Field and microstructural investigation of strain localization processes, texture development, and the rheology of naturally deformed lower crust

应变局部化过程、纹理发展和自然变形下地壳流变学的现场和微观结构研究

• 批准号: 1808117
• 负责人: Seth Kruckenberg
• 金额: $ 31.26万
• 依托单位: Boston College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-06-15 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1808117&HistoricalAwards=false
• 关键词: Field; microstructural; investigation; strain; localization

The rheology (i.e. the deformational behavior) of Earth's crust and upper mantle exerts a fundamental control on a range of planetary processes, from accurately modeling plate tectonics, to estimating patterns of post-glacial rebound and the propagation of seismic deformation. Models of sea level rise are similarly influenced by our understanding of the viscosity structure of the crust and upper mantle, having direct consequences for humans in coastal communities that base their future planning and development on model predictions. Thus, our ability to accurately predict the societal effects of global and local sea level change is, in part, dependent upon a nuanced understanding of the conditions and processes that control the deformational behavior of Earth materials. This study will produce empirical estimates of rheology from some of the least accessible, and least understood, deep crustal materials, thus informing on various model inputs and global processes. Teaching and training of graduate and undergraduate students are cornerstones of the integrated research efforts outlined in this study, with a particular focus on the participation of women in international STEM (Science, Technology, Engineering and Mathematics) research experiences. This study further aims to leverage the development of new digital databases and scientific tools (e.g., the StraboSpot database for structural analysis) to facilitate the free dissemination of primary data and scientific findings, and it seeks to develop new tools used for the characterization of crystalline solids, offering potential for technology transfer and breakthroughs in other STEM fields. The viscous rheologies of many minerals (e.g., olivine, quartz) and mineral aggregates (e.g., olivine and orthopyroxene) in the lithosphere have been studied for some time, yet rheologies for polyphase aggregates (e.g., gabbro -- the dominant lithology comprising the lower crust) remain poorly constrained. Because plagioclase and pyroxene are among the most common minerals in the lower crust, investigating the micromechanical processes that govern their deformation is fundamental to advancing the understanding of a range of geodynamic processes, particularly in active orogenic settings where the ability to make tectonic inferences from indirect methods of observation rests upon knowledge as to the origin of structural fabrics and crystallographic textures developed during high-temperature viscous flow. Rheological information obtained from field-based and microstructural investigations of exhumed deep crustal lithospheric sections thus remain critical as these exposures record within them the rock microstructures, deformation mechanisms, and crystallographic textures formed in the deep crust during deformation under natural conditions. This research focuses on naturally deformed, compositionally heterogeneous deep crustal granulite exposures in the Mount Hay block of central Australia and is rooted in field-based investigation, and integrated with microstructural studies, strain analysis, and textural analysis using electron backscatter diffraction. Using these methods, this research will provide quantitative constraints on: (i) deformation heterogeneity and strain localization processes in the deep crust; (ii) the compositional and tectonic controls the micromechanics of deformation in polyphase aggregates; and (iii) the rheology of heterogeneous lower crustal lithologies. Further, this study aims to explore the role of strain geometry on the development of crystallographic preferred orientation (CPO) in plagioclase-dominated rocks (e.g., gabbro), offering immense potential for improving the interpretation of lithospheric processes that depend on fabric anisotropy (e.g., seismic anisotropy, viscous anisotropy, melt percolation).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.

地壳和上地幔的流变学（即变形行为）对一系列行星过程施加基本控制，从精确建模板块构造，到估计冰后期反弹和地震变形传播的模式。海平面上升的模型同样受到我们对地壳和上地幔粘性结构的理解的影响，对沿海社区的人类产生直接影响，这些社区的未来规划和发展都基于模型预测。因此，我们准确预测全球和局部海平面变化的社会影响的能力，部分取决于对控制地球物质变形行为的条件和过程的细致入微的理解。这项研究将从一些最不容易获得，最不了解的深层地壳材料中产生流变学的经验估计，从而为各种模型输入和全球过程提供信息。研究生和本科生的教学和培训是本研究报告中概述的综合研究工作的基石，特别关注妇女参与国际STEM（科学、技术、工程和数学）研究经验。本研究还旨在利用新的数字数据库和科学工具的开发（例如，StraboSpot结构分析数据库），以促进原始数据和科学发现的自由传播，并寻求开发用于晶体固体表征的新工具，为其他STEM领域的技术转让和突破提供潜力。许多矿物的粘性流变性（例如，橄榄石，石英）和矿物聚集体（例如，橄榄石和斜方辉石）已经研究了一段时间，但是多相聚集体的流变学（例如，辉长岩----构成下地壳的主要岩性）仍然缺乏约束。由于斜长石和辉石是下地壳中最常见的矿物之一，因此研究控制其变形的微观力学过程对于促进对一系列地球动力学过程的理解至关重要，特别是在活跃的造山环境中，从间接观察方法进行构造推断的能力取决于对高-温度粘性流动。因此，从基于实地和微观结构的调查中获得的流变学信息仍然是至关重要的，因为这些暴露记录了岩石的微观结构，变形机制和在自然条件下变形过程中形成的地壳深部的晶体结构。本研究的重点是自然变形，成分不均匀的地壳深部麻粒岩暴露在中部澳大利亚的海伊山块，植根于实地调查，并结合显微结构研究，应变分析，和纹理分析，电子背散射衍射。使用这些方法，这项研究将提供定量约束：（一）变形的不均匀性和应变局部化过程中的地壳深部;（二）组成和构造控制变形的微观力学在多相聚集体;和（三）流变学的非均质下地壳岩性。此外，本研究旨在探索应变几何形状对斜长石为主的岩石（例如，辉长岩），为改善依赖于组构各向异性的岩石圈过程的解释提供了巨大潜力（例如，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。