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。许多现场研究表明，局部化伴随着岩石结构等方面的显着变化，如晶粒尺寸、晶格（晶体学）择优取向、主相和副相化学、孔隙几何形状和相分散。先前的实验室研究表明，蠕变强度在较大的应变间隔内发生变化，并且晶粒尺寸、晶粒形状和晶格择优取向同时变化。最近的研究还表明，再结晶动力学与变形过程中所做的功速率成比例，晶格择优取向可能受到辅助相的形状和色散参数的强烈影响，并且镁固溶体影响晶界迁移率以及从扩散到位错蠕变的转变。为了了解自然变形过程中强度的定位和演变，必须知道每种效应的大小和候选机制的相对动力学。该项目将与英国利物浦大学和曼彻斯特大学的工作人员合作，观测瑞士阿尔卑斯山剪切带碳酸盐岩的变形微观结构，以及实验室变形样品的变形微观结构。机械测试将包括天然和合成大理石的简单剪切、扭转和传统三轴载荷，应变率为 10^-2-10^-6 ^-1，围压小于 300 MPa，温度在 500-1000 K 之间。微应变映射和高剪切应变下的顺序微分析这两种新技术将用于了解各种变形机制之间的动力学和应变分配。实地考察、仔细的实验和详细的观察，目的是弥合实验室和实地研究之间的一些差距。除了增加对岩石的构造和力学特性的了解外，实验室工作还将完善碳酸盐岩力学行为的数据库，这些数据库在提高石灰岩储层中的石油采收率、在裂缝和沉积碳酸盐地层中封存二氧化碳以及设计工程地下结构等工程应用中具有相当大的意义。

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.