Experimental Constraints on Crustal Rheology

下地壳流变学控制着一系列广泛的过程，这些过程对于理解板块边界剪切带的发展和演化、地震灾害、壳幔地球化学演化、地幔流动与地壳动力学的耦合以及造山带的长期支持作用具有重要意义。虽然描述下地壳岩石流动行为的现有定律可以解释许多地质观测，但将这些定律外推到适合下大陆地壳的条件表明，可以用新的实验数据改进对岩石学和地质学数据的解释。该项目的目标是提供关于岩石在适合于下大陆地壳的压力下流变学的新实验数据。该项目将涉及三条调查线，涉及在900至1100摄氏度的温度和500 MPa至1.5 GPa的围压下在Griggs和Paterspm变形装置中进行的一系列实验。这些实验将解决以下问题：（1）水对下地壳岩石流变学/粘度的作用。初步工作表明，随着水含量的增加，二甘醇的粘度发生了显著变化。这些结果将扩展到更高温度/更低应力，以提高外推到自然条件的分辨率;（2）动态重结晶和岩石组构（即，晶格择优取向）的发展。初步实验工作的结果挑战了以前基于自然变形岩石分析的解释。然而，从表面上看，对天然岩石的解释与其他地质数据保持一致。解决这个问题需要更好地理解变形过程中的晶粒尺寸演化，更好地理解斜长石的晶格择优取向发展。(3)闪石的流变学尽管角闪石在地壳流变学中具有重要意义，而且普遍存在于中下地壳剪切带中，但关于角闪石流变学的实验却很少。数据的缺乏部分反映了角闪石由于其有限的热稳定性而难以在实验室中变形。受天然岩石中微结构的启发，研究人员将使用非常细粒度的聚集体来探索角闪石中低应力变形过程的作用，这是一种新的方法。了解下地壳的流变学性质对于一系列地球动力学问题是重要的。了解地壳流变学的最重要原因可能是为了准确评估孕震断层随时间变化的载荷所产生的地震危险--这可以通过大地测量研究来量化。在这项研究工作中使用的技术涉及电子显微镜和机械测试设备的最先进的应用，弥合材料科学和地质科学之间的差距。该项目的另一个组成部分将是创建一个可搜索的档案结果从以前的变形实验在布朗大学岩石力学实验室。该档案将包含超过40年研究的2000多个实验的信息。访问这样一个数据库将促进新的想法，并鼓励直接实验岩石变形社区以外的科学家探索流变数据和相关的微观结构与他们自己的研究。

The rheology of the lower continental crust controls a wide range of processes that are important for understanding the development and evolution of plate boundary shear zones, seismic hazards, the geochemical evolution of the crust and mantle, the coupling of mantle flow and crustal dynamics and the long-term support of mountain belts. While existing laws that describe the flow behavior of lower crustal rocks can explain many geologic observations, the extrapolation of these laws to conditions appropriate for lower continental crust indicates that the interpretation of geophysically- and geologically-derived data can be improved with new experimental data. The goal of this project is to provide new experimental data on the rheology of rocks at pressures appropriate for the lower continental crust. The project will involve three lines of investigation involving a set of experiments conducted in a Griggs and Paterspm deformation apparatuses at temperatures from 900 to 1100 degrees C and strain at confining pressures from 500 MPa to 1.5 GPa. These experiments will address the following: (1) The role of water on rheology/viscosity of lower crustal rocks. Initial work demonstrates dramatic changes in viscosity of diabase with increasing water content. These results will be extended to higher temperature/lower stress to increase the resolution of extrapolation to natural conditions; (2) Dynamic recrystallization and rock fabric (i.e., lattice preferred orientations) development in plagioclase. The results of initial experimental work challenge previous interpretations based on analyses of naturally deformed rocks. However, at face value, interpretation of the natural rocks remains consistent with other geological data. Resolution of this issue requires better understanding of grain size evolution during deformation, and better understanding of lattice preferred orientation development in plagioclase. (3) Rheology of amphibole. There are very few experiments on the rheology of amphibole, despite its importance for crustal rheology and ubiquitous presence in mid- to lower-crustal shear zones. The lack of data partly reflects difficulty in deforming amphibole in the lab owing to its limited thermal stability. Motivated by microstructures in natural rocks, the researchers will use very fine-grained aggregates to explore the role of low stress deformation processes in amphibole, which is a new approach. Understanding the rheological properties of the lower crust is important for a broad range of geodynamic problems. Probably the most important reason to understand crustal rheology is for the accurate assessment of earthquake hazards produced by time-dependent loading of seismogenic faults - as may be quantified by geodetic studies. The techniques used in this research effort involve state of the art application of electron microscopy and mechanical testing equipment which bridge the gap between materials science and the geological sciences. An additional component of the project will be the creation of a searchable archive of results from previous deformation experiments in the Brown University Rock Mechanics laboratory. The archive will contain information from more 2000 experiments covering more than 40 years of research. Access to such a database will facilitate new ideas and encourage scientists outside of the immediate experimental rock deformation community to explore rheological data and attendant microstructures pertinent to their own research.