Two-Phase Damage Theory and the Generation of Plate Tectonics

剪切局部化是固体材料中的变形高度集中到削弱材料的窄带中的过程。 剪切局部化在物理学、材料科学和地球科学的许多领域都很明显;在最大的尺度上，它在板块构造如何从地球岩石地幔的热对流中产生中起着重要作用。在过去的几十年里，对岩石如何变形（流动、破裂、弯曲等）的研究，已经表明，岩石圈的长期变形（靠近地表的地幔最冷最坚固的部分）可能受到复杂行为的控制，例如同时断裂和类似流体的流动;以及岩石内部矿物颗粒尺寸的减小。 已知这种机制会导致集中或局部变形，从而在构造板块之间边界的演变和结构中发挥关键作用，而世界上大多数火山活动和地震活动都集中在这些板块上。 因此，发展一个完整的理论，从岩石圈-地幔系统中的微裂纹生成和粒度减小的构造板块边界生成是至关重要的了解板块构造如何产生地幔对流。该项目继续发展一种称为两相损伤理论的新理论。该理论指出：（1）受损材料（具有空隙/微裂纹、缺陷、晶界）在其最简单的形式中是两相材料（岩石相和代表空隙填充或粒间物质的流体相）;以及（2）进入损伤的能量是变形功，其作为表面能存储在裂纹壁和/或晶界上。 该理论已被用来预测剪切局部化，在岩石中的失败信封，并从简单的流体动力学模型的板状运动的产生。 这些结果强调的重要性，和竞争之间，裂纹或空洞产生的损害和粒度减少损害的地幔岩石圈动力学模型。 正在进行的项目将以下新的重要物理学纳入理论：（1）晶粒间界;（2）相之间的质量交换和化学反应（例如，愈合，熔化等）;（3）在晶粒和粒度分布的粗化和损伤的演变。 岩石圈的压缩，拉伸，剪切，引力坍缩，对流驱动流相关的应用程序被构建来测试各种新的物理效应，被添加到理论。 这一工作加深了我们对地幔动力学、岩石圈变形和板块构造起源的基本过程的理解。此外，由于该项目涉及基础理论，它有助于解决地质流体力学（岩浆动力学，冰川学和水文系统），岩石力学（小尺度损伤区，局部化和破坏）以及一般材料科学和工程（例如，弹性动力学损伤、冶金和复杂流体（如胶体和悬浮液）。

Shear localization is the process by which deformation in a solid material becomes highly focused into narrow bands that weaken the material. Shear localization is apparent in many fields of physics, materials science and geoscience; at the largest scale, it plays an important role in how plate tectonics arises from thermal convection in the Earth's rocky mantle. In the last few decades, studies of how rocks deform (flow, break, bend, etc.) have shown that the long-term deformation of the lithosphere (the coldest strongest part of the mantle near the surface) is likely controlled by complex behavior such as simultaneous breaking and fluid-like flow; and reduction in the size of mineral grains inside of rocks. Such mechanisms are known to lead to focused or localized deformation and thus play a crucial role in the evolution and structure of boundaries between tectonic plates upon which most of the worlds volcanism and seismicity are focused. Thus, the development of a complete theory of tectonic plate boundary generation from microcrack generation and grainsize reduction in the lithosphere-mantle system is paramount for understanding how plate tectonics arises out of mantle convection. This project continues development of one such new theory called two-phase damage theory. This theory states that (1) a damaged material (with voids/microcracks, defects, grain boundaries) is, in its simplest form, a two-phase material (a rock phase, and a fluid phase representing void-filling or intergranular matter); and (2) the energy going into damage is deformational work that is stored as surface energy on the crack wall and/or grain boundary. The theory has been used to predict shear localization, failure envelopes in rocks, and generation of plate-like motion from simple fluid-dynamical models. These results stress the importance of, and competition between, crack- or void-generating damage and grainsize reducing damage in models of mantle-lithosphere dynamics. The ongoing project incorporates into the theory new important physics of (1) grain-grain boundaries; (2) mass exchange and chemical reactions between phases (e.g., for healing, melting, etc); and (3) evolution in grainsizes and grainsize distributions by coarsening and damage. Applications relevant to lithospheric compression, extension, shear, gravitational collapse, and convectively driven flow are constructed to test the various new physical effects that are added to the theory. This work furthers our understanding of the fundamental processes of mantle dynamics, lithospheric deformation and the origin of plate tectonics. Moreover, since the project involves a fundamental theory, it contributes to many problems of geological fluid mechanics (magma dynamics, glaciology, and hydrological systems), rock mechanics (small-scale damage zones, localization and failure), as well as general material science and engineering (e.g., elastodynamic damage, metallurgy, and complex fluids such as colloids and suspensions).