Experimental Constraints on Crustal Rheology

地壳流变学的实验约束

• 批准号: 1220075
• 负责人: James Hirth
• 金额: $ 29.19万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-07-15 至 2016-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1220075&HistoricalAwards=false
• 关键词: Experimental; Constraints; Crustal; Rheology

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.

下大陆壳的流变控制了广泛的过程，这些过程对于理解板边界剪切区的发展和演变很重要长期支持山带。尽管描述下层岩石岩石流动行为的现有法律可以解释许多地质观察，但是将这些法律推断到适合下大陆地壳的条件表明，通过新的实验数据可以改善地球物理和地质衍生数据的解释。该项目的目的是在适合下大陆壳的压力下提供有关岩石流变学的新实验数据。该项目将涉及三条研究线，其中涉及在GRIGGS和PATERSPM变形设备中进行的一组实验，在900至1100摄氏度的温度下，以及在500 MPa至1.5 GPA的限制压力下应变。这些实验将解决以下内容：（1）水对下地壳岩石的流变/粘度的作用。最初的工作表明，随着水含量的增加，糖尿病酶粘度的急剧变化。这些结果将扩展到更高的温度/较低应力，以增加外推到自然条件的分辨率。 （2）动态重结晶和岩石织物（即，晶格首选）在斜长石中的发展。初始实验工作的结果基于对自然变形岩石的分析来挑战以前的解释。但是，从表面上看，自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晶粒尺寸的演变，并更好地理解斜长石中的晶格首选方向发展。 （3）闪石的流变学。关于闪石流变性的实验很少，尽管它对地壳中至下壳剪切区中的地壳流变学和无处不在的存在重要性。由于其热稳定性有限，因此缺乏数据部分反映了实验室中闪石变形的困难。由自然岩石中的微观结构激励，研究人员将使用非常细粒的聚集体来探索低应激变形过程在闪石中的作用，这是一种新方法。了解下层地壳的流变特性对于广泛的地球动力问题很重要。理解地壳流变学的最重要原因可能是为了准确评估通过时间依赖性地震源性断层产生的地震危害 - 可以通过大地研究来量化。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状态，它们弥合了材料科学与地质科学之间的差距。该项目的另一个组成部分将是创建Brown University Rock Mechanics实验室先前变形实验的可搜索档案。该档案将包含更多2000年实验的信息，涵盖了40多年的研究。访问此类数据库将有助于新的想法，并鼓励直接实验性岩石变形社区以外的科学家探索与他们自己的研究有关的流变学数据和随之而来的微观结构。