Collaborative Research: An integrated evaluation of lower crustal rheology and localization processes in plagioclase-rich rocks

地壳在不同的深度通过不同的过程变形。地壳的下部很难在野外接触到，因此比上地壳了解得更少。虽然地震通常发生在上地壳，但下地壳通过将应力转移到较浅的断层来影响地震活动。利用实地研究、实验室分析和数值模型相结合的方法，该项目将评估哪些过程允许在下地壳的狭窄区域发生变形。该项目将使用加拿大魁北克省地表下部地壳形变的曝光，使我们能够直接研究岩石和变形过程。特别是，研究人员将确定与上地壳较浅的地震致震断层的相互作用是否足以解释该地区的特征，或者额外的岩石弱化过程是否发挥了根本作用。这种上、下地壳形变之间的关系对于理解地震周期和相关灾害是很重要的。此外，本科生将作为顶峰课程的一部分，参与这个项目的现场和分析部分，获得宝贵的机会，接触到数值建模人员(理论家)和现场地质学家(经验学家)之间的科学合作的好处。为这个项目选择的现场地点是加拿大魁北克的Morin切变区。其西部完全变形斜长岩。斜长石在这块岩石中所占的比例很大，这意味着它可以被有效地视为单一相，并利用实验室对斜长石力学行为的大量限制。该项目基于野外和实验室约束与数值地球动力学模型之间的紧密结合。具体任务将是：1)记录剪切带的变形条件、结构和现场演化；2)对脆性断层附近下地壳的应变梯度进行数值模拟和预测，没有任何削弱过程；3)从现场报告可能影响流变学和削弱岩石的微观构造或化学变化的证据；以及4)对任何可疑的削弱过程对剪切带几何和结构的影响进行数值评估。在这个项目的结论中，研究人员将确定所观察到的剪切带是由走滑系统中较高的脆性断层施加的变形所致，还是需要减弱机制来产生所观察到的模式。该项目还将展示在构造地质学中整合基于现场的研究和数值模拟研究的力量。此外，该项目将吸引本科生参加研究实习和非野外夏令营的顶峰体验。这些学生将直接接触到我们的观察和理论相结合的方法，并将更好地欣赏目前地质科学研究的专业知识和兴趣。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Earth’s crust deforms by different processes at different depths. The lower part of the crust is difficult to access in the field and is therefore less understood than the upper crust. Although earthquakes typically occur in the upper crust, the lower crust affects earthquake activity by transferring stress to shallower faults. Using a combination of field studies, laboratory analyses, and numerical models, this project will evaluate which processes allowed deformation to occur in narrow zones in the lower crust. This project will use an exposure of lower crustal deformation that at the surface in Québec, Canada, allowing us to directly study the rocks and deformational processes. In particular, the researchers will determine if interaction with shallower earthquake-causing faults in the upper crust is sufficient to explain the characteristics of this region, or if additional rock weakening processes play a fundamental role. This relationship between upper and lower crustal deformation is important to understand the earthquake cycle and related hazards. In addition, undergraduate students will participate in both the field and analytical portions of this project as part of a capstone class, gaining valuable exposure to the benefits of scientific collaboration between numerical modelers (theoreticians) and field geologists (empiricists).The field site selected for this project is the Morin Shear Zone in Québec, Canada. Its western portion exclusively deforms anorthositic rock. The large proportion of plagioclase in this rock means that it can be treated it as effectively a single phase and take advantage of the abundance of laboratory constraints on the mechanical behavior of plagioclase. This project is based on tight integration between constraints from the field and laboratory and numerical geodynamic modeling. Specific tasks will be to: 1) document shear zone deformation conditions, structure, and evolution from the field; 2) numerically model and predict strain gradients in the lower crust near a brittle fault, absent of any weakening processes; 3) report from the field evidence of microstructural or chemical changes that may affect rheology and weaken rocks; and 4) numerically evaluate the impact of any suspected weakening processes on shear zone geometry and structure. At the conclusion of this project, the researchers will have determined whether the observed shear zone results from deformation imposed by a brittle fault higher in the strike-slip system, or whether weakening mechanisms are necessary to cause the observed pattern. The project will also demonstrate the power of integrating field-based studies and numerical modeling studies in structural geology. Furthermore, this project will engage undergraduate students in research internships and in a non-field camp capstone experience. These students will have direct exposure to our combined observational and theoretical approaches, and will gain a better appreciation for the range of expertise and interests of current research in the geological sciences.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.