Experimental Constraints on the Rheology of the Lower Continental Crust

下陆壳流变学的实验约束

• 批准号: 0810188
• 负责人: James Hirth
• 金额: $ 26万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-07-01 至 2012-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0810188&HistoricalAwards=false
• 关键词: Experimental; Constraints; Rheology; Lower; Continental

The goal of this proposal is to provide new experimental data on the rheology of mafic crustal rocks at temperatures and pressures appropriate for the lower continental crust. Rheology is the study of deformation and flow of matter under an applied stress. Understanding the rheological properties of the lower crust is important for a broad range of geologic problems. In terms of societal relevance, the most important reason to understand crustal rheology is for the accurate assessment of earthquake hazards produced by time-dependent loading of seismogenic faults. The rheology of the lower continental crust also controls the geochemical evolution of the crust and mantle (the chemical composition of the continental crust remains a controversial subject; one hypothesis that reconciles differences in current models supposes that melt that moves upwards from the mantle to the crust beneath volcanoes begins to crystallize at depths of ~30 km. As these crystals cool they become denser than the material below and thus can sink back into the mantle, but only if they are weak enough to flow at relatively rapid rates), the coupling of mantle flow to crustal dynamics (for example, how are movements at the Earth?s surface related to the long term convective motion in the interior) and the long-term support of mountain belts. Existing flow laws for mafic rocks do explain many geologic observations. However, extrapolation to conditions appropriate for the base of continental crust indicates that the interpretation of rheologic data derived using geophysical techniques could be improved with new experimental data.We propose to: (1) Conduct experiments on dry, coarse-grained gabbroic and plagioclase-rich rocks to provide creep data in the dislocation creep regime at conditions where we can minimize (a) the potential effects of microcracking and/or cavitation and (b) problems with resolving the relative contributions of diffusion creep and dislocation creep. (2) Quantify how water influences the rheological properties of plagioclase-rich rocks and evaluate how much water is needed to produce significant differences between dry and wet rheologies. (3) Determine if the phenomenal cavitation microstructures produced in lower pressure torsion experiments are inhibited at higher pressure. We will obtain rheological data at conditions beyond the conventional range used in gas medium machines ? and/or at temperature/strain rate conditions where brittle processes initiate at lower pressure. The experimental program will provide results that bridge the gap between different deformation apparatus, improving confidence in the application of laboratory mechanical data.

这项建议的目的是提供关于镁铁质地壳岩石在适合于下大陆地壳的温度和压力下的流变学的新的实验数据。流变学是研究物质在外加应力下的变形和流动的学科。了解下地壳的流变特性对一系列地质问题都很重要。就社会相关性而言，了解地壳流变学的最重要原因是为了准确评估孕震断层随时间变化的加载所产生的地震危险。 下大陆地壳的流变学也控制着地壳和地幔的地球化学演化（大陆地壳的化学成分仍然是一个有争议的主题;一个调和当前模型差异的假设认为，从地幔向上移动到火山下的地壳的熔体开始在约30公里的深度结晶。随着这些晶体冷却，它们变得比下面的物质更致密，因此可以沉回地幔，但前提是它们足够弱，可以以相对较快的速度流动），地幔流动与地壳动力学的耦合（例如，地球的运动如何？地表与内部长期对流运动有关）和山地带的长期支持。现有的镁铁质岩石流动规律确实解释了许多地质观测结果。然而，外推到适合于大陆地壳底部的条件表明，可以用新的实验数据改进对使用地球物理技术获得的流变数据的解释。（1）进行干燥、干燥、干燥。粗粒辉长岩和富含斜长石的岩石，以提供位错蠕变状态下的蠕变数据，在这些条件下，我们可以最大限度地减少（a）微裂纹的潜在影响和/或或空穴和（B）解决扩散蠕变和位错蠕变的相对贡献的问题。(2)量化水如何影响富含斜长石的岩石的流变特性，并评估需要多少水才能在干和湿流变学之间产生显着差异。(3)确定在较低压力扭转实验中产生的显著空化微结构是否在较高压力下受到抑制。我们将获得流变数据的条件超出了传统的范围内使用的气体介质机器？和/或在其中脆性过程在较低压力下开始的温度/应变速率条件下。该实验程序将提供弥合不同变形仪器之间的差距的结果，提高实验室力学数据应用的置信度。