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

异相边界和亚晶界在橄榄岩塑性和滞弹性（衰减/瞬态蠕变）响应中的作用

• 批准号: 1014476
• 负责人: Reid Cooper
• 金额: $ 54.5万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1014476&HistoricalAwards=false
• 关键词: Roles; Heterophase; Boundaries; Subgrain; Plastic

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.

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地球。 具体而言，我们将检查（i）（i）异物相边界（分隔不同矿物质的晶体边界）和（ii）机械动力学上的亚晶边界（组成晶体中的晶体部分结构体）扮演的角色。 这项工作强调了空间和时间缩放。 从空间上讲，它是纳米到微电仪的尺度缺陷（及其空间分布，也以微米尺度为单位），在较大的尺度和更大的尺度上影响机械响应。 时间上，必须选择应力和温度的适当热力学潜力和适当的岩石微观结构，以模仿地质时间在地球上活跃的变形物理学，而在实验室实验中活跃的人则在数小时内完成。 从技术上讲，实验工作强调了（a）晶粒和异物相结合的滑动在空间分离相（变质分层）和织物（即矿物质-CPO的晶体偏爱的方向）中的作用； （b）与这两种现象相关的瞬态蠕变和相关的衰减动力学； （c）相位分离作为流动应力的函数以及这种缩放对衰减的影响； （d）多晶骨料中瞬时蠕变/衰减反应与应力松弛中的响应的相关性。 理论方面强调（a）将非平衡热力学应用于应变相分离的问题，以及（b）将可塑性“状态方程”应用于多晶骨料的衰减响应。这项工作在地球物理中有多个应用。 通过解释地震数据来辨别地球地幔的结构取决于理解组成矿物和岩石的无弹性反应。地震界有兴趣了解，例如（i）（i）（ii）化学势（特别是水和氧）和（iii）应变层状结构对衰减的影响。 活跃的构造界对与衰减有关的瞬态蠕变的微物理学非常感兴趣。 这些现象都不仅受晶界过程的影响/影响，而且还受到脱位运动和相关脱位结构的影响，到目前为止，在衰减/瞬态蠕变的实验研究中，几乎没有关注。 两者都将是这项工作的重点。 此外，科学本身通过大型塑性应变和（ii）能量消散的长度尺度来解决（i）“原子自组装”的问题；与层次材料有关的理论及其发展具有独特的物理（以及经济）特性（例如，将高刚度与高阻尼，多层或渗透性结构与独特的电或光学响应等相结合的材料，可以预期为“副产物”的研究。