Olivine Morphology and Fabric During Diffusion Creep: Pure Shear Experiments
Olivine Morphology and Fabric During Diffusion Creep: Pure Shear Experiments
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DOI：
10.1029/2021jb023613
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发表时间：
2022-04
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影响因子：
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通讯作者：
N. Kim;T. Ando;K. Yabe;T. Hiraga
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作者：
N. Kim;T. Ando;K. Yabe;T. Hiraga
我们在纯剪切中使无铁橄榄石 + 20 vol% 透辉石的聚集体变形，以研究扩散蠕变过程中的橄榄石晶粒形态和结构。每个样品在不同温度和实验持续时间下变形至约 0.7 的应变，由于晶粒生长，导致样品之间的晶粒尺寸不同。从三个主应力方向中的每一个方向观察样品的微观结构，揭示了样品之间的各种 3D 晶粒形态。具有板状晶粒的样品在橄榄石中表现出晶体择优取向（CPO），而具有弱各向异性晶粒的样品则具有均匀的 CPO。 CPO模式从AG型（即样品缩短方向上的单轴[010]浓度）到A型（即样品缩短和拉伸方向上的[010]和[100]浓度分别）不同，其中中间类型是最常见的。从 AG 型织物到 A 型织物的转变伴随着从扁圆形到长圆形的纹理形态的变化。我们基于较少台阶（壁架）的边界处的优先晶界滑动（GBS）解释了橄榄石形态和织物之间的直接相关性。具有平行于（010）方向的发达晶界的扁圆形貌分别提供沿着（010）和[h0l]平面和方向的容易的GBS，而具有平行于（010）且沿着[100]拉长的晶界的相对长形形貌分别提供沿着（010）和[100]平面和方向的容易的GBS。通过沿晶轴方向的差异晶粒生长，形成平行于特定晶面的边界。这种晶粒生长会在扩散蠕变过程中引起织物转变。
We deformed aggregates of Fe‐free olivine +20 vol% diopside in pure shear to study olivine grain morphology and fabric during diffusion creep. Samples were each deformed to a strain of around 0.7 at different temperatures and experimental durations, which resulted in different grain sizes among the samples due to grain growth. The sample microstructures were observed from each of the three principal stress directions, which revealed various 3D grain morphologies among the samples. Samples with tabular grains displayed a crystallographic preferred orientation (CPO) in olivine, while samples with weakly anisotropic grains had uniform CPOs. The CPO patterns vary from AG‐type (i.e., a uniaxial [010] concentration in the direction of sample shortening) to A‐type (i.e [010] and [100] concentrations in the directions of sample shortening and stretching, respectively), with intermediate types being the most common. The transition from AG‐ to A‐type fabrics is accompanied by a change from oblate to prolate grain morphologies. We explain the direct correlation between the olivine morphology and fabrics based on preferential grain‐boundary sliding (GBS) at boundaries with fewer steps (ledges). Oblate morphologies with well‐developed grain boundaries oriented parallel to (010) provide easy GBS along (010) and [h0l] planes and directions, respectively, while relatively prolate morphologies with boundaries parallel to (010) that are elongated along [100] provide easy GBS along (010) and [100] planes and directions, respectively. Boundaries form parallel to a particular crystallographic plane through differential grain growth in the directions of the crystallographic axes. Such grain growth causes fabric transitions during diffusion creep.