石英-钠长石混合物中的脆-塑性转变：中下地壳深度条件下剪切变形实验的新见解
The Brittle-Plastic Transition in Quartz-Albite Mixtures: New Insights From Shear Deformation Experiments at Mid-to-Lower Crustal Depth Conditions
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中文总结 AI 辅助
通过Griggs装置对石英-钠长石混合物进行剪切实验，模拟7-30 km深度，发现摩擦-黏性转变带由晶界滑动和动态重结晶控制，纳米尺度机制主导上地壳地震破裂过程。
中文摘要 AI 辅助
地壳强度通常使用强度-深度剖面来表征，其中实验室得出的摩擦定律和流动定律在深度上相连接（即所谓的圣诞树图）。大型破坏性地震经常在从摩擦变形体制到黏性变形体制的转变带内成核，该转变带代表了地壳最强的部分。然而，控制整体摩擦-黏性转变行为的微观变形机制仍不清楚。为了研究这些变形机制，我们使用Griggs型变形装置，在上地壳至中地壳的压力-温度条件下，对室温干燥的粉状石英-钠长石混合物进行了剪切实验。我们通过改变温度和围压（分别假设30°C/km和2700 kg/m³，温度范围为210-900°C，围压范围为185-870 MPa），模拟了7-30 km的深度条件。为了评估剪切变形的速率依赖性和稳定性，我们依次将剪切应变速率在10^-3/s和10^-4/s之间步进切换。在较浅的深度条件下，摩擦系数遵循拜尔利定律，而在较深的深度条件下，摩擦系数偏离该定律，并观察到应变弱化现象。实验后的微观结构表明，随着模拟深度的增加，变形机制发生变化。在较浅深度条件（<18 km）下变形的样品显示出碎裂性颗粒粉碎的主导作用。在较深深度条件（>24 km）下，观察到纳米颗粒，并且在最大深度条件（30 km）下观察到多边形石英颗粒。这些结果表明，在摩擦-黏性转变带中，控制变形机制是晶界滑动和动态重结晶。我们得出结论，纳米尺度变形机制控制着上地壳中的摩擦-黏性转变变形，并提出它们对于理解该处地震破裂过程的重要性。
英文摘要
Crustal strength is often characterized using a strength-depth profile where laboratory-derived friction and flow laws are connected at depth (i.e., the so-called Christmas Tree diagram). Large, destructive earthquakes frequently nucleate within the transition zone from a frictional-to-viscous deformation regime, which represents the strongest part of the crust. However, microscale deformation mechanisms controlling bulk frictional-to-viscous transitional behavior remain unclear. To investigate the deformation mechanisms, we conducted shear experiments on room-dry, powdered quartz-albite mixtures under upper- to mid-crustal pressure-temperature conditions using a Griggs-type deformation apparatus. We simulated depth conditions in the range 7-30 km, by varying temperatures and confining pressures (210-900 C and 185-870 MPa, respectively, by assuming 30 C/km and 2,700 kg/m3). To assess the rate dependence and stability of shear deformation, we sequentially stepped shear strain rates between 10^-3/s and 10^-4/s. At shallower depth conditions, friction coefficients follow Byerlee's law, while at greater depth conditions they deviate from it and strain weakening is observed. Post-mortem microstructures indicate changing deformation mechanisms with increasing simulated depths. The samples deformed at shallower depth conditions (<18 km) show a predominance of cataclastic grain comminution. At greater depth conditions (>24 km), nano-grains are observed, as well as polygonal quartz grains at the greatest depth condition (30 km). These results indicate that the controlling deformation mechanisms at the frictional-viscous transition zone are grain boundary sliding and dynamic recrystallization. We conclude that nano-scale deformation mechanisms govern the frictional-viscous transitional deformation in the upper crust, and propose their importance for understanding seismic rupture processes there.
发表机构
- Tohoku University（东北大学）
- Geological Survey of Japan, The National Institute of Advanced Industrial Science and Technology（日本地质调查局，产业技术综合研究所）
- Utrecht University（乌得勒支大学）
- University of Bremen（不来梅大学）
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