Laboratory investigation of mechanisms for phase mixing in olivine + ferropericlase aggregates
Laboratory investigation of mechanisms for phase mixing in olivine + ferropericlase aggregates
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橄榄石--铁方镁石聚集体相混合机制的实验室研究
DOI：
10.1098/rsta.2017.0417
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
Kohlstedt, David L.
中科院分区：
文献类型：
--
作者：
Wiesman, Harison S.;Zimmerman, Mark E.;Kohlstedt, David L.
为了研究晶界钉扎的作用以及多矿物岩石变形过程中发生相混合的机制，我们对由橄榄石加 30% 方镁石组成的样品进行了高应变扭转实验。实验在气体介质变形装置中进行，温度为1524K，压力为300MPa。样品变形至外半径剪切应变高达γ(R) = 14.1。我们的样品的应力指数值和小晶粒尺寸表明我们的两相材料通过位错适应晶界滑动而变形。在变形为 1<γ< 7 的样品中，细长的方镁石晶粒簇在橄榄石基质中形成薄层，并且在橄榄石晶界和三晶粒和四晶粒交界处出现小晶粒。到γ≈ 14时，橄榄石颗粒中形成了均匀分布的小方镁石颗粒混合物。微观结构与用于描述导致相混合的过程的机械和化学模型表现出相似之处。我们的结果提供了相混合过程中晶粒尺寸减小的证据，这导致晶粒尺寸明显小于橄榄石单相再结晶压力计预测的值。因此，相混合提供了一种岩石持续弱化的机制，这对于板块构造所需的剪切带的形成和维持非常重要。本文是“地球动力学和板块构造的发展”讨论会议的一部分。
To investigate the role of grain boundary pinning and the mechanisms by which phase mixing occurs during deformation of polymineralic rocks, we conducted high-strain torsion experiments on samples consisting of olivine plus 30 vol% ferropericlase. Experiments were performed in a gas-medium deformation apparatus at 1524 K and 300 MPa. Samples were deformed to outer radius shear strains of up toγ(R) = 14.1. The value of the stress exponent and the small grain sizes of our samples indicate that our two-phase material deformed by dislocation-accommodated grain boundary sliding. In samples deformed to 1 <γ< 7, elongated clusters of ferropericlase grains form thin layers in the olivine matrix, and small grains of ferropericlase appear at olivine grain boundaries and three- and four-grain junctions. Byγ≈ 14, a well-distributed mixture of small ferropericlase grains among the olivine grains developed. Microstructures exhibit similarities to both mechanical and chemical models proposed to describe the processes leading to phase mixing. Our results provide evidence for grain size reduction during phase mixing that results in a grain size significantly smaller than the value predicted by the single-phase recrystallization piezometer for olivine. Thus, phase mixing provides a mechanism for the persistent weakening of rocks that is important for developing and maintaining shear zones necessary for plate tectonics.This article is part of a discussion meeting issue ‘Earth dynamics and the development of plate tectonics'.
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影响因子：
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作者：
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DOI：
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影响因子：
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