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

该项目包括晶体晶格缺陷的作用的实验和理论研究，其特征在于在纳米到微米尺度的空间，在塑料（永久变形）和滞弹性（时间依赖的可恢复的或瞬时的变形，这是地震波衰减和机械松弛背后的物理学的来源）代表上部-地球的地幔岩 具体而言，我们将研究（i）异相边界（分隔不同矿物的晶界）和（ii）亚晶界（组分晶体内的晶体部分边界）对机械动力学的作用。 这项工作强调空间和时间尺度。 在空间上，正是纳米到微米尺度的缺陷（以及它们的空间分布，也是在微米尺度上）影响了在千米和更大尺度上的机械响应。 在时间上，人们必须选择适当的应力温度热力学势和适当的岩石微观结构，以便模拟地质时期地球上活跃的变形物理学与实验室实验中活跃的变形物理学，这些实验需要数小时才能完成。 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）和组构（即，矿物的晶体学优选取向-CPO）;（B）与这两种现象相关的瞬态蠕变和相关的衰减动力学;（c）作为流动应力的函数的相分离的空间尺度以及这种尺度对衰减的影响;（d）多晶聚集体中的瞬态蠕变/衰减响应与它们在应力松弛中的响应的相关性。 理论方面强调（a）应用非平衡热力学的问题，应变影响相分离和（B）应用塑性“状态方程”的多晶聚集体的衰减响应。这项工作在天体物理学中有多种应用。 通过解释地震数据来辨别地幔的结构取决于对组成矿物和岩石的滞弹性响应的理解。地震学界对了解地震的影响很感兴趣，例如，(i)织物，（ii）化学势（特别是水和氧）和（iii）应变影响的衰减分层结构。 活动构造学界对与衰减有关的瞬态蠕变的微观物理学非常感兴趣。 这些现象不仅受到晶界过程的影响，而且还受到位错运动和相关位错结构的影响，但在衰减/瞬态蠕变的实验研究中，这些问题至今还很少受到重视。 两者都将是本工作的重点。 此外，科学本身解决了以下问题：（i）通过大塑性应变的“原子自组装”和（ii）能量耗散的长度尺度;与具有独特物理（因此，经济）特性的分层材料相关的理论及其发展（例如，高刚度与高阻尼相结合的材料，具有独特的电或光响应的多层或叠层结构等）可以被预期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.