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

该项目包括对晶格缺陷对代表地球上地幔岩石的矿物组合的塑性(永久变形)和滞弹性(随时间变化的可恢复或瞬时变形，这是地震波衰减和机械松弛背后的物理原因)反应的作用的实验和理论研究，这些缺陷的空间特征是纳米到微米级。具体地说，我们将研究(I)异相界(分隔不同矿物的晶界)和(Ii)亚晶界(成分晶体内的晶界)在力学动力学中所起的作用。这项工作同时强调了空间和时间尺度。在空间上，纳米级到微米级的缺陷(以及它们的空间分布，也是微米级的)在千米或更大的尺度上影响机械响应。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结构，以模拟地质时期地球上活跃的形变物理，以及那些在实验室实验中活跃的，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)晶界和异相界滑动在相空间分离(变质分层)和组构(即晶体择优取向-CPO)的发展中的作用；(B)与这两种现象相关的瞬时蠕变和相关的衰减动力学；(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)多晶聚集体的瞬时蠕变/衰减响应与它们在应力松弛中的响应(S)的关联。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”应用于多晶集合体的衰减响应。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辨别地幔的结构，有赖于了解组成矿物和岩石的滞弹性响应(S)。地震界感兴趣的是了解(I)组构、(Ii)化学势(特别是水和氧)和(Iii)应变影响的层状结构对衰减的影响。活动构造界对瞬变蠕变的微观物理非常感兴趣，它与衰减有关。这些现象不仅受晶界过程的影响，而且还受位错运动和相关的位错结构的影响，在衰减/瞬时蠕变的实验研究中尚未引起足够的重视。两者都将是这项工作的重点。此外，科学本身解决的问题是：(I)通过大的塑性应变进行的“原子自组装”；(Ii)能量耗散的长度尺度；与具有独特物理(因此，经济)属性的分级材料有关的理论及其发展(例如，结合高刚性和高阻尼性的材料、具有独特电学或光学响应的多层或渗流结构等)。可以预期作为正在进行的研究的“副产品”。

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.