Predicting and explaining crystallographic orientation relationships of exsolved precipitates in garnet using the edge‐to‐edge matching model
Predicting and explaining crystallographic orientation relationships of exsolved precipitates in garnet using the edge‐to‐edge matching model
复制标题
DOI：
10.1111/jmg.12662
复制
发表时间：
2022-03
影响因子：
3.4
通讯作者：
D. S. Keller;J. Ague
中科院分区：
文献类型：
--
作者：
D. S. Keller;J. Ague
矿物出溶体与其主晶的相对排列可以用晶体学取向关系（COR）来描述。来自高级变质岩和火成岩的石榴石中的出溶相可能具有COR，但COR分布的复杂性迄今为止限制了它们用于识别出溶相。COR的分类也仍然是矿物特有的，这使得人们对COR保存的信息产生了疑问。为了测试COR如何标准化，我们计算了沉淀物和石榴石之间的低指数晶面（d值比）和晶体方向（原子行）的失配，并定义了可能在能量上有利的结构排列的搜索标准。我们分析了发表的电子背散射衍射（EBSD）数据的磷灰石，金红石，钛铁矿，石榴石（ntot = 1,296）和石英沉淀物的存在下，这些路线。我们的方法预测了88%至98%的所研究矿物的观察到的对齐，并且只需要使用晶胞参数进行计算。我们进一步表明，每种出溶矿物形成COR预测的边到边匹配模型，该模型是为了描述明确的出溶织构合金。边对边匹配通过具有相似间距的晶面的平行性或接近平行性以及这些平面边缘上具有相似长度的晶向（原子行）的平行性来对齐宿主-沉淀物界面处的原子。边到边匹配可能通过降低表面自由能和应变能、稳定沉淀物来促进共格到半共格界面。这些匹配由适用于所有矿物的标准定义，使其成为分类，发现和解释石榴石中各种沉淀物的COR的理想工具。该方法还可以预测其他地质矿物对中的COR（例如，脱溶的长石）。我们发现，边缘到边缘匹配可以解释通常观察到的石榴石出溶织构的针状形态的稳定性。边缘到边缘匹配的COR分布可以作为出溶时寄主岩石状态的代理进行测试，以评估温度、冷却速率、过冷度和/或应变等因素。边到边匹配的COR模式可以与地质温压法和/或岩石年代学配对，为研究麻粒岩相和榴辉岩相变质岩和火成岩的历史提供强有力的新工具。
Relative alignments of mineral exsolutions and their host crystals can be described by crystallographic orientation relationships (COR). Exsolved phases in garnet from high‐grade metamorphic rocks and igneous rocks may have COR, but the complexity of COR distributions has thus far restricted their use to identifying exsolved phases. Classification of COR also remains mineral‐specific, leaving doubt as to what information COR preserve. To test how COR may be standardized, we calculated mismatch of low‐index crystallographic planes (d‐value ratios) and crystallographic directions (rows of atoms) between precipitates and garnet and defined search criteria for structural alignments likely to be energetically favourable. We analysed published electron backscatter diffraction (EBSD) data for apatite, rutile, ilmenite, corundum, and quartz precipitates in garnet (ntot = 1,296) for the presence of these alignments. Our method predicts between 88% and 98% of observed alignments across the studied minerals and requires only calculations using unit cell parameters. We further show that each exsolved mineral forms COR predicted by the edge‐to‐edge matching model which was developed to describe unambiguous exsolution textures in alloys. Edge‐to‐edge matching aligns atoms at the host–precipitate interface by parallelism or near‐parallelism of crystallographic planes of similar spacing and parallelism of crystallographic directions (rows of atoms) of similar length on the edges of those planes. Edge‐to‐edge matches likely facilitate coherent to semi‐coherent interfaces by lowering surface free energy and strain energy, stabilizing precipitates. These matches are defined by criteria applicable to all minerals, making them an ideal tool for classifying, discovering and interpreting COR of diverse precipitates in garnet. This approach may also predict COR in other geological mineral pairs (e.g., exsolved feldspars). We find that edge‐to‐edge matching may explain the stability of the needle‐shaped morphologies commonly observed for exsolution textures in garnet. Edge‐to‐edge matching COR distributions can be tested as proxies of the state of the host rock at the time of exsolution to evaluate factors such as temperature, cooling rate, degree of undercooling, and/or strain. Patterns of edge‐to‐edge matching COR may be paired with geothermobarometry and/or petrochronology to provide a powerful new tool for studying the histories of granulite and eclogite facies metamorphic and igneous rocks.