Mechanics of Folding in Glaciers: A Numerical Study

冰川折叠机制：数值研究

• 批准号: 1024264
• 负责人: Peter Moore
• 金额: $ 4.86万
• 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: 2010
• 资助国家: 美国
• 起止时间: 2010-08-01 至 2012-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1024264&HistoricalAwards=false
• 关键词: Mechanics; Folding; Glaciers; Numerical; Study

Folding in glaciers disrupts stratigraphic layering and changes flow trajectories of ice and any sediment entrained therein. Folds appear at scales ranging from centimeters to hundreds of meters, and are particularly evident near glacier margins where ice containing sediment bands undergoes longitudinal compression. While descriptions of folds in this context are plentiful, a complete understanding of the mechanical conditions that produce them is lacking. A common assumption is that layers become distorted passively as the glacier passes through homogeneous stress fields. However, ice-sediment mixtures have significantly different mechanical properties than clean ice, suggesting that stresses should be far from homogeneous. Resulting inhomogeneous strains, and therefore sediment transport paths, can be dictated by the rheological differences between sediment-bearing ice and surrounding clean ice. This project will evaluate the impact of mechanically inhomogeneous ice layering on fold kinematics in glaciers using established rheological formulations for sediment-rich ice and clean ice. A commercial finite difference code (FLAC, Itasca Consulting Group) will be used to simulate deformation to large strains relevant in glacial environments. Key results will tested against available analytical and numerical solutions.This project will provide a physically-grounded framework for interpretation of folds in glaciers containing sediment layers. Folded layers preserve a composite record of the stresses experienced by the ice as it passes through the glacier. Changes in stresses are often due to temporal or spatial changes in the glacier's coupling to the bed. A better understanding of how layered, sediment-bearing ice responds to imposed stresses will allow more confident interpretation of the glaciological circumstances that gives rise to folds. The results will also broaden the basis for prediction of how stratigraphic layering in ice sheets can be disturbed along flow, complicating the task of dating layers in ice cores. Furthermore, the study can contribute to the analysis of folding in rock formations, which occur over longer time spans that cannot be observed, This project will produce a hands-on teaching module integrating glacial processes and structural geology that will be made widely available on the internet.

冰川的折叠破坏了地层分层并改变了冰和其中夹带的任何沉积物的流动轨迹。褶皱的规模从厘米到数百米不等，在冰川边缘附近尤其明显，其中含有沉积物的冰遭受纵向压缩。虽然在这方面对褶皱的描述很多，但缺乏对产生褶皱的机械条件的完整理解。 一个常见的假设是，当冰川穿过均匀应力场时，各层会被动变形。然而，冰-沉积物混合物的机械性能与干净的冰显着不同，这表明应力应该远非均匀。由此产生的不均匀应变以及沉积物传输路径可以由含有沉积物的冰与周围干净冰之间的流变学差异决定。该项目将使用针对富含沉积物的冰和清洁冰的既定流变学公式来评估机械不均匀冰层对冰川褶皱运动学的影响。商业有限差分代码（FLAC，Itasca Consulting Group）将用于模拟冰川环境中相关大应变的变形。主要结果将根据可用的分析和数值解决方案进行测试。该项目将为解释含有沉积物层的冰川褶皱提供一个物理基础框架。 折叠层保存了冰穿过冰川时所经历的应力的综合记录。 应力的变化通常是由于冰川与河床耦合的时间或空间变化造成的。 更好地了解分层的、含有沉积物的冰如何应对施加的压力，将有助于更自信地解释产生褶皱的冰川环境。这些结果还将拓宽预测冰原中的地层分层如何沿着流动受到干扰的基础，从而使冰芯中层的测年任务复杂化。此外，该研究有助于分析岩层的褶皱，这些褶皱发生在无法观察到的较长时间跨度内。该项目将制作一个整合冰川过程和构造地质学的实践教学模块，该模块将在互联网。