Collaborative Research on Till Deformation: Linking Microstructural Characteristics to Strain

Till 变形的协作研究：将微观结构特征与应变联系起来

• 批准号: 0136006
• 负责人: Neal Iverson
• 金额: $ 14.29万
• 依托单位: Iowa State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-08-01 至 2005-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0136006&HistoricalAwards=false
• 关键词: Collaborative; Research; Till; Deformation; Linking

0136006IversonThis is a collaborative proposal by Principal Investigators at Iowa State University and the Wisconsin Geological Survey. Past glaciers, including the Pleistocene ice sheets of the Northern Hemisphere, sometimes flowed unusually fast, causing ice-mass fluctuations that resulted in severe climate change and landscape modification. A leading hypothesis attributes this rapid flow to deformation of the thawed glacier substrate. Structures preserved in the sediment beds of past ice sheets can provide a time-integrated and spatially extensive record of such deformation and can be used to test this hypothesis. Microstructures are potentially the most useful indicators of deformation, because they evolve systematically and are ubiquitous, even in massive till units. Although microstructural characteristics of deformed glacier sediments have been described extensively, there have been no methodical efforts to correlate these characteristics to shear-strain magnitude. The result is that the degree of bed deformation, and hence its role in ice-sheet motion, usually cannot be inferred reliably from the geologic record. Support is being requested to study the evolution of till microstructural characteristics as a function of shear strain with a ring-shear device that deforms a large sediment specimen to high strains. The experiments will be guided by related studies in structural geology, geophysics, and soil mechanics, which indicate that shear-plane orientations, clay-particle fabric, and anisotropy of magnetic susceptibility (AMS) change systematically with sediment deformation. These microstructural characteristics will be correlated with shear strain by conducting experiments to various strains and measuring these characteristics after each test. Two basal tills with different clay-mineral fractions will be tested and the sensitivity of the results to initial consolidation and total normal stress will be studied. Shear planes will be identified optically and the extent of Y-shear development relative to shears at other orientations, an indicator of shear-strain magnitude, will be quantified. Clay-particle fabrics will be measured with an X-ray, pole-figure goniometer at the University of Michigan and quantified by computing both eigenvalues and March strains. AMS will be measured at the Institute for Rock Magnetism at the University of Minnesota and used to compute AMS magnitudes, as well as strengths and directions of fabrics defined by orientations of maximum susceptibility. These experiments will help improve models of past ice sheets and interpretations of glacigenic sediments and landforms. This research may also help solve related problems in structural geology, geophysics, petroleum geology and geotechnical engineering, in which deformation of granular media and consequent anisotropy are often central issues.

0136006iversonthis是爱荷华州立大学和威斯康星地质调查局的首席研究人员的合作提议。 过去的冰川，包括北半球的更新世冰盖，有时会异常流动，导致冰质量的波动导致严重的气候变化和景观修饰。主要的假设将这种快速的流动归因于解冻冰川底物的变形。保存在过去冰盖的沉积物床上的结构可以提供这种变形的时间集成和空间广泛的记录，并可用于检验该假设。微观结构可能是变形的最有用的指标，因为它们系统地演化并且无处不在，即使在庞大的直到单位中也是如此。尽管已广泛描述了变形冰川沉积物的微观结构特征，但没有将这些特性与剪切 - 应变幅度相关联的方法。结果是床变形的程度及其在冰页运动中的作用，通常无法从地质记录中可靠地推断出来。 正在要求使用环形剪切装置将直到微结构特性的演变作为剪切应变的函数，该剪切设备将大型沉积物标本变形为高应变。 实验将以结构地质，地球物理学和土壤力学的相关研究为指导，这些研究表明磁敏感性（AMS）随着沉积物变形而系统地改变了剪切平面方向，粘土晶体织物和各向异性。这些微观结构特性将通过对各种菌株进行实验并在每次测试后测量这些特征来与剪切应变相关。将测试两个具有不同粘土阵线分数的基础耕作，并将研究结果对初始固结的敏感性和总正应力。剪切平面将在光学上识别，并且将对其他方向相对于剪切的Y剪切发育的程度（将剪切 - 应变幅度的指标）进行量化。粘土粒子织物将以密歇根大学的X射线，杆位角度计测量，并通过计算特征值和3月份菌株来量化。 AMS将在明尼苏达大学的岩石磁化研究所进行测量，并用于计算AMS幅度，以及由最大易感性的方向定义的织物的优势和方向。这些实验将有助于改善过去的冰盖模型以及对冰川沉积物和地形的解释。这项研究还可能有助于解决结构地质，地球物理学，石油地质和岩土工程方面的相关问题，其中颗粒介质的变形以及随之而来的各向异性通常是核心问题。