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Cooling During Deformation: An Overlooked Scenario with Implications for the Analysis of Ductily Deformed Rocks

变形过程中的冷却：一个被忽视的场景，对延展性变形岩石的分析具有重要意义

基本信息

批准号：
1951142
负责人：
Steven Kidder
金额：
$ 38.29万
依托单位：
CUNY City College
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2020
资助国家：
美国
起止时间：
2020-07-01 至 2024-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1951142&HistoricalAwards=false
关键词：
Cooling During Deformation Overlooked Scenario

项目摘要

The spatial and temporal variability of stress magnitudes in Earth’s crust are active and longstanding research areas in several branches of the geosciences, e.g. geodynamics and earthquake mechanics. This study investigates a widely used tool which relates grain size of rock samples to stress levels by conducting a series of experiments in which rocks are cooled as they are deformed, mimicking the cooling of natural rocks as they are carried by faults towards Earth’s surface. The project explores the possibility that the statistics of grain size distributions in such samples can be used to extract useful information about the stress and deformation history of such rocks. The project is advancing desired societal outcomes through: (1) improved understanding of processes involved in earthquakes; (2) full participation of women and underrepresented minorities in science, technology, engineering and mathematics (STEM); and (3) the development of a diverse, globally competitive STEM workforce through training of graduate and undergraduate students from underrepresented groups in the Earth sciences and support of two early career scientists.The recrystallized grain size of rocks deformed in the middle crust is routinely used to constrain differential stress magnitudes and rock rheology. Such “grain size piezometry” requires an assumption of microstructural steady state, however most exposed ductile shear zones experienced deformation while cooling. Cooling causes an increase in rock strength, and as a result, a stable recrystallized grain size is a moving target. Recent rock deformation experiments demonstrate that, at ratios of cooling rate to strain rate equivalent to those of typical natural shear zones, recrystallized grain size is markedly out of equilibrium—recrystallized grain sizes are twice as large as would occur if a steady-state were achieved. This result motivates the primary goals of this proposal: 1) determine robust criteria for recognizing microstructures that are affected by cooling during deformation, and 2) develop a toolkit for constraining stress histories from such rocks. Preliminary work on goal one demonstrates that there are systematic differences in the shapes of grain size distributions of cooling ramp experiments versus experiments at constant temperature. A suite of Griggs Rig, general-shear cooling-ramp experiments over a 500°C range of temperature are conducted. These experiments will--in conjunction with Electron backscatter diffraction (EBSD) scanning electron microscopy data from well-constrained natural samples and archival experiments carried out at constant temperature—explore extrapolation of laboratory results to low temperature geologic conditions, and potential effects of strain, initial grain size, and the presence of porphyroclasts and secondary phases.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

地壳应力强度的时空变化是地球动力学和地震力学等多个地球科学分支长期活跃的研究领域。这项研究调查了一种广泛使用的工具，该工具通过进行一系列实验将岩石样品的粒度与应力水平联系起来，在这些实验中，岩石在变形时被冷却，模仿天然岩石在断层带向地球表面时的冷却。该项目探讨了这样的样品中的粒度分布的统计数据可以用来提取有关这些岩石的应力和变形历史的有用信息的可能性。该项目正在通过以下方式推进预期的社会成果：（1）提高对地震过程的认识;（2）妇女和代表性不足的少数群体充分参与科学、技术、工程和数学;（3）发展多样化的，通过培训来自地球科学领域代表性不足群体的研究生和本科生，早期职业科学家。在中地壳变形的岩石的重结晶粒度通常用于限制差应力大小和岩石流变学。这种“粒度测压法”需要一个假设的微观结构稳定状态，但大多数暴露的韧性剪切带经历变形，而冷却。冷却导致岩石强度增加，因此，稳定的再结晶晶粒尺寸是一个移动的目标。最近的岩石变形实验表明，在冷却速率与应变速率之比相当于那些典型的自然剪切带，再结晶晶粒尺寸是显着的平衡再结晶晶粒尺寸的两倍大，如果达到稳态。这一结果激发了本提案的主要目标：1）确定识别变形过程中受冷却影响的微观结构的可靠标准，以及2）开发用于约束此类岩石应力历史的工具包。目标一的初步工作表明，有系统的差异，在形状的晶粒尺寸分布的冷却斜坡实验与恒温实验。在500°C的温度范围内进行一套Griggs Rig通用剪切冷却斜坡实验。这些实验将结合来自约束良好的天然样品的电子背散射衍射（EBSD）扫描电子显微镜数据和在恒温下进行的档案实验，探索实验室结果对低温地质条件的外推，以及应变、初始晶粒尺寸、该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的评估来支持。影响审查标准。