Fabric Evolution and the Development of Ductile Shear Zones

众所周知，在岩石圈的剪切带中，变形在每个深度都有一定程度的局部化。这些剪切带的起源和整体力学行为仍然知之甚少。为了解决它们在构造中的作用，重要的是要了解它们的起源，是早期构造事件的疤痕还是自发产生的弱带。关键是限制它们的流变性，为此，了解韧性剪切带中活跃的变形过程及其结构至关重要。该项目旨在从理论和力学的角度更好地约束地震活动断层下岩石圈的结构。具体而言，该项目将解决韧性剪切带的产生及其与地震旋回的联系。使用专门为该项目开发的软件，将模拟走滑断层下韧性剪切带的发展，特别是揭示剪切带的结构、宽度和强度如何随深度变化。该项目将解决当前计算机模型的一个重大弱点，即它们没有充分纳入变形定位过程。该项目有可能通过以下方式促进预期的社会成果：1)通过培训博士后，培养具有全球竞争力的STEM劳动力；2)通过国际合作加强伙伴关系；3)通过开发新的开放获取软件来开发研究基础设施，这些软件可以被其他人重用。本项目的目的是建立走滑环境下岩石圈变形的数值模型。该模型将包括地壳的结构演化和地幔的粒度演化，以确定韧性流动局部化并形成韧性剪切带的条件。本项目将开发三种模型：1)耦合局部剪切带演化模型的一维柱模型；2)建立二维抗剪模型，采用有限元库处理。II，在脆性断层下方将发育剪切带；(3)同一模型在脆性断裂上受地震的幕式荷载作用。该项目将评估三种不同的岩石圈定位方案。首先，在岩石圈的脆性和韧性水平上，自发局部化是唯一的参与者，它决定了韧性上地幔和中下地壳的粒度演化和层状结构的发展如何与脆性体系中的应变弱化相互作用，从而形成岩石圈尺度的剪切带。其次，该研究将施加一个预先存在的脆性断层，并确定韧性剪切如何在其下方局部化，这种情况包括强加的和自发的局部化。最后，将考虑地震周期的影响，周期性地对演化中的剪切带施加增强应力。这些模型将提供关于活跃变形区域深处可能出现的韧性剪切带的结构、强度和宽度的基本知识。

It is well known that deformation is localized to some extent at every depth in the lithosphere in shear zones. The origin and overall mechanical behavior of these shear zones remain poorly understood. To address their role in tectonics, it is important to understand their origin, whether a scar of earlier tectonics events or a spontaneously generated weak zone. A key is to constrain their rheology, and for this, it is critical to understand deformation processes active in ductile shear zones as well as their architecture. This project aims at better constraining, from a theoretical and mechanical point of view, the structure of the lithosphere beneath seismically active faults. Specifically, the project will address the generation of ductile shear zones and their link with the seismic cycle. Using a software developed specifically for this project, the development of a ductile shear zone beneath a strike-slip fault will be simulated, revealing in particular how the shear zone structure, width, and strength are likely to change with depth. This project would address one of the significant weaknesses in current computer models, which is that they do not adequately incorporate deformation localization processes. The project has potential to advance desired societal outcomes through: 1) development of a globally competitive STEM workforce through training of a post-doctoral fellow; 2) increased partnerships through international collaboration; and 3) development of research infrastructure through the development of new open access software that would be available for reuse by others.The objective of this project is to develop numerical models of the lithosphere deforming in a strike-slip environment. The model will include fabric evolution in the crust and grain size evolution in the mantle to determine the conditions under which ductile flow may localize and form a ductile shear zone. Three kinds of models will be developed in this project: 1) a 1-D column model that couples a local shear zone evolution model; 2) a 2-D antishear model, using the finite element library deal.II, that will follow development a shear zone below a brittle fault; and 3) the same model subjected to episodic loading by earthquakes on the brittle fault. The project will evaluate three different scenarios for localization through the lithosphere. First, spontaneous localization is the only player throughout the brittle as well as ductile levels of the lithosphere to determine how grain size evolution and the development of a layered structure in the ductile upper mantle and mid to lower crust interacts with strain-weakening in the brittle regime to form a lithospheric-scale shear zone. Second, the study will impose a preexisting brittle fault and determine how ductile shear may localize beneath it, a scenario that includes both imposed and spontaneous localization. Finally, the influence of the earthquake cycle, which periodically imposes episodes of enhanced stress on the evolving shear zones, will be considered. These models will provide basic knowledge on the structure, strength, and width of ductile shear zones that may be expected at depth in actively deforming regions.