Microstructure evolution and grain boundary mobility during creep deformation and annealing of anhydrite rocks.

硬石膏（CaSO 4）在地壳浅层中作为构造板块边界主要断裂带的拆离层、油气藏的盖层、CO2封存和放射性废物的潜在储存库是重要的。硬石膏也是一种有用的硅酸盐类似材料，其物理性质与其他类似矿物的流变学和重结晶有关。回复和再结晶过程发生在材料的塑性变形（位错蠕变）和退火（静态加热）期间，通过晶界的形成和移动。在地壳和地幔中，岩石的同构造（动态）和构造后（静态）重结晶可以改变粒度、形状和晶体学取向。这会影响物理性质和各向异性，并且对于解释沿着板块边界的主要断裂带中岩石的力学行为、山区地质地形和地震各向异性数据至关重要。硬石膏和矿物的重结晶行为和相关的边界性质（几何形状，流动性，扩散性和滑动）一般，知之甚少。在以特殊边界为特征的矿物中，如孪晶边界（硬石膏、方解石、石英、斜长石），观察到的微观结构不能单独用亚晶粒旋转和边界迁移重结晶来解释，已经提出了另外两种机制，即晶界滑动，伴随着扩散并导致材料弱化，以及重结晶机制解释特殊（孪晶）边界。这发生在相对高应力下的晶体塑性变形期间。在自然和实验变形岩石的最终微观结构中，微观结构演化的详细证据以及驱动它的机制往往被抹去。非标准变形和退火实验室实验，其中硬石膏骨料将分别以应变和时间的小增量进行，并且在每个增量之后，使用EBSD进行分析，以深入了解1。孪晶界辅助再结晶的动力学和运动学; 2.这在硬石膏集合体和其他类似矿物的变形行为中所起的作用。这些测试是非标准的，因为相同的样品，而不是岩石变形测试中传统的不同样品，将被带到应变或时间的增量，并依次进行分析。这将允许在多晶材料的蠕变变形和退火期间跟踪单个晶粒和晶界的演变。在每个变形实验期间，对特定微观结构变化的精细机械响应将由变形装置的高分辨率应变计记录。将获得关于边界几何形状、取向差、晶粒变形、低角度和高角度晶界迁移的运动学、晶界流动性、孪晶的作用以及对微观结构变化的机械响应的定量信息。在蠕变台测量的边界流动性进行比较，从直接观察边界运动在新的原位退火实验在扫描电子显微镜，这将是硬石膏作为本实验计划的一部分进行的流动性数据。通过高围压实验，并与蠕变台架试验（室内压力）的结果进行比较，将检验等静压对晶界流动性的重要影响。因此，收集的证据上的重结晶机制，流动性和机械响应的硬石膏多晶体的微观结构变化将是基础上，更现实的重结晶模型可以构建。这将支持我们对地壳和地幔中的同构造和后构造过程的解释。

Anhydrite (CaSO4) is important in the shallow Earth's crust as a detachment horizon in major fault zones at tectonic plate boundaries, cap-rock for hydrocarbon reservoirs, CO2 sequestration, and potential repository for radioactive waste. Also anhydrite is a useful silicate-analogue material and its physical properties are relevant to the rheology and recrystallization of other comparable minerals. Recovery and recrystallization processes occur during plastic deformation (dislocation creep) and annealing (static heating) of materials, through the formation and movement of grain boundaries. In the Earth's crust and mantle syn-tectonic (dynamic) and post-tectonic (static) recrystallization of rocks can modify grain sizes, shapes and crystallographic orientations. This affects physical properties and anisotropies and is central to the interpretation of the mechanical behaviour of rocks in major fault zones along plate boundaries, geological terrains in mountain belts, and seismic anisotropy data. The recrystallization behaviour and relevant boundary properties (geometry, mobility, diffusivity and sliding) of anhydrite and minerals in general, are poorly understood. In minerals characterized by special boundaries such as twin boundaries (anhydrite, calcite, quartz, plagioclase), observed microstructures cannot be explained by sub-grain rotation and boundary migration recrystallization alone and two other mechanisms have been proposed, namely grain boundary sliding, accompanied by diffusion and resulting in material weakening and a recrystallization mechanism accounting for special (twin) boundaries. This occurs during crystal plastic deformation at relatively high stresses. In the final microstructures of naturally and experimentally deformed rocks detailed evidence of microstructural evolution, and the mechanisms that drive it, is often obliterated. Non-standard deformation and annealing laboratory experiments, where anhydrite aggregates will be taken to small increments of strain and time respectively and, after each increment, analysed using EBSD, will be performed to gain insight into 1. The dynamics and kinematics of recrystallization assisted by twin boundaries, 2. The role that this plays in the deformation behaviour of anhydrite aggregates and other comparable minerals. Such tests are non-standard because the same sample, rather than different ones as is conventional in rock deformation tests, will be taken to increments of strain or time and sequentially analysed. This will allow tracking the evolution of individual grains and grain boundaries during creep deformation and annealing of a polycrystalline material. During each deformation experiment the fine mechanical response to specific microstructural changes, will be recorded by the high resolution strain gauges of the deformation apparatus. Quantitative information on boundary geometry, misorientation, grain distortion, kinematics of low and high angle grain boundary migration, grain boundary mobility, the role of twinning, and mechanical response to microstructural change will be achieved. Boundary mobility measured in the creep rig will be compared with the mobility data obtained from direct observation of boundary motion in novel in-situ annealing experiments in the scanning electron microscope, which will be performed on anhydrite as part of this experimental program. The important effect of isostatic pressure on grain boundary mobility will be tested performing high confining pressure experiments and comparing results with those from creep rig tests (room pressure). The evidence thus gathered on recrystallization mechanisms, mobility and mechanical response to microstructural changes of anhydrite polycrystals will be the basis upon which more realistic recrystallization models can be constructed. This will underpin our interpretation of syn- and post-tectonic processes in the Earth's crust and mantle.