Fabric Evolution and the Development of Ductile Shear Zones

众所周知，在剪切带中，岩石圈的变形在一定程度上是局部化的。这些剪切带的起源和整体力学行为仍然知之甚少。为了说明它们在构造中的作用，重要的是要了解它们的起源，无论是早期构造事件的疤痕还是自发产生的软弱带。一个关键是要限制他们的流变学，为此，它是至关重要的，以了解变形过程中活动的韧性剪切带，以及他们的架构。该项目旨在从理论和力学角度更好地限制地震活动断层下岩石圈的结构。具体而言，该项目将探讨韧性剪切带的形成及其与地震周期的联系。使用专门为此项目开发的软件，将模拟走滑断层下韧性剪切带的发展，特别揭示剪切带结构、宽度和强度可能如何随深度变化。该项目将解决当前计算机模型中的一个重大弱点，即它们没有充分纳入变形局部化过程。该项目有可能通过以下方式促进预期的社会成果：1）通过培养博士后研究员，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;和3）通过开发可供他人重复使用的新的开放获取软件，发展研究基础设施。该项目的目标是开发岩石圈的数值模型在走滑环境中变形该模型将包括地壳中的组构演化和地幔中的粒度演化，以确定韧性流动可能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）使用有限元库deal.II的二维抗剪切模型，将跟踪脆性断层下剪切带的发展; 3）脆性断层上地震的幕式加载的相同模型。该项目将评估通过岩石圈定位的三种不同方案。首先，自发本地化是唯一的球员在整个脆性以及韧性水平的岩石圈，以确定如何粒度演化和发展的层状结构的韧性上地幔和中，下地壳相互作用的应变弱化脆性制度，形成岩石圈规模的剪切带。其次，这项研究将强加一个预先存在的脆性断层，并确定如何韧性剪切可能在它下面本地化，一个场景，包括强加和自发本地化。最后，将考虑地震周期的影响，它周期性地对不断发展的剪切带施加增强的应力。这些模型将提供有关韧性剪切带的结构、强度和宽度的基本知识，这些韧性剪切带可能在活跃变形区的深度处出现。

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.