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

天然类似物与实验生产的微观结构的熔体分布比较

• 批准号: 1523027
• 负责人: Ulrich Faul
• 金额: $ 13.11万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-03-01 至 2017-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1523027&HistoricalAwards=false
• 关键词: Comparison; Melt; Distribution; Natural; Analogues

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.

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。在熔化过程中，低熔点成分与更难熔的成分分离，后者保留在地幔中。随玄武岩熔体输送到地表的低熔点成分包括水和二氧化碳等挥发物。与俯冲过程一起，内部与表面的这种交换塑造了地球生命周期中大气的成分。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，了解深层熔体迁移是了解火山动力学的一个组成部分。地幔中的过程（例如熔体的产生）无法直接观察到，但可以通过实验以及研究地球表面地幔岩石的自然发生来进行询问。该项目将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起源的岩石中，但具有通常仅在实验中观察到的填隙熔体几何形状。因此，这些岩石在实验、现场直接观测和间接观测方法（例如部分熔融区域的地震成像）之间形成了重要的联系。该项目旨在帮助验证上地幔条件下小样本的实验结果在自然系统不同空间和时间尺度上的应用，从而更好地了解熔体生成和运输过程。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方沸石薄片，并收集电子背散射衍射图。这些地图和图像的处理方式与处理实验生产的样品的图像的方式相同，以量化晶粒尺度上的熔体分布。通过微探针和激光烧蚀质谱进行的额外分析将有助于阐明形成微结构的过程。