The Roles of Heterophase Boundaries and Subgrain Boundaries in the Plastic and Anelastic (Attneuation/Transient Creep) Responses of Peridotite

该项目包括一个实验和理论研究晶体晶格缺陷的作用，其空间特征在纳米到微米尺度，在塑性（永久变形）和非弹性（时间相关的可恢复或瞬态变形，这是地震波衰减的来源和机械松弛背后的物理）的矿物组合代表地球上地幔岩石的响应。具体来说，我们将研究(i)异相边界（分离不同矿物的晶体边界）和（ii）亚晶界（组成晶体内的晶体部分边界）在机械动力学上所起的作用。这项工作强调空间和时间尺度。在空间上，是纳米到微米尺度的缺陷（及其空间分布，也在微米尺度上）影响千米及更大尺度的机械响应。在时间上，人们必须选择适当的应力和温度的热力学势和适当的岩石微观结构，以便模拟地球在地质时期活跃的变形物理与实验室实验中活跃的物理变形，这些实验需要几个小时才能完成。从技术上讲，实验工作强调(a)晶粒和异相边界滑动在相的空间分离（变质分层）和织构（即矿物的晶体学优选取向- cpo）的发展中的作用；(b)瞬态蠕变和与这两种现象相关的衰减动力学；(c)相分离的空间尺度作为流动应力的函数，以及这种尺度对衰减的影响；(d)多晶聚集体的瞬态蠕变/衰减响应与应力松弛响应的相关性。理论方面强调(a)将非平衡热力学应用于应变影响的相分离问题，以及(b)将塑性“状态方程”应用于多晶聚集体的衰减响应。这项工作在地球物理学中有多种应用。通过对地震数据的解释来识别地幔的结构取决于对组成矿物和岩石的非弹性反应的理解。地震学界感兴趣的是了解(i)结构，（ii）化学势（特别是水和氧）和（iii）受应变影响的层状结构对衰减的影响。活动构造界对与衰减有关的瞬变蠕变的微物理现象非常感兴趣。这些现象不仅受到晶界过程的影响，还受到位错运动和相关位错结构的影响，迄今为止在衰减/瞬态蠕变的实验研究中很少受到重视。这两者都将是本工作的重点。此外，科学本身解决了(i)通过大塑性应变的“原子自组装”问题和（ii）能量耗散的长度尺度；与具有独特物理（以及经济）特性的分层材料相关的理论及其发展（例如，结合高刚度和高阻尼的材料，具有独特电学或光学响应的多层或渗透结构等）可以作为正在进行的研究的“副产品”进行预期。

This project comprises an experimental and theoretical study of the roles of crystal-lattice defects, which are characterized spatially at the nanometer-to-micrometer scale, on the plastic (permanent deformation) and anelastic (time-dependent recoverable, or transient, deformation, which is the source of the attenuation of seismic waves and the physics behind mechanical relaxation) responses of mineral assemblages representative of the upper-mantle rock of Earth. Specifically, we will examine the roles played by (i) heterophase boundaries (crystalline boundaries separating different minerals) and (ii) subgrain boundaries (crystalline partial-boundaries within component crystals) on the mechanical dynamics. The work emphasizes both spatial and temporal scaling. Spatially, it is the nanometer-to-micrometer scale defects (and their spatial distribution, also at the micrometer scale) that effect the mechanical response at the scale of kilometers and greater. Temporally, one must select appropriate thermodynamic potentials of stress & temperature and appropriate rock microstructure so as to mimic the physics of deformation active in the Earth over geological time with those active in laboratory experiments, which are completed over hours. Technically, the experimental work emphasizes (a) the role of grain- and heterophase-boundary sliding in the development both of spatial separation of phases (metamorphic layering) and of fabric (i.e., crystallographic-preferred orientation of minerals-CPO); (b) the transient creep and, related, attenuation dynamics associated with both of these phenomena; (c) the spatial scaling of phase separation as a function of flow stress and the impact of such scaling on attenuation; (d) the correlation of transient creep/attenuation responses in polycrystalline aggregates with their response(s) in stress relaxation. The theoretical aspect emphasizes (a) application of nonequilibrium thermodynamics to the problem of strain-effected phase separation and (b) application of a plasticity "equation-of-state" to the attenuation response of polycrystalline aggregates. The work has multiple applications in geophysics. Discerning the structure of Earth's mantle through interpretation of seismic data depends on understanding the anelastic response(s) of the constituent minerals and rock. The seismology community is interested in understanding the effects of, e.g., (i) fabric, (ii) chemical potentials (specifically of water and oxygen) and (iii) strain-effected layered structures on attenuation. The active tectonics community is deeply interested in the microphysics of transient creep, which is related to attenuation. These phenomena are all affected/effected not only by grain boundary processes, but also by dislocation motion and related dislocation structures, which have received, so far, little attention in experimental studies of attenuation/transient creep. Both will be the emphases of this work. Additionally, the science itself addresses issues of (i) 'atomic self-assembly' via large plastic strain and (ii) the length scales of energy dissipation; theories and their development relating to hierarchical materials with unique physical (and, thus, economical) properties (e.g., materials combining high stiffness with high damping, multilayer or percolative structures with distinctive electrical or optical response, etc.) can be anticipated as a 'by-product' of the research being pursued.