Low-temperature plasticity of olivine during high stress deformation of peridotite at lithospheric conditions - An experimental study
Low-temperature plasticity of olivine during high stress deformation of peridotite at lithospheric conditions - An experimental study
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DOI：
10.1016/j.epsl.2011.09.022
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发表时间：
2011-11-15
影响因子：
5.3
通讯作者：
Hanke, Karin
中科院分区：
文献类型：
--
作者：
Druiventak, Anthony;Trepmann, Claudia A.;Hanke, Karin
挪威Almklovdalen杂岩天然橄榄岩的变形实验是在Griggs型装置中进行的，温度分别为20、300和600℃，围压为1.0至2.5 GPa，应变速率为3.10(-6)至8. 10(-5) s(-1)。实验产生 1.0 至 2.9 GPa 范围内的最大差应力，大部分落在拜尔利定律和格策准则之间，因此表明半脆性行为。虽然在20℃变形的样品强度随着围压的增加而显着增加，但在300℃和600℃时强度的系统压力依赖性并不明显。通过光和电子显微技术（SEM/EBSD、TEM）分析了主成分橄榄石的晶内变形特征。变形微观结构随温度系统地变化，但对围压不敏感。 20°C 下变形的样品主要反映了晶内微裂纹和剪切区导致的脆性破坏。在较高温度下变形的样品的微观结构显示了橄榄石的低温塑性，其形式为与高位错密度相关的明显波状消光。位错的堆积导致在 300°C 时形成断裂阵列，或在 600°C 时形成平行 (100) 变形片层和蜂窝结构，表明晶内加工硬化。随着温度升高，橄榄石滑动控制的晶体塑性变形逐渐增加，这被解释为机械行为和微观结构特征变化的原因。力学数据和微观结构观察一致表明，从脆性控制强度主导向晶体塑性变形机制转变的温度接近 600 摄氏度。在可比实验条件下，测试的橄榄岩样品显示出比石英岩样品更低的强度，可能与橄榄石和石英的晶体学差异有关。实验变形橄榄岩和自然变形橄榄岩的微结构之间的一致性证明了橄榄石在岩石圈条件下高应力变形期间的低温塑性的重要性，特别是与地幔地震活动相关的条件。 (C) 2011 Elsevier B.V. 保留所有权利。
Deformation experiments on natural peridotite from the Almklovdalen complex, Norway, were carried out in a Griggs-type apparatus at temperatures of 20, 300, and 600 degrees C. confining pressures of 1.0 to 2.5 GPa, and strain rates of 3.10(-6) to 8. 10(-5) s(-1). The experiments yield maximum differential stresses in the range of 1.0 to 2.9 GPa falling mostly between Byerlee's law and Goetze's criterion and thus indicating semi-brittle behaviour. Whereas strength of samples deformed at 20 degrees C increases significantly with increasing confining pressure, a systematic pressure-dependence of strength is not obvious at 300 and 600 degrees C. The intracrystalline deformation features of the main constituent olivine were analysed by light and electron microscopic techniques (SEM/EBSD, TEM). Deformation microstructures systematically vary with temperature, but are insensitive to confining pressure. Samples deformed at 20 degrees C reflect predominantly brittle failure by intragranular microcracks and shear zones. Microstructures from samples deformed at higher temperatures show evidence of low-temperature plasticity of olivine in the form of pronounced undulatory extinction associated with high dislocation densities. Pile-up of dislocations leads to the formation of either fracture arrays at 300 degrees C or deformation lamellae parallel (100) and cellular structures at 600 degrees C, indicating intragranular work hardening. A gradual increase in glide-controlled crystal-plastic deformation of olivine at increasing temperature is interpreted to be responsible for the variation in mechanical behaviour and microstnictural characteristics. The mechanical data and microstructural observations consistently suggest a temperature for the transition from the strength-controlling dominance of brittle to crystal-plastic deformation mechanisms close to 600 degrees C. The tested peridotite samples show a lower strength than quartzite samples at comparable experimental conditions, possibly related to crystallographic differences of olivine and quartz. The agreement between microfabrics of experimentally and naturally deformed peridotites demonstrates the importance of low-temperature plasticity of olivine during high-stress deformation at lithospheric conditions related in particular to seismic activity in the mantle. (C) 2011 Elsevier B.V. All rights reserved.