Mechanics of Folding in Glaciers: A Numerical Study

冰川的褶皱破坏了地层分层，改变了冰和夹带在其中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，在冰川边缘特别明显，在那里含有沉积物带的冰经历了纵向压缩。虽然在这种情况下对褶皱的描述很多，但对产生褶皱的机械条件缺乏完整的了解。一种常见的假设是，当冰川通过均匀的应力场时，冰层会被动变形。然而，冰-沉积物混合物的力学性质与清洁冰有很大的不同，这表明应力应该远远不均匀。由此导致的不均匀应变，以及沉积物的输送路径，可以由含沉积物的冰和周围清洁冰之间的流变学差异来决定。该项目将使用已建立的富含沉积物的冰和清洁冰的流变学公式，评估机械不均匀冰层对冰川褶皱运动学的影响。商业有限差分程序(FLAC，Itasca Consulting Group)将用于模拟与冰川环境相关的大应变的变形。关键结果将与现有的分析和数值解决方案进行检验。该项目将为解释含有沉积层的冰川褶皱提供一个物理上有根据的框架。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冰床耦合的时间或空间上的变化。更好地理解分层的、含沉积物的冰是如何对施加的压力做出反应的，将有助于更有信心地解释导致褶皱的冰川环境。这些结果还将拓宽预测冰盖中的地层分层如何受到流动干扰的基础，从而使冰芯中地层的年代测定任务变得更加复杂。此外，这项研究有助于分析岩层中的褶皱，这种褶皱发生在无法观测的较长时间跨度内，该项目将制作一个实践教学模块，将冰川过程和构造地质学结合在一起，并将在互联网上广泛提供。

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.