Two-Phase Damage Theory and the Generation of Plate Tectonics

两相损伤理论与板块构造的生成

• 批准号: 0537599
• 负责人: David Bercovici
• 金额: $ 33.5万
• 依托单位: Yale University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-03-15 至 2011-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0537599&HistoricalAwards=false
• 关键词: Two; Phase; Damage; Theory; Generation

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).

剪切局部化是固体材料中的变形高度集中成窄带从而削弱材料的过程。 剪切局部化在物理学、材料科学和地球科学的许多领域中都很明显。在最大尺度上，它在板块构造如何由地球岩石地幔的热对流产生方面发挥着重要作用。在过去的几十年里，对岩石如何变形（流动、破裂、弯曲等）的研究表明，岩石圈（地表附近最冷、最坚固的部分）的长期变形可能是由复杂的行为控制的例如同时破碎和流体状流动；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，因此在构造板块之间边界的演化和结构中发挥着至关重要的作用，世界上大多数火山活动和地震活动都集中在构造板块之间。 因此，从岩石圈-地幔系统中的微裂纹产生和晶粒尺寸减小来发展构造板块边界的完整理论对于理解板块构造是如何由地幔对流产生的至关重要。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）最简单的形式是两相材料（岩石相和代表空隙填充或粒间物质的流体相） ; (2) 造成损坏的能量是作为表面能存储在裂纹壁和/或晶界上的变形功。 该理论已被用于预测剪切局部化、岩石中的破坏包络线以及从简单的流体动力学模型中生成板状运动。 这些结果强调了地幔-岩石圈动力学模型中裂纹或空洞生成损伤与晶粒尺寸减小损伤的重要性以及两者之间的竞争。 正在进行的项目将以下新的重要物理学纳入理论：（1）晶粒-晶界； (2) 相之间的质量交换和化学反应（例如愈合、熔化等）； (3)粗化和损坏导致的晶粒尺寸和晶粒尺寸分布的演变。 构建了与岩石圈压缩、伸展、剪切、重力塌陷和对流驱动流相关的应用程序，以测试添加到理论中的各种新物理效应。 这项工作进一步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，因此对地质流体力学（岩浆动力学、冰川学和水文系统）、岩石力学（小规模损伤区、局部化和破坏）以及普通材料科学的许多问题做出了贡献和工程（例如，弹力损伤、冶金和复杂流体，如胶体和悬浮液）。