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

在地球浅层地幔中熔融的产生，以及在地球表面作为玄武岩的熔融的分离和喷发是地球继续演化的主要过程。在熔融过程中，低熔点组分与留在地幔中的较难熔组分分离。随着玄武岩熔体输送到地表的低熔点成分包括挥发物，如水和二氧化碳。与俯冲过程一起，这种内部与表面的交换塑造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，了解深部熔体的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产状来进行询问。将为该项目检查的天然岩石在微观结构和成分方面相对罕见。初步观察表明，玄武岩熔体冻结在地幔成因的岩石中，但具有间隙熔体几何结构，通常只有在实验中才能观察到。因此，这些岩石构成了实验、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)之间的重要联系。该项目的目的是帮助验证在上地幔条件下对小样本的实验结果在自然系统的不同空间和时间尺度上的应用，从而更好地理解熔体的产生和传输过程。为此，我们将用光学显微镜和扫描电子显微镜观察富含橄榄石的沸石薄片，并收集电子背向散射衍射图。这些地图和图像将以相同的方式处理，就像处理来自实验产生的样品的图像以量化颗粒尺度上的熔体分布一样。用微探针和激光烧蚀质谱仪进行的额外分析将有助于阐明形成微结构的过程。

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.