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

地壳在不同深度的变形过程不同。地壳的下部在野外很难接近，因此比上部地壳了解得少。虽然地震通常发生在上地壳，但下地壳通过将应力传递给较浅的断层来影响地震活动。通过实地研究、实验室分析和数值模型的结合，该项目将评估哪些过程导致了下地壳狭窄地带的变形。这个项目将使用在加拿大qusamubec地表下地壳变形的暴露，使我们能够直接研究岩石和变形过程。特别是，研究人员将确定是否与上地壳中引起地震的浅层断层的相互作用足以解释该地区的特征，或者是否额外的岩石弱化过程起了基本作用。上下地壳变形之间的这种关系对于理解地震周期和相关的灾害是很重要的。此外，作为顶点课程的一部分，本科生将参与该项目的实地和分析部分，从而获得数值建模者（理论家）和实地地质学家（经验主义者）之间科学合作的宝贵机会。本项目选择的现场是加拿大qusamubec的Morin剪切带。它的西部部分只变形斜长岩。斜长石在该岩石中所占的比例很大，这意味着它可以被有效地视为单相，并利用斜长石力学行为的丰富实验室约束。该项目基于现场和实验室约束与数值地球动力学建模的紧密结合。具体任务将是：1)记录剪切带的变形条件、结构和演变；2)在没有任何弱化过程的情况下，对脆性断裂附近下地壳应变梯度进行数值模拟和预测；3)可能影响流变和削弱岩石的微观结构或化学变化的现场证据报告；4)数值评价任何可能的弱化过程对剪切带几何和结构的影响。在本项目结束时，该项目将确定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造成的，还是需要削弱机制来导致观察到的模式。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进行研究实习和非实地营顶点体验。这些学生将直接接触到我们结合观察和理论的方法，并将更好地了解当前地质科学研究的专业知识和兴趣范围。该奖项反映了美国国家科学基金会的法定使命，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。

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 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 project 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.