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，那里的碳酸盐岩中经常发现剪切带。许多野外研究表明，局部化伴随着岩石结构的显著变化，如粒度、晶格(晶体)择优取向、主相和副相化学、孔隙几何和相分散等方面。以往的实验室研究表明，蠕变强度在很大的应变区间内变化，并且晶粒度、晶形和晶格择优取向同时演化。最近的工作还表明，再结晶动力学与变形过程中的功的速率成比例，晶格择优取向受辅助相的形状和弥散参数的强烈影响，而镁固溶体既影响晶界的迁移率，也影响从扩散到位错蠕变的转变。为了了解在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。该项目将与英国利物浦大学和曼彻斯特大学的工作人员合作，观察瑞士阿尔卑斯山剪切带碳酸盐岩中的变形微结构，以及实验室中变形的样品中的微结构。在应变速率为10^-2-10^-6^-1，围压小于300兆帕，温度在500-1000 K之间的情况下，力学测试将包括天然大理石和合成大理石的简单剪切、扭转和常规三轴加载。两种新技术--微观应变作图和高剪切应变下的顺序微观分析--将被用来了解应变在不同变形机制中的动力学和分配。通过结合深入的现场工作、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一些差距。除了增加对岩石构造和力学性质的了解外，实验室工作还将改进碳酸盐岩力学行为的数据库，这在提高石灰岩储层石油采收率、封存裂隙和沉积碳酸盐岩层中的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.