An experimental baseline for ice-till strain indicators
An experimental baseline for ice-till strain indicators
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冰耕应变指示器的实验基线
DOI：
10.1139/cjes-2022-0074
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发表时间：
2023
影响因子：
1.4
通讯作者：
Lord, N.
中科院分区：
文献类型：
--
作者：
Zoet, L.K.;Hansen, D.D.;Morgan-Witts, N.;Menzies, J.;Sobol, P.;Lord, N.
冰下冰碛物可以变形时，覆盖冰施加剪切牵引力在冰-冰碛物界面。这种变形在冰碛物中留下了应变信号，使冰流方向上的颗粒对齐，并产生了一系列诊断性的微观结构。限制产生这些运动学指标的条件是解释基底冰碛物沉积中发现的无数特征的关键。在这里，我们使用了一个低温环剪切装置与透明的样品室壁滑一圈温和的冰在冰碛床，我们检查了应变签名在冰碛。我们使用安装在环剪侧面的摄像机和插入到冰碛层中的珠串来估计冰碛层内的应变分布。实验完成后，我们提取和分析磁化率（AMS）样品的各向异性，并创建薄切片的冰碛层的微观结构分析。然后，我们比较了AMS和微观结构与所观察到的应变历史，以检查运动学指标和应变之间的关系，在设置剪切牵引力是由冰提供。我们发现，AMS面料表现出高度的集群在高应变区域附近的冰，直到界面。在冰碛物的最上部区域，k1特征向量的方位角一般与冰流一致，S1特征值较高。然而，S1特征值和k1特征向量与冰流的对齐度随着距冰-冰碛物界面的距离而非线性地减小。在变形增加的区域中，微剪切的发生率较高。
Subglacial till can deform when overriding ice exerts shear traction at the ice–till interface. This deformation leaves a strain signature in the till, aligning grains in the direction of ice flow and producing a range of diagnostic microstructures. Constraining the conditions that produce these kinematic indicators is key to interpreting the myriad of features found in basal till deposits. Here, we used a cryogenic ring shear device with transparent sample chamber walls to slip a ring of temperate ice over a till bed from which we examined the strain signature in the till. We used cameras mounted to the side of the ring shear and bead strings inserted in the till to estimate the strain distribution within the till layer. Following the completion of the experiment, we extracted and analyzed anisotropy of magnetic susceptibility (AMS) samples and created thin sections of the till bed for microstructure analysis. We then compared the AMS and microstructures with the observed strain history to examine the relationship between kinematic indicators and strain in a setting where shear traction is supplied by ice. We found that AMS fabrics show a high degree of clustering in regions of high strain near the ice–till interface. In the uppermost zone of till,k1eigenvector azimuths are generally aligned with ice flow, andS1eigenvalues are high. However,S1eigenvalues and the alignment of thek1eigenvector with ice flow decrease nonlinearly with distance from the ice–till interface. There is a high occurrence of microshears in the zone of increased deformation.