Microstructure in Marble: Evolution of Strength in Natural and Laboratory Deformation

应变局部化现象在地壳造山带中很常见，剪切带常出现在碳酸盐岩中。许多现场研究表明，本地化是伴随着显着的变化，在这些方面的岩石结构的晶粒尺寸，晶格（晶体学）择优取向，主要和辅助相化学，孔隙几何形状，和相分散。以前的实验室研究表明，蠕变强度的变化在很大的应变间隔，晶粒尺寸，晶粒形状，晶格择优取向演变的同时。最近的工作还表明，再结晶的动力学缩放与在变形过程中所做的工作的速率，晶格择优取向可以强烈影响的形状和分散参数的辅助相，和镁固体溶质影响晶界流动性和从扩散到位错蠕变的过渡。为了了解自然变形过程中强度的局部化和演化，必须知道每个效应的大小和候选机制的相对动力学。该项目将对来自瑞士阿尔卑斯山剪切带的碳酸盐岩中的变形微观结构进行观察，并与英国利物浦大学和曼彻斯特大学的工作人员合作，对实验室中变形的样品进行观察。力学试验将包括天然和合成大理石在应变率为10^-2-10^-6 ^-1、围压小于300 MPa和温度在500-1000 K之间时的简单剪切、扭转和常规三轴加载。两种新技术，微观应变绘图，并在高剪切应变连续微观分析，将被用来了解动力学和应变之间的各种变形机制partitioning.By结合彻底的实地考察，仔细的实验，和详细的观察，目的是弥合实验室和现场研究之间的差距。除了增加岩石的构造和力学性质的知识，实验室工作将改善碳酸盐岩的力学行为的数据库，这是相当大的兴趣，在这样的工程应用，如提高采收率的石油在石灰岩油藏，二氧化碳封存在裂缝和沉积碳酸盐地层，并设计工程地下结构。

Strain localization is common in crustal orogenic belts, where shear zones are often found within carbonate rocks. Many field studies indicate that localization is accompanied by striking changes in such aspects of rock structure as grain size, lattice (crystallographic) preferred orientation, major and accessory phase chemistry, pore geometry, and phase dispersion. Previous laboratory studies indicate that creep strength changes over large intervals of strain, and that grain size, grain shape, and lattice preferred orientation evolve concurrently. Recent work also showed that the kinetics of recrystallization scaled with the rate of work done during deformation, that lattice preferred orientation could be strongly affected by the shape and dispersion parameters of accessory phases, and that Mg solid solutes influenced both grain-boundary mobility and the transition from diffusion to dislocation creep. In order to understand localization and evolution of strength during natural deformation, the size of each effect and the relative kinetics of the candidate mechanisms must be known. This project will make observations of deformation microstructure in carbonate rocks from shear zones in the Swiss Alps, and in samples deformed in the laboratory and in collaboration with workers at the Universities of Liverpool and Manchester, UK. Mechanical tests will include simple-shear, torsion, and conventional triaxial loading of natural and synthetic marbles at strain rates of 10^-2-10^-6 ^-1, confining pressures less than 300 MPa, and temperature between 500-1000 K. Two new techniques, microstrain mapping, and sequential microanalysis at high shear-strains, will be used to understand the kinetics and partitioning of strain amongst the various deformation mechanisms.By combining thorough fieldwork, careful experiments, and detailed observations, the aim is to bridge some of the gaps between laboratory and field studies. In addition to increasing knowledge of tectonics and mechanical properties of rocks, the laboratory work will improve the database for the mechanical behavior of carbonate rocks, which are of considerable interest in such engineering applications as enhanced recovery of oil in limestone reservoirs, sequestration of carbon dioxide in fractured and sedimentary carbonate formations, and designing engineered underground structures.