Comparison of the Melt Distribution in Natural Analogues to Experimentally Produced Microstructures

地球浅层地幔中熔体的产生，以及这种熔体在地球表面以玄武岩的形式分离和喷发，是地球继续演化的主要过程。在熔融过程中，低熔点组分与难熔组分分离，后者留在地幔中。与玄武岩熔体一起输送到地表的低熔点组分包括水和二氧化碳等挥发物。再加上俯冲作用，这种内部与表面的交换形成了地球生命中大气的组成。这一过程也构成了一系列构造环境中火山管道系统的最深部分。因此，了解深层融水迁移是了解火山动力学的一个组成部分。地幔中的过程，如熔体的产生，不能直接观察到，但可以通过实验和研究地球表面地幔岩石的自然发生来询问。该项目将检测的天然岩石在微观结构和成分方面相对罕见。初步观测表明，玄武岩熔体在地幔起源的岩石中冻结，但具有通常只在实验中观察到的间隙熔体几何形状。因此，这些岩石在实验、野外直接观测和间接观测方法（如部分熔融区域的地震成像）之间形成了重要的联系。本项目旨在验证上地幔条件下小样本实验结果在自然系统不同时空尺度上的应用，从而更好地理解熔体产生和输送过程。为此，我们将通过光学和扫描电子显微镜检查富含橄榄石的橄榄岩薄片，并收集电子后向散射衍射图。这些地图和图像将以同样的方式处理，从实验产生的样品中提取图像，以量化颗粒尺度上的熔体分布。微探针和激光烧蚀质谱分析将有助于阐明形成微观结构的过程。

The generation of melt in the Earth's shallow mantle, and the segregation and eruption of this melt at the Earth's surface as basalt is the main process by which the Earth continues to evolve. During melting low melting point components are separated from more refractory components, which remain behind in the mantle. The low melting point components transported to the surface with the basaltic melt include volatiles such as water and CO2. Together with the process of subduction, this exchange of the interior with the surface has shaped the composition of the atmosphere over the life of the Earth. This process also constitutes the deepest part of the plumbing systems of volcanoes in a range of tectonic settings. Understanding deep melt migration is therefore an integral part of understanding the dynamics of volcanoes.Processes in the mantle such as the generation of melt can not be observed directly, but are interrogated experimentally as well as by studying natural occurrences of mantle rocks at the Earth's surface. The natural rocks that will be examined for this project are relatively rare in terms of their microstructure and composition. Preliminary observations indicate that a basaltic melt froze in place in rocks of mantle origin, but with an interstitial melt geometry normally observed only in experiments. Thus these rocks form an important link between experiments, direct observations in the field and indirect methods of observation such as seismic imaging of partially molten regions. This project is intended to help validate the application of experimental results on small samples at upper mantle conditions to the different scales in space and time of natural systems, leading to a better understanding the process of melt generation and transport. To this end we will examine thin sections of olivine-rich troctolites by optical and scanning electron microscopy, and collect electron-backscatter diffraction maps. Together these maps and images will be processed in the same way that images from experimentally produced samples are processed to quantify the melt distribution on the grain scale. Additional analysis by microprobe and laser-ablation mass spectrometry will help illuminate the processes that formed the microstructures.