CAREER: Identifying the Dominant Controls on Strain Localization in the Lower Crust

职业：确定下地壳应变定位的主要控制因素

• 批准号: 1150438
• 负责人: Christopher Gerbi
• 金额: $ 43.27万
• 依托单位: University of Maine
• 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: 2012-04-15 至 2018-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1150438&HistoricalAwards=false
• 关键词: CAREER; Identifying; Dominant; Controls; Strain

This project combines a study of crustal rheology with efforts to improve student understanding of the properties controlling the mechanical behavior of Earth materials. We integrate the two components of the project by developing a framework for university faculty, K-12 teachers, and graduate students in both Earth sciences and education to collaborate during field-based research and classroom resource development.The distribution of rock strength in the crust is a fundamental control on strain and corollary processes such as fluid flow, topographic evolution, and seismicity. Without being able to accurately characterize the strength distribution, we cannot accurately predict how the crust will respond to internal and external driving forces. Despite recent progress constraining the general mechanisms involved in strain-related weakening, we do not know which weakening processes dominate at different levels of the crust. Using the southwestern Grenville Province of Ontario, Canada, as a natural laboratory, we will combine structural, petrological, and geochronological methods, followed by analytical and numerical modeling sensitivity analysis, to determine the relative importance of different weakening mechanisms during the development of well-exposed km-scale shear zones there. We will test the following hypotheses: 1) Reaction and textural weakening are of subequal importance in shear zone development; 2) Grain size reduction is commonly not a major weakening factor at deep crustal levels; 3) Geological evidence does not require shear heating as a component in shear zone formation; and 4) Although initial heterogeneities are important for controlling the stress distribution in the crust, km-scale shear zones form due to a change in constitutive relationships. Earth's topography and the pattern of rock units exposed at the surface result almost entirely from the combination of erosion and the heterogeneous movement of rocks within the crust and mantle. In this project, we focus on identifying what controls patterns of rock movement, or deformation, in the lower portions of continental crust. By identifying the processes that control how rocks change strength during periods of mountain-building, and therefore how the lower crust accommodates the large-scale deformation induced by the movement of tectonic plates, we will improve our ability to predict and explain the evolution of Earth's surface and related processes such as fluid flow and seismicity. The physical controls on the mechanical properties of geological materials are well known. Yet many students still appear unsuccessful in understanding those core ideas in Earth Science courses, despite their inclusion in science standards. Moreover, due to a relative lack of formal studies, the geoscience community has not developed a full picture of student misconceptions and effective pedagogical strategies related to those concepts. To address this, we will use a concept inventory approach to identify student needs at the 6th-9th grade and introductory college levels in physical science content areas that underlie concepts related to deformation, then develop, implement, and evaluate the impact of instructional resources that address those needs. The principles that govern rock deformation are the same as those that govern the deformation of ice, metals, ceramics, and composite materials. Thus, students will be able to apply gains in their understanding derived from this project more broadly to fields such as glaciology and mechanical engineering. We will use the vertical integration of students, pre- and in-service K-12 teachers, and faculty as a pathway to improve student attitudes to science and engineering and to assist pre- and in-service teachers in maintaining currency in research-driven advances in the geosciences and geoscience education.

这个项目结合了地壳流变学的研究，努力提高学生对控制地球材料力学行为的性质的理解。我们通过为大学教师、K-12教师和地球科学和教育领域的研究生开发一个框架来整合项目的两个组成部分，以便在基于实地的研究和课堂资源开发期间进行合作。地壳中岩石强度的分布是对应变和必然过程（如流体流动、地形演化和地震活动）的基本控制。如果不能准确地描述强度分布，我们就无法准确地预测地壳将如何对内部和外部驱动力作出反应。尽管最近的进展限制了应变相关弱化的一般机制，但我们不知道在地壳的不同层面上，哪种弱化过程占主导地位。使用西南格伦维尔省的安大略，加拿大，作为一个天然实验室，我们将结合联合收割机结构，岩石学和地质年代学的方法，其次是分析和数值模拟的敏感性分析，以确定不同的弱化机制的相对重要性，在发展过程中暴露良好的公里级剪切带。我们将检验以下假设：（1）反应和结构弱化在剪切带发展中具有同等重要性;（2）在地壳深部，粒度减小通常不是主要的弱化因素;（3）地质证据不要求剪切加热作为剪切带形成的一个组成部分;虽然初始不均匀性对控制地壳应力分布很重要，但由于本构关系的改变，形成了公里级剪切带。地球的地形和岩石单元暴露在地表的模式几乎完全是侵蚀和地壳和地幔内岩石的不均匀运动的结果。在这个项目中，我们的重点是确定是什么控制了大陆地壳下部的岩石运动或变形模式。通过确定控制岩石在造山期间如何改变强度的过程，以及下地壳如何适应构造板块运动引起的大规模变形，我们将提高预测和解释地球表面演变和相关过程（如流体流动和地震活动）的能力。地质材料力学性质的物理控制是众所周知的。然而，许多学生似乎仍然无法理解地球科学课程中的这些核心思想，尽管它们已列入科学标准。此外，由于相对缺乏正式的研究，地球科学界尚未全面了解学生的错误概念和与这些概念有关的有效教学战略。为了解决这个问题，我们将使用一个概念库存的方法来确定学生的需求在6 - 9年级和入门大学水平的物理科学内容领域的基础概念与变形，然后开发，实施和评估的教学资源，解决这些需求的影响。控制岩石变形的原理与控制冰、金属、陶瓷和复合材料变形的原理相同。因此，学生将能够将他们从该项目中获得的理解更广泛地应用于冰川学和机械工程等领域。我们将利用学生，职前和在职K-12教师和教师的垂直整合作为改善学生对科学和工程的态度的途径，并协助职前和在职教师保持货币在地球科学和地球科学教育的研究驱动的进步。