Collaborative Research: The Role of Rock Composition and Microstructural Evolution on Strain Localization and the Effective Viscosity of the Crust

合作研究：岩石成分和微观结构演化对应变局部化和地壳有效粘度的作用

• 批准号: 1624178
• 负责人: James Hirth
• 金额: $ 20.79万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-01 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1624178&HistoricalAwards=false
• 关键词: Collaborative; Research; Role; Rock; Composition

Knowledge of the controls on the mechanical behavior of the continental crust is a fundamental underpinning for understanding a wide range of geological processes. For example, the long-term flow of crustal materials at depth controls how the crust deforms due to loading or unloading associated with sea level rise and fall, glacial advance and retreat, and mountain building and erosion. Deformation of the Earth's surface before and after large earthquakes is also controlled by the mechanical behavior of crustal rocks. Scientists have long used knowledge of the mechanical properties of the continental crust's constituent minerals to estimate how the crust should respond but, surprisingly, little is known about how aggregates of these minerals (rocks) respond. A research team from Brown University and Woods Hole Oceanographic Institution, in collaboration with scientists from Norway and New Zealand, aims to develop a better understanding of how crustal rocks flow under high temperature and pressure when subjected to external stresses. They will deform crustal materials in the laboratory and carry out computer modeling to improve understanding of the flow of crustal materials under both short-term (earthquakes) and long-term (mountain belts) loads. The research project additionally advances desired societal outcomes through the development of a diverse, globally competitive STEM workforce by training graduate and undergraduate training in laboratory experiments and numerical modeling.This project will acquire new experimental and microstructural data and conduct modeling studies of deformation in crustal multi-phase rocks to investigate the rheological properties of the continental crust, with emphasis on the effects of composition and strain localization. The experiments and microstructural observations focus on quartz+garnet, quartz+muscovite, and quartz+albite systems in order to improve understanding of crustal rheology and the role of grain size sensitive creep in the formation and rheology of shear zones. The research team finds that combining rheological mixing models (incorporating single-phase flow laws) with calculations of stable mineral assemblages is a promising way to investigate the role of rock composition on crustal viscosity. Agreement between such models and geodetic observations is encouraging, however, there are several limitations to this approach that this research will address: (1) garnet flow laws predict widely varying viscosities at crustal conditions, severely hampering the potential for relating seismic properties to rheology; (2) existing flow laws for mica aggregates and mica single crystals also predict widely different strengths at crustal conditions, primarily due to uncertainties related to the influence of mica content and strain rate; (3) shear zone formation processes, which are neglected in the mixing models, appear to produce microstructures in which the grain size of the mixed layers is set by Zener pinning; and (4) recent experimental work is suggestive of grain size sensitive creep and grain boundary sliding in quartz aggregates. Experiments will be conducted using Griggs apparatus at 700?1100 degrees C and strain rates from 3e-7/s to 1e-4/s at confining pressures from 0.8 to 2.0 GPa. To compliment the interpretation of the experimental data, the researchers will conduct numerical simulations of grain size evolution and shear zone development in polyphase rocks. Models will investigate shear zone evolution in isotropic, homogeneous systems and 2-D shear zone development in heterogeneous systems where local variations in stress can influence grain-size evolution in both the strong and weak phases.

了解控制大陆地壳机械行为的控制是理解广泛地质过程的基本基础。例如，在深度处的地壳材料的长期流动控制着与海平面上升和下降，冰川前进和撤退以及山区建筑和侵蚀相关的负载或卸载引起的地壳变形。大地震前后地球表面的变形也由地壳岩石的机械行为控制。长期以来，科学家已经对大陆壳矿物质的机械性能进行了了解，以估计外壳应如何反应，但令人惊讶的是，这些矿物质（岩石）的响应方式鲜为人知。布朗大学和伍兹霍尔海洋学机构的研究团队与挪威和新西兰的科学家合作，旨在更好地理解地壳在高温下如何在高温和压力下遇到外部压力时如何流动。它们将在实验室中变形地壳材料，并进行计算机建模，以提高对短期（地震）和长期（山带）负载下地壳材料流动的理解。研究项目还通过培训研究生和实验室实验和数值建模的培训研究生和本科培训来开发多样化的全球竞争性STEM劳动力，并提高所需的社会成果。该项目将获取新的实验和微观结构数据，并在Crustal Multii Multii Multii formitization and Incontional Insportional培训中 - 相岩石研究大陆地壳的流变特性，重点是组成和应变定位的影响。实验和微观结构观测集中在石英+石榴石，石英+麝香木和石英+albite系统上，以提高对地壳流变学的理解以及晶粒尺寸敏感的蠕变在剪力区域的形成和流变学中的作用。研究小组发现，将流变学混合模型（合并单相流量法则）与稳定矿物组合的计算相结合是研究岩石组成对地壳粘度的作用的一种有前途的方法。但是，这种模型与大地观察之间的一致性令人鼓舞，但是，这种研究将解决这一方法的局限性：（1）石榴石流量法预测在地壳条件下的粘度发生了巨大变化，严重阻碍了将地震特性与流变学联系起来的潜力； （2）云母骨料和云母单晶的现有流量法也预测了地壳条件下的强度截然不同，这主要是由于与云母含量和应变速率的影响有关的不确定性； （3）在混合模型中忽略的剪切带形成过程似乎会产生微观结构，其中混合层的晶粒大小由Zener固定设置； （4）最近的实验工作暗示了晶粒大小敏感的蠕变和石英骨料中的晶界滑动。实验将使用700？1100摄氏度的Griggs设备进行，并在0.8至2.0 GPa的限制压力下从3E-7/s到1E-4/S的应变速率进行实验。为了补充实验数据的解释，研究人员将对多相岩石中的晶粒尺寸演化和剪切区发育进行数值模拟。模型将研究各向同性，均质系统和二维剪切区发育的剪切区的进化，在这些系统中，压力的局部变化会影响强相和弱相的晶粒尺寸进化。