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

硬石膏岩石蠕变变形和退火过程中的微观结构演化和晶界迁移率。

• 批准号: NE/H001034/1
• 负责人: Elisabetta Mariani
• 金额: $ 9.69万
• 依托单位: University of Liverpool
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FH001034%2F1
• 关键词: Microstructure; evolution; grain; boundary; mobility

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.

硬石膏 (CaSO4) 在浅地壳中非常重要，可作为构造板块边界主要断层带的脱离层、碳氢化合物储层的盖层、二氧化碳封存以及放射性废物的潜在储存库。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。在材料的塑性变形（位错蠕变）和退火（静态加热）过程中，通过晶界的形成和移动，发生恢复和再结晶过程。在地壳和地幔中，岩石的同构造（动态）和构造后（静态）重结晶可以改变晶粒尺寸、形状和晶体取向。这会影响物理性质和各向异性，并且对于解释沿板块边界的主要断层带中的岩石的力学行为、山带中的地质地形和地震各向异性数据至关重要。一般而言，人们对硬石膏和矿物的重结晶行为和相关边界特性（几何形状、流动性、扩散性和滑动性）知之甚少。在以孪晶界（硬石膏、方解石、石英、斜长石）等特殊晶界为特征的矿物中，观察到的微观结构不能单独用亚晶旋转和晶界迁移再结晶来解释，人们提出了另外两种机制，即晶界滑动，同时伴随着晶界滑动。扩散并导致材料弱化和考虑特殊（孪生）边界的再结晶机制。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常常被抹杀。非标准变形和退火实验室实验，其中硬石膏骨料将分别采用小增量的应变和时间，并在每次增量后使用 EBSD 进行分析，以深入了解 1. 再结晶的动力学和运动学孪晶边界，2。它在硬石膏骨料和其他类似矿物的变形行为中所发挥的作用。此类测试是非标准的，因为将采用相​​同的样本，而不是像岩石变形测试中常规的不同样本，以增加应变或时间并顺序分析。这将允许在多晶材料的蠕变变形和退火过程中跟踪单个晶粒和晶界的演变。在每次变形实验期间，变形装置的高分辨率应变计将记录对特定微观结构变化的精细机械响应。将获得有关晶界几何形状、取向差、晶粒畸变、低角度和高角度晶界迁移的运动学、晶界迁移率、孪生作用以及对微观结构变化的机械响应的定量信息。在蠕变装置中测量的边界迁移率将与在扫描电子显微镜下的新型原位退火实验中直接观察边界运动获得的迁移率数据进行比较，作为该实验计划的一部分，该实验将在硬石膏上进行。将通过进行高围压实验并将结果与​​蠕变试验（室内压力）的结果进行比较来测试等静压对晶界流动性的重要影响。由此收集到的关于硬石膏多晶微观结构变化的再结晶机制、流动性和机械响应的证据将成为构建更现实的再结晶模型的基础。这将支持我们对地壳和地幔的同构造和后构造过程的解释。

项目成果

Characterization of microstructures and interpretation of flow mechanisms in naturally deformed, fine-grained anhydrite by means of EBSD analysis

通过 EBSD 分析表征自然变形细粒硬石膏的微观结构并解释流动机制

• DOI: http://dx.10.1144/sp360.14
• 发表时间: 2022
• 期刊: Geological Society, London, Special Publications
• 作者: Hildyard R