Collaborative Research: Deformation Thermometry and Water Weakening of Quartz Tectonites - Case Studies from the Himalaya and the Caledonides of NW Scotland

合作研究：石英构造岩的变形测温和水弱化——喜马拉雅山和苏格兰西北部喀里多尼亚山脉的案例研究

• 批准号: 1220345
• 负责人: Richard Law
• 金额: $ 18.4万
• 依托单位: Virginia Polytechnic Institute and State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-08-15 至 2017-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1220345&HistoricalAwards=false
• 关键词: Collaborative; Research; Deformation; Thermometry; Water

Quantitative determination of the ambient temperatures at which rocks deform under different tectonic settings in the earth's crust is of critical importance for constraining thermo-mechanical modeling of the earth's tectonic plates, and their mechanical and thermal evolution. Ambient deformation temperatures control the physical processes that govern deformation and the rates at which deformation occurs. Pressure-Temperature-time (PTt) histories of rocks can be obtained from the compositions of minerals and mineral assemblages, through reaction equilibrium relations, but these determinations bear on the PT conditions of the mineral reactions, not necessarily those of deformation. Development of thermometers that directly constrain conditions of deformation is important because temperatures indicated by deformation features and those indicated by equilibrium mineral assemblages may differ, recording different intervals of a rock's PTt history. In quartz-rich continental crust, two types of deformation thermometers (based on quartz recrystallization processes and crystallographic fabrics) have been used as analytical tools over the last two decades in a wide range of tectonic studies, assuming that temperature is the primary controlling factor in recrystallization regime and fabric development. However, recrystallization regimes and fabric development may also be influenced by trace levels of water, and the effects of water on deformation mechanisms and fabric development may be of comparable importance to temperature. We propose to test, refine, and validate the deformation thermometers for quartz-bearing rocks and to examine those conditions under which water contents or variations in deformation rate need to be evaluated. We have chosen Himalayan and NW Scotland field areas as case studies because one of us has already collected extensive suites of appropriate oriented quartz-rich tectonites from these areas under prior NSF funding. These samples have been deformed under a wide range of tectonic settings and deformation thermometry, together with more restricted compositionally based thermometry, have already been completed on many of these samples. Deformation temperatures indicated by recrystallization regime and crystallographic fabrics in individual samples will be independently compared/tested by titanium-in-quartz thermometry, while the potential influence of water on recrystallization and crystallographic fabrics will be investigated by infrared spectroscopy and transmission electron microscopy. Integration of theoretical concepts and analytical techniques developed in Geosciences and Materials Science over the last half century has led to major advances in our understanding of both the mechanisms by which rocks deform/flow and the influence of environmental factors such as temperature on flow in the earth's crust. However the most commonly applied analytical techniques for determining the temperatures at which rocks now exposed at the earth's surface have been deformed are known to also be sensitive to fluctuations in chemically-induced weakening that may have occurred during deformation in the mineral grains making up the rock. Thus, deformation temperatures calculated using these thermometers may be in error, and thermomechanical numerical models developed to simulate flow in the crust using such temperature data may give unrealistic results. This project is designed to test the validity of these thermometers using a recently developed thermometer that takes such chemical processes in to account. Rock samples collected under previous NSF funding from ancient mountain belts in the Himalaya and Scotland have been chosen as case studies, and the potential role of chemical weakening in these samples will also be evaluated using complementary analytical techniques. These studies have important applications to plate tectonics and the results may change our understanding of the mechanical and thermal character of plates. Plate thickness and strength were originally considered to be due solely to temperature and the geothermal gradient in the earth. Our study addresses this concept and tests whether the internal strength of plates may also be influenced by water content, in addition to temperature. The project is a collaborative effort between researchers at Virginia Tech, Texas A&M University and Rensselaer Polytechnic Institute. In addition to the scientific goals of the project, this research is contributing to the training of Ph.D. students at Virginia Tech and Texas A&M, and providing support for an early career post-doctoral researcher at RPI. Undergraduate students at all of the participating institutions will be involved in the research.

定量确定在地壳中不同构造环境下岩石变形的环境温度对于约束地球构造板的热机械建模以及它们的机械和热进化至关重要。 环境变形温度控制着控制变形的物理过程和发生变形的速率。 可以通过反应平衡关系从矿物质和矿物质组合的组成中获得岩石的压力温度（PTT）历史，但是这些确定在矿物反应的PT条件下，不一定是变形。 直接限制变形条件的温度计的开发很重要，因为变形特征指示的温度和平衡矿物组合所指示的温度可能会有所不同，从而记录了岩石PTT历史的不同间隔。在富含石英的大陆壳中，在过去的二十年中，在广泛的构造研究中，两种类型的变形温度计（基于石英再结晶过程和晶体织物）被用作分析工具，因为假设温度是重结晶方案和织物发育中温度的主要控制因子。 但是，再结晶状态和织物发育也可能受到痕量水平的影响，水对变形机制和织物发育的影响可能与温度相当。我们建议测试，完善和验证含石英岩石的变形温度计，并检查需要评估水含量或变形速率变化的条件。我们选择了喜马拉雅和西北苏格兰现场区域作为案例研究，因为我们中的一个人已经在以前的NSF资金下从这些地区收集了广泛的适合定向的石英构造构造的套件。 这些样品在广泛的构造设置和变形温度计下已变形，以及更受限制的基于构图的温度计，已经在许多这些样品上完成了。 通过重结晶状态指示的变形温度和各个样品中的晶体织物将通过钛合金列克斯体温进行独立比较/测试，而水对再结晶和晶体学织物的潜在影响将通过红外光谱和传输电子显微镜进行研究。过去半个世纪中地球科学和材料科学中开发的理论概念和分析技术的整合使我们对岩石变形/流动的机制以及环境因素（例如温度对地球壳中流动的影响）的影响有了重大进展。 但是，已知最常用的分析技术用于确定现在暴露在地球表面的岩石变形的温度也对化学诱导的弱化的波动也很敏感，而化学诱导的弱化的衰弱可能在矿物谷物中可能发生的岩石变形时可能发生。 因此，使用这些温度计计算得出的变形温度可能是错误的，并且开发了用于使用此类温度数据模拟地壳中流动的热机械数值模型可能会产生不切实际的结果。 该项目旨在使用最近开发的温度计测试这些温度计的有效性，该温度计将这种化学过程考虑在内。 在喜马拉雅山脉和苏格兰的古老山带以前的NSF资助下收集的岩石样品已被选为案例研究，化学削弱在这些样品中的潜在作用也将使用互补的分析技术进行评估。 这些研究在板块构造方面具有重要的应用，结果可能会改变我们对板的机械和热特征的理解。 板厚度和强度最初被认为仅是由于温度和地球中的地热梯度造成的。 我们的研究解决了这一概念，并测试了板的内部强度是否还可能受水含量的影响，除了温度。该项目是弗吉尼亚理工大学，德克萨斯A＆M大学的研究人员与伦斯勒理工学院研究所之间的合作努力。除了该项目的科学目标外，这项研究还为博士学位的培训做出了贡献。 Virginia Tech和Texas A＆M的学生，为RPI的早期职业生涯后研究人员提供支持。所有参与机构的本科生将参与研究。