Quantifying Syntectonic Weakening in Deep Orogenic Crust

量化深造山地壳的同构造弱化

• 批准号: 0837922
• 负责人: Christopher Gerbi
• 金额: $ 23.87万
• 依托单位: University of Maine
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-08-01 至 2013-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0837922&HistoricalAwards=false
• 关键词: Quantifying; Syntectonic; Weakening; Deep; Orogenic

The primary intellectual impact of this project will be in improving our understanding of the mechanics that shape the Earth's crust. In recent years, earth scientists have used the increasing body of geodetic data towards that end, but the mechanical properties of the middle and lower crust remain only loosely constrained. This project focuses on the magnitude of strain weakening in shear zone networks. In detail, the research will explore the grain-scale and outcrop-scale deformation mechanisms in minerals that lead to this weakening, followed by modeling of the results to understand the weakening process on the larger scale. These conceptual and numerical models will allow better prediction of where and how fast the continental crust will deform and in turn this will benefit society. In the future, locations that have recently been deglaciated, and those in tectonically active areas where earthquakes are likely, may be interesting targets for further application of this research. This project also serves as a vehicle to continue and enhance ongoing educational and outreach initiatives at the K-16 and graduate levels. Support for students enrolled in the University of Maine's Master of Science in Teaching program will allow pre-service K-12 teachers to become involved in an active research project and to participate in creating an environment where science is more accessible. The PI and colleagues will develop new content based around supercomputer, visualization, and field video library projects, the combined results of which will enhance professional development, graduate and undergraduate courses, and outreach to K-12 students in Maine's rural areas.Throughout the lithosphere, strain localization plays a fundamental role in tectonic processes affecting, for example, seismicity, exhumation, fluid migration and mineralization, magma transport, and topographic and plate boundary evolution. Previous research involving field observations and numerical modeling has produced many constraints on the causes and consequences of strain localization, but researchers lack a thorough understanding of the magnitude of strength variation in the deep crust in particular. Due to exceptional exposure and deep exhumation this research group will use the Parry Sound domain of the Grenville Province, southern Ontario, as a natural laboratory. Along one margin of the domain, granulite facies mineral assemblages have been transformed under upper amphibolite facies conditions along meter-scale shear zones. After field-based mapping, the PI will quantify the change in strength associated with the development of the interconnected meter-scale shear zones through model calculations using the natural geometric framework. In addition, to develop better tools to predict weakening of this magnitude elsewhere, he will determine the mechanisms by which the shear zones developed and the weakening occurred. The PI has hypothesized that one such mechanism involved pegmatite-derived fluids that infiltrated adjacent zones, allowing mineralogical changes along which shear zones could nucleate. Establishing the crustal-scale significance of strength changes requires determining if meter-scale processes produced, for example, the regional-scale, domain-bounding Twelve Mile Bay shear zone. Preliminary observations indicate that fractures with no lateral offset assisted full transposition of the fabric as they evolved into interconnected meter-scale shear zones during progressive deformation. This research group will evaluate whether these preliminary interpretations are valid through the mapping of thermobarometric and geochronologic patterns along the inferred length of the Twelve Mile Bay shear zone.

这个项目的主要智力影响将是提高我们对塑造地壳的力学的理解。 近年来，地球科学家利用越来越多的大地测量数据来实现这一目标，但中地壳和下地壳的力学性质仍然只是受到松散的限制。 本项目的重点是剪切带网络中应变弱化的大小。 详细地说，该研究将探索导致这种弱化的矿物中的颗粒尺度和露头尺度变形机制，然后对结果进行建模，以了解更大尺度上的弱化过程。 这些概念和数值模型将有助于更好地预测大陆地壳将在何处以及以多快的速度变形，这反过来将造福于社会。 在未来，最近被冰川消融的地点，以及那些可能发生地震的构造活跃地区，可能是这项研究进一步应用的有趣目标。 该项目还作为一种工具，继续和加强正在进行的教育和推广活动，在K-16和研究生水平。 对就读于缅因州大学教学科学硕士课程的学生的支持将允许职前K-12教师参与积极的研究项目，并参与创造一个更容易获得科学的环境。 PI和同事们将围绕超级计算机、可视化和现场视频库项目开发新内容，其综合成果将促进专业发展、研究生和本科生课程，以及对缅因州农村地区K-12学生的推广。在整个岩石圈中，应变局部化在影响地震活动、折返、流体运移与成矿作用、岩浆运移、地形与板块边界演化。 以往涉及现场观测和数值模拟的研究对应变局部化的原因和后果产生了许多限制，但研究人员对特别是地壳深部强度变化的幅度缺乏透彻的了解。 由于特殊的暴露和深度挖掘，该研究小组将使用安大略南部格伦维尔省的帕里湾域作为天然实验室。 在该构造域的沿着一侧边缘，麻粒岩相矿物组合在上角闪岩相条件下发生了沿着米级剪切带的转变。 在基于实地的测绘之后，PI将通过使用自然几何框架的模型计算来量化与互连的米级剪切区的发展相关的强度变化。 此外，为了开发更好的工具来预测其他地方的这种强度的弱化，他将确定剪切带发展和弱化发生的机制。 PI假设，其中一种机制涉及伟晶岩衍生的流体渗入相邻区域，从而允许矿物学变化沿着剪切带成核。 确定强度变化的地壳尺度意义需要确定米级过程是否产生了区域尺度的、以区域为边界的十二里湾剪切带。 初步观察表明，没有侧向偏移的断裂有助于组构的完全移位，因为它们在渐进变形过程中演变成相互连接的米级剪切区。 该研究小组将通过绘制沿沿着十二里湾剪切带推断长度的温压和地质年代模式图，评估这些初步解释是否有效。