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

应变局部化在地壳造山带中很常见，在碳酸盐岩中经常发现剪切带。许多实地研究表明，局部化伴随着岩石结构的显著变化，如粒度、晶格（晶体学）优选取向、主相化学和副相化学、孔隙几何形状和相色散。先前的实验室研究表明，蠕变强度在大的应变区间内发生变化，晶粒尺寸、晶粒形状和晶格优先取向同时发生变化。最近的研究还表明，再结晶的动力学与变形过程中所做的功的速率成比例，晶格优先取向可能受到副相的形状和分散参数的强烈影响，Mg固体溶质影响晶界迁移率和从扩散到位错蠕变的转变。为了理解自然变形过程中强度的局部化和演化，必须知道每种效应的大小和候选机制的相对动力学。该项目将观察瑞士阿尔卑斯山剪切带碳酸盐岩的变形微观结构，以及在实验室变形的样品，并与英国利物浦大学和曼彻斯特大学的工作人员合作。机械测试将包括在应变率为10^-2-10^-6 ^-1、围压小于300 MPa、温度在500-1000 K之间的条件下，对天然大理石和合成大理石进行简单剪切、扭转和常规三轴加载。两种新技术，微应变映射和高剪切应变下的序列微分析，将用于了解各种变形机制之间的动力学和应变分配。通过结合彻底的实地考察、仔细的实验和详细的观察，目的是弥合实验室研究和实地研究之间的一些差距。除了增加构造学和岩石力学性质的知识外，实验室工作还将改善碳酸盐岩力学行为的数据库，这在诸如提高石灰岩储层石油采收率、裂缝和沉积碳酸盐岩地层二氧化碳封存以及设计工程地下结构等工程应用中具有相当大的兴趣。

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.