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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >The experimental basis for interpreting particle and magnetic fabrics of sheared till
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The experimental basis for interpreting particle and magnetic fabrics of sheared till

机译：解释剪切机的颗粒和磁性织物的实验基础。

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摘要

Particle fabrics of basal tills may allow testing of the bed-deformation model of glacier flow, which requires high bed shear strains (>100). Field studies, however, have not yielded a systematic relationship between shear-strain magnitude and fabric development. To isolate this relationship four basal tills and viscous putty were sheared in a ring-shear device to strains as high as 714. Fabric was characterized within a zone of shear deformation using the long-axis orientations of fine-gravel and sand particles and the anisotropy of magnetic susceptibility (AMS) of small (similar to 5-8 cm(3)) intact samples. Results indicate that till particles rotate toward the plane of shearing with long-axis orientations that become tightly clustered in the direction of shear (0.78 < S-1 < 0.94 for three-dimensional data). These strong, steady-state fabrics are attained at shear strains of 7-30, with no evidence of fabric weakening with further strain, regardless of the specific till or particle-size fraction under consideration. These results do not support the Jeffery model of particle rotation, which correctly describes particle rotation in the viscous putty but not in the tills, owing to fluid-mechanical assumptions of the model that are violated in till. The sensitivity of fabric development to shear-strain magnitude indicates that, for most till units where shear-strain magnitude is poorly known, attributing fabric variations to spatial differences in other variables, such as till thickness or water content, will be inherently speculative. Attributing fabric characteristics to particular basal till facies is uncertain because shear-strain magnitude is unlikely to be closely correlated to till facies. Weak or spatially variable fabrics, in the absence of post-depositional disturbance or major deviations from unidirectional simple shear, indicate that till has not been pervasively sheared to the high strains required by the bed-deformation model. Strong How-parallel fabrics are a necessary but insufficient criterion for confirming the model. Copyright (C) 2008 John Wiley & Sons, Ltd.
机译：基础耕作的颗粒织物可用于测试冰川流动的床层变形模型，该模型需要较高的床层剪切应变（> 100）。但是，实地研究尚未得出剪切应变幅度与织物发育之间的系统关系。为了分离这种关系，在环形剪切装置中将四个基耕和粘性腻子剪切至高达714的应变。使用细砾石和沙粒的长轴方向以及各向异性，在剪切变形区域内对织物进行表征。小（类似于5-8 cm（3））完整样本的磁化率（AMS）。结果表明，直到粒子朝着具有长轴方向的剪切平面旋转，并在剪切方向上紧密聚集（对于三维数据，其为0.78

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