CSEDI Collaborative Research: Optical investigations of a mantle plume laboratory model

地幔内地幔柱的概念在将深部地幔对流与火山活动、地形隆起和地球化学特征的地表表现联系起来方面发挥了核心作用。然而，这个概念仍然不完整。为了完善我们对地幔柱及其在地球动力学和地球化学演化中的作用的理解，还有两个问题有待解决。第一个，也是激烈争论的主题，是在内部加热的对流地幔中羽流的存在和生存，该地幔由与板块运动有关的大规模流动主导。二是洋岛玄武岩同位素特征揭示的地球化学变化程度，我们认为这是地幔柱的地表表现。为了解决这两个问题，PIs Lithgow-Bertelloni, Cotel， Whitehead和Hart正在对均匀和分层流体中的单一热羽流和成分羽流进行实验室实验。本实验的主要目标是，首先，准确测量和表征整个演化羽流的浮力通量作为初始热通量和流体成分的函数，其次，分析大尺度环流引起的剪切对羽流破裂和导管内搅拌的影响。重点在于使用新的非侵入式光学技术（粒子图像测速、激光诱导荧光、光偏转和用于数字粒子图像测温的热致变色液晶）。这些仪器除了可以同时测量成分和温度外，还可以直接测量三维流动结构。在接下来的三年里，pi计划提供严格的尺度关系，以阐明-导致稳定羽流和稳定状态管道或上升时羽流破裂的条件-与地震成像相关的羽流结构的时空变化-携带物质在热和热化学羽流中存活和相互作用的尺度-与海洋岛屿玄武岩的同位素地球化学变异的联系。获得资助的项目涉及四个具有从地球物理流体动力学到地球化学等广泛不同科学和技术专门知识的pi之间的密切合作。因此，这些实验的结果可能会引起地球科学界不同部门的兴趣。所有四个pi都参与实验设计和结果解释。

The concept of plumes within the mantle of the earth has played a central role in linking deep mantle convection to surface expressions of volcanism, topographic uplift, and geochemical signatures. However, the concept continues to remain incomplete. Two issues remain to be resolved to complete our understanding of mantle plumes and their role in the dynamical and geochemical evolution of the planet. The first, and the subject of vigorous controversy, is the very existence and survival of plumes in an internally heated, convecting mantle dominated by the large-scale flow associated with plate motions. The second relates to the degree of geochemical variation revealed by the isotopic signatures of ocean island basalts, which we identify as the surface expression of mantle plumes.In order to address both issues, PIs Lithgow-Bertelloni, Cotel, Whitehead and Hart are conducting laboratory experiments on single thermal and compositional plumes in homogeneous and stratified fluids. The primary goals of the present experiments are first, to accurately measure and characterize the buoyancy flux throughout an evolving plume as a function of the initial heat flux, and fluid composition, and second, to analyze the effects of shearing induced by the large-scale circulation on plume breakup and on stirring within the conduit. The emphasis lies in the use of new non-intrusive optical techniques (Particle Image Velocimetry, Laser-Induced Fluorescence, light deflection, and thermochromic liquid crystals for Digital Particle Image Thermometry). These can directly measure the three-dimensional flow structure in addition to giving the simultaneous measurements of composition and temperature. Over the next three years the PIs intend to provide rigorous scaling relationships to illuminate - The conditions that lead to steady plumes and steady-state conduits or plume breakup upon ascent- Spatial and temporal variations in plume structure as it relates to seismic imaging- The scales at which entrained material survives and interacts in thermal and thermochemical plumes- The link with the isotopic geochemical variability of ocean island basalt.The funded project involves close collaboration between four PIs with widely varying scientific and technical expertise ranging from geophysical fluid dynamics to geochemistry. Hence, the results of these experiments are likely to be of interest to diverse segments of the Earth Sciences community. All four PIs are involved in the experimental design and interpretation of the results.