Evolution of crystal orientation in snow during temperature gradient metamorphism
Evolution of crystal orientation in snow during temperature gradient metamorphism
复制标题
温度梯度变质过程中雪中晶体取向的演变
DOI：
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发表时间：
2013
影响因子：
3.4
通讯作者：
M. Schneebeli
中科院分区：
文献类型：
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作者：
F. Riche;M. Montagnat;M. Schneebeli
摘要雪的物理性质与其微观结构密切相关。特别是对于雪和雪的缓慢塑性变形，除了冰基质的几何形状外，晶体取向也是一个重要因素。虽然微型计算机断层扫描精确地测量了雪的微结构，但它没有提供关于冰晶方向的信息。在这项研究中，我们在3个月的时间里对原状分解雪和筛分后的大块雪施加了50Km−1的温度梯度。在温度梯度实验中，雪样的平均温度为−20°C，在实验前，然后在第一个月中每周采集一次雪样，之后每个月采集两个密排的雪样。在每次取样中，一个样品用微型计算机断层扫描进行分析，另一个样品用来做薄片。用自动冰纹分析仪测量薄片中c轴的取向。筛分后的雪样的初始密度要高出30%。密度和比表面积的变化相似，而织物在两个样品之间表现出不同的变化。原状雪由弱单峰组构向弱带状组构演化，而筛分后的样品没有演化。未受干扰的雪样在6周后向筛样织物汇聚，但此后继续演变。我们认为，导致这种不同行为的主要因素是密度和孔径的差异。
Abstract The physical properties of snow are tied to its microstructure. Especially for the slow, plastic deformation of snow and firn, the crystal orientation is an important factor in addition to the geometry of the ice matrix. While micro-computed tomography measures the snow microstructure precisely, it gives no information about the orientation of the ice crystals. In this study, we applied a temperature gradient of 50 K m−1 to large blocks of undisturbed decomposed snow and sieved snow during 3 months. The mean temperature of the snow samples during the temperature gradient experiment was −20°C. Two closely spaced snow samples were taken before the experiment, then every week during the first month and afterwards every month. From each sampling, one sample was analyzed by micro-computed tomography and the other was used for thin sections. The orientation of the c-axis was measured in the thin sections using an automatic ice texture analyzer. Initial density was 30% higher in the sieved snow sample. Density and specific surface area evolved alike, while the fabric showed a different evolution between the two samples. The undisturbed snow evolved from a weak single-maximum fabric towards a weak girdle fabric, while the sieved sample showed no evolution. The undisturbed snow sample converged toward the sieved sample fabric after 6 weeks, but continued its evolution thereafter. We suggest that the main factor causing this different behavior is the difference in density and in pore size.