Brittle creep in basalt and its application to time-dependent volcano deformation
Brittle creep in basalt and its application to time-dependent volcano deformation
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DOI：
10.1016/j.epsl.2011.04.035
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发表时间：
2011-07-01
影响因子：
5.3
通讯作者：
Main, I. G.
中科院分区：
文献类型：
--
作者：
Heap, M. J.;Baud, P.;Main, I. G.
时间相关的脆性变形是地球上地壳中一个基本的和普遍的过程。它的特性是理解和揭示地壳演化和动力学复杂性的先决条件。孔隙流体和裂纹尖端的应变原子键之间的优先化学相互作用，一种称为应力腐蚀的机制，允许岩石在长时间内在远低于其短期强度的恒定应力下破坏：一个称为脆性蠕变的过程。在这里，我们提出了第一个实验测量脆性蠕变的基本火成岩（玄武岩从山。埃特纳火山）在三轴应力条件下。从传统的蠕变实验结果表明，蠕变应变率是高度依赖于所施加的应力水平（并可以同样很好地拟合幂律或指数律）：与20%的应力增加产生接近三个数量级的蠕变应变率增加。从应力步进蠕变实验结果表明，蠕变应变速率也受到所施加的有效围压。我们表明，只有部分的这种变化可以归因于纯粹的机械影响的有效压力的增加，其余的解释为由于应力腐蚀反应的减少，减少裂纹孔径的结果，限制反应性物种的运输速率裂纹尖端。总的来说，我们的研究结果还表明，在变形开始加速到失效之前，需要临界水平的裂纹损伤，无论施加的应力水平和达到这一点所需的时间如何。从微观结构观察的角度讨论了实验结果，并拟合了宏观蠕变规律，并与Mt.观察到的变形历史进行了比较。埃特纳火山。(c)2011 Elsevier B.V.保留所有权利。
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. (c) 2011 Elsevier B.V. All rights reserved.