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.

该项目包括对晶格缺陷的作用进行实验和理论研究，晶格缺陷在纳米到微米尺度上具有空间特征，对代表上地幔岩石的矿物组合的塑性（永久变形）和滞弹性（与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原理）响应进行研究 地球的。 具体来说，我们将研究 (i) 异相边界（分隔不同矿物的晶体边界）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，纳米到微米尺度的缺陷（以及它们的空间分布，也在微米尺度）影响了公里甚至更大尺度的机械响应。 在时间上，我们必须选择适当的应力和温度热力学势以及适当的岩石微观结构，以便通过实验室实验（需要数小时才能完成）来模拟地球在地质时间内活跃的变形物理过程。 从技术上讲，实验工作强调（a）晶粒和异相边界滑动在相空间分离（变质分层）和结构（即矿物 CPO 的晶体学择优取向）发展中的作用； (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) 多晶聚集体中的瞬态蠕变/衰减响应与其应力松弛响应的相关性。 理论方面强调（a）非平衡热力学在应变影响的相分离问题中的应用，以及（b）塑性“状态方程”在多晶聚集体衰减响应中的应用。这项工作在地球物理学中有多种应用。 通过地震数据的解释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。地震学界有兴趣了解以下因素的影响：(i) 织物、(ii) 化学势（特别是水和氧气）和 (iii) 应变影响的层状结构对衰减的影响。 活动构造学界对与衰减相关的瞬态蠕变微观物理非常感兴趣。 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，迄今为止，这些现象在衰减/瞬态蠕变的实验研究中很少受到关注。 两者都将是这项工作的重点。 此外，科学本身还解决了（i）通过大塑性应变进行“原子自组装”和（ii）能量耗散的长度尺度的问题；与具有独特物理（因而经济）特性的分层材料（例如，将高刚度与高阻尼相结合的材料、具有独特电学或光学响应的​​多层或渗透结构等的材料）相关的理论及其发展可以预见为正在进行的研究的“副产品”。