Experimental Constraints on the Rheology of the Lower Continental Crust

这一建议的目的是提供新的实验数据在温度和压力下的基性地壳岩石流变适合于下大陆地壳。流变学是研究物质在外加应力作用下的变形和流动的学科。了解下地壳的流变特性对于解决许多地质问题都是很重要的。就社会相关性而言，了解地壳流变学最重要的原因是为了准确评估由发震断层的时变载荷产生的地震危害。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；一种假设调和了当前模型的差异，假设火山下面从地幔向上移动到地壳的熔体在约30公里深处开始结晶。随着这些晶体冷却，它们变得比下面的物质密度更大，因此可以沉入地幔，但前提是它们足够弱，可以以相对快的速度流动)，地幔流动与地壳动力学的耦合(例如，地球的运动是如何的？S面与内部的长期对流运动有关)和山带的长期支撑。现有的基性岩石流动规律确实解释了许多地质观测。然而，对适合大陆地壳基底条件的外推表明，利用地球物理技术得到的流变学数据的解释可以通过新的实验数据得到改进。我们建议：(1)对干燥、粗粒辉长岩和斜长岩进行实验，在可以最小化(a)微裂纹和/或空化的潜在影响以及(b)解决扩散蠕变和位错蠕变相对贡献的问题的条件下，提供位错蠕变体系中的蠕变数据。(2)量化水如何影响富斜长石岩石的流变学性质，并评估需要多少水才能产生干流变学和湿流变学之间的显著差异。(3)确定低压扭转实验中产生的现象性空化微观结构在高压下是否被抑制。我们将在超出气体介质机器常规范围的条件下获得流变数据。和/或在温度/应变速率条件下，脆性过程在较低的压力下开始。实验程序将提供的结果，弥合不同的变形设备之间的差距，提高实验室力学数据应用的信心。

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.