Effects of Deformation-Induced Microstructure, Texture and the Spatial Distribution of Phases on the Steady-State Rheology and Attenuation Response(s) of Mantle Materials

变形引起的微观结构、织构和相空间分布对地幔物质稳态流变和衰减响应的影响

• 批准号: 0609869
• 负责人: Reid Cooper
• 金额: $ 37.2万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-11-01 至 2011-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0609869&HistoricalAwards=false
• 关键词: Effects; Deformation; Induced; Microstructure; Texture

Research Program Abstract: EAR-0609869Effects of Deformation-Induced Microstructure, Texture and the Spatial Distribution of Phases on the Steady-State Rheology and Attenuation Response(s) of Mantle MaterialsReid F. Cooper, Principal InvestigatorDepartment of Geological SciencesBrown UniversityThe geophysical understanding of the structure of Earth's upper mantle is predicated on the propagation velocity and absorption (attenuation) of seismic waves. Interpretation of seismological data depends on understanding the dynamic mechanical response of appropriate mineral assemblages as functions of a variety of thermodynamic and microstructural factors. The actual database for characterization of dynamic response at appropriate seismic and teleseismic frequencies is quite minimal; consequently, most seismological interpretations, e.g., of structure in Earth's upper mantle, are predicated on assumptions concerning the correlation of the attenuation response with the plastic (creep) response, where far more data are available. Recent experimental studies of attenuation in a variety of Earth and engineering materials indicate clearly, however, that the attenuation-creep correlation assumption is dubious at best, specifically because of inadequate consideration of spatial and temporal scaling effects in deformation. This project is an experimental and theoretical study of the effects of deformation-induced microstructure, texture and the spatial scaling of minerals on (i) the steady-state rheology and (ii) the attenuation response(s). Model upper-mantle materials--synthesized aggregates of dunite (polycrystalline olivine) and of harzburgite (polycrystalline mixture of olivine and orthopyroxene) as well as natural olivine single crystals--are studied. The experimental work emphasizes (a) characterization of spatial scaling of olivine-orthopyroxene phase separation as a function of the stress (or strain rate) and accumulated strain; (b) statistical characterization of deformation microstructure within the material via diffraction-based pole-figure analysis; (c) characterization of the stress-relaxation and "stress-dip" responses as a function of accumulated strain; and (d) direct measurement of attenuation response of deformed specimens. The theoretical work emphasizes application of Hart's [1970] plasticity equation-of-state model to the attenuation response of crystals and aggregates. This research addresses physical properties issues of direct interest to seismologists, particularly in the attempt to isolate effects, e.g., of "water," independent from that of temperature, on the attenuation response. But attenuation will be affected, too, by rock fabrics at a variety of scales (subgrain structure, lattice-preferred orientation and beyond), which have not yet been characterized on mineral assemblages at appropriate time-temperature conditions at all. Application (and proof-testing) of a stress-relaxation technique to the study of attenuation physics may allow knowledge of how to perform spatiotemporal extrapolation, as well as have the potential to isolate the effects of competing various thermodynamic factors on attenuation. The research pursues not only the reductionist physics of the microscopic mechanism(s) of attenuation in minerals, but moves beyond--to the nonequilibrium, dissipative thermodynamics of plasticity in rocks subjected to a relentless deviatoric stress. Thus, the science itself addresses issues of material "self-assembly" specifically through the use of large plastic strain; theories relating to hierarchical materials with unique physical (and, thus, economical) properties can be anticipated to be formulated through this research.

研究计划摘要：EAR-0609869变形诱导的微观结构、纹理和相的空间分布对地幔材料稳态流变学和衰减响应的影响Reid F.库珀，首席研究员布朗大学地质科学系地球物理学对地球上地幔结构的理解是基于地震波的传播速度和吸收（衰减）。 地震学数据的解释取决于对适当矿物组合的动态力学响应的理解，这些矿物组合是各种热力学和微观结构因素的函数。 在适当的地震和地震频率下，用于描述动态响应特性的实际数据库非常少;因此，大多数地震学解释，例如，地球上地幔的结构，是基于假设的衰减响应与塑性（蠕变）响应的相关性，其中有更多的数据。 然而，最近对各种地球和工程材料中的衰减的实验研究清楚地表明，衰减蠕变相关性假设充其量是可疑的，特别是因为没有充分考虑变形中的空间和时间尺度效应。 该项目是一个实验和理论研究的变形引起的微观结构，纹理和矿物的空间尺度的影响（i）的稳态流变学和（ii）的衰减响应（S）。 模型上地幔材料-纯橄榄岩（多晶橄榄石）和斜方辉石（橄榄石和斜方辉石的多晶混合物）以及天然橄榄石单晶的合成聚集体进行了研究。 实验工作强调（a）橄榄石-斜方辉石相分离的空间标度表征作为应力的函数（或应变率）和累积应变的关系;（B）通过基于衍射的极图分析对材料内的变形微观结构进行统计表征;（c）对作为累积应变的函数的应力松弛和“应力下降”响应进行表征;以及（d）变形试样的衰减响应的直接测量。 理论工作强调应用哈特的[1970]塑性状态方程模型的晶体和聚集体的衰减响应。 这项研究解决了地震学家直接感兴趣的物理性质问题，特别是在试图隔离影响时，例如，“水”对衰减响应的影响独立于温度的影响。 但是，衰减也会受到各种尺度（亚晶粒结构、晶格择优取向及更大尺度）的岩石组构的影响，这些尺度在适当的时间-温度条件下的矿物组合上还没有得到表征。 应用（和验证测试）的应力松弛技术的衰减物理学的研究，可以允许如何执行时空外推的知识，以及有可能隔离的各种热力学因素对衰减竞争的影响。 这项研究不仅追求矿物中衰减的微观机制的还原物理学，而且超越了-岩石中塑性的非平衡，耗散热力学受到无情的偏应力。 因此，科学本身解决了材料“自组装”的问题，特别是通过使用大的塑性应变;与具有独特物理（因此，经济）特性的分层材料相关的理论可以通过这项研究来制定。