Low-Frequency Attenuation in Polycrystalline Silicates and Silicate Partial Melts

多晶硅酸盐和硅酸盐部分熔体的低频衰减

• 批准号: 0106620
• 负责人: Reid Cooper
• 金额: $ 8.7万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-01 至 2003-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0106620&HistoricalAwards=false
• 关键词: Low; Frequency; Attenuation; Polycrystalline; Silicates

Cooper 0106620 The experimental measurement of the low-frequency attenuation behavior of polycrystalline olivine, of olivine-orthopyroxene and of olivine-based partial melts is the practical emphasis of this research. Of theoretical focus is a new hypothesis concerning the physical mechanism(s) and significance of the "high-temperature background" mechanical absorption, specifically, that this absorption relates to the diffusion-effected relaxations of grain and solid-state phase boundaries and particularly of (deformation-induced) subgrain boundaries. The physical implication, then, is that a small-amplitude, oscillatory variation in stress, one that is added to a nominally constant differential stress that is effecting dislocation creep in a material, is "sampling" the deformation-induced microstructure, specifically the network of subgrains. If this hypothesis is correct--and discerning this correctness is the long-range goal of the experimental work--one can envision an effective way to do attenuation-based "geophysical prospecting" of active tectonic regions, e.g., for levels of differential stress and, perhaps, strain, with a calibration based on laboratory experiments. Experiments in this (one-year) funding period will emphasize dynamic ("sub-resonant" oscillatory loading) and quasi-static (constant loading, i.e., creep), high-resolution torsional mechanical responses of carefully engineered aggregates of (ferromagnesian) olivine and of two-phase solid olivine-orthopyroxene. These will be studied as functions of (i) temperature (1150-1350 degC), (ii) frequency (10^[-4]-1 Hz) and (iii) grain size (5-20 micrometers; fine enough that [a] thermal-expansion-anisotropy effected grain/phase boundary cracking cannot occur and [b] [for the levels of differential stress employed] lattice dislocations are not nucleated in the course of mechanical testing). In addition, benchmarking deformation experiments, comparing the high-resolution ambient-pressure measurements with the mechanical response of the same material under a confining pressure of ~300 MPa will be performed.

Cooper 0106620 多晶橄榄石、橄榄石-斜方辉石和橄榄石基部分熔体的低频衰减行为的实验测量是本研究的实际重点。 理论焦点是关于“高温背景”机械吸收的物理机制和意义的新假设，具体来说，这种吸收与晶粒和固态相边界，特别是（变形引起的）亚晶界的扩散效应弛豫有关。 那么，物理含义是，应力的小幅度振荡变化（添加到影响材料中位错蠕变的名义上恒定的差异应力中）正在“采样”变形引起的微观结构，特别是亚晶网络。 如果这个假设是正确的——并且辨别这种正确性是实验工作的长期目标——人们可以设想一种有效的方法，对活动构造区域进行基于衰减的“地球物理勘探”，例如，通过基于实验室实验的校准来确定不同应力水平，也许还有应变水平。 这一（一年）资助期间的实验将强调动态（“亚共振”振荡载荷）和准静态（恒定载荷，即蠕变）、精心设计的（铁镁）橄榄石和两相固体橄榄石-斜方辉石聚集体的高分辨率扭转机械响应。这些将被研究为 (i) 温度 (1150-1350 摄氏度)、(ii) 频率 (10^[-4]-1 Hz) 和 (iii) 晶粒尺寸 (5-20 微米) 的函数；足够精细，[a] 热膨胀各向异性影响的晶粒/相边界裂纹不会发生，并且 [b] [对于所采用的差异应力水平] 晶格位错在机械加工过程中不会成核 测试）。 此外，还将进行基准变形实验，将高分辨率环境压力测量结果与相同材料在约 300 MPa 围压下的机械响应进行比较。