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

地壳在不同的深度会因不同的过程而变形。地壳的下部在实地很难进入，因此人们对它的了解不如对上地壳的了解。 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。该项目将结合实地研究、实验室分析和数值模型，评估哪些过程使下地壳狭窄区域发生变形。 该项目将使用加拿大魁北克地表的下地壳变形暴露，使我们能够直接研究岩石和变形过程。特别是，研究人员将确定与上地壳中较浅的地震成因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。上下地壳形变之间的这种关系对于理解地震周期和相关灾害是很重要的。 此外，本科生将参与该项目的实地和分析部分，作为顶点课程的一部分，获得数值建模师（理论家）和实地地质学家（地质学家）之间科学合作的好处。该项目选择的实地地点是加拿大魁北克省的Morin剪切带。它的西部部分专门使斜长岩变形。这种岩石中斜长石的比例很大，这意味着它可以被有效地视为单相，并利用实验室对斜长石力学行为的大量限制。该项目是基于从现场和实验室的约束和数值地球动力学建模之间的紧密结合。具体任务是：1）从现场记录剪切带变形条件、结构和演化; 2）在没有任何弱化过程的情况下，对脆性断层附近的下地壳中的应变梯度进行数值模拟和预测; 3）从现场报告可能影响流变学和弱化岩石的微观结构或化学变化的证据;以及4）数值评估任何可疑的弱化过程对剪切区几何形状和结构的影响。在该项目结束时，研究人员将确定观察到的剪切带是否是由走滑系统中较高的脆性断层施加的变形造成的，或者是否需要弱化机制来引起观察到的模式。该项目还将展示在结构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，该项目将使本科生参与研究实习和非实地营地顶点体验。这些学生将直接接触到我们结合的观测和理论方法，并将获得更好的欣赏范围的专业知识和兴趣，目前的研究在地质科学。这个奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

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.