-dependent volcano deformation   (Citations: 2)
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Time-dependent brittle deformation is a fundamental and pervasive process operating in the Earth's upper crust. Its characterization is a pre-requisite to understanding and unraveling the complexities of crustal evolution and dynamics. The preferential chemical interaction between pore fluids and strained atomic bonds at crack tips, a mechanism known as stress corrosion, allows rock to fail under a constant stress that is well below its short-term strength over an extended period of time; a process known as brittle creep. Here we present the first experimental measurements of brittle creep in a basic igneous rock (a basalt from Mt. Etna volcano) under triaxial stress conditions. Results from conventional creep experiments show that creep strain rates are highly dependent on the level of applied stress (and can be equally well fit by a power law or an exponential law); with a 20% increase in stress producing close to three orders of magnitude increase in creep strain rate. Results from stress-stepping creep experiments show that creep strain rates are also influenced by the imposed effective confining pressure. We show that only part of this change can be attributed to the purely mechanical influence of an increase in effective pressure, with the remainder interpreted as due to a reduction in stress corrosion reactions; the result of a reduction in crack aperture that restricts the rate of transport of reactive species to crack tips. Overall, our results also suggest that a critical level of crack damage is required before the deformation starts to accelerate to failure, regardless of the level of applied stress and the time taken to reach this point. The experimental results are discussed in terms of microstructural observations and fits to a macroscopic creep law, and compared with the observed deformation history at Mt. Etna volcano.
Journal: Earth and Planetary Science Letters - EARTH PLANET SCI LETT , vol. 307, no. 1, pp. 71-82, 2011
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    • ...Failure of this type has been previously observed for low porosity basalts [Heap et al., 2009, 2011]...
    • ... surface that results in a substantial increase in radon emission rate (Figure 2). In contrast, radon emission rate measured from our ‘damaged’ sample did not show any significant variation with respect to that from the intact sample (Figure 2). Notably, previous studies on low porosity basalts have demonstrated that a significant portion of the damage required for failure is produced immediately prior to macroscopic sample rupture [Heap et ...

    S. Molloet al. Increase in radon emission due to rock failure: An experimental study

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