CSEDI:Collaborative Research: Experimental and SIMS investigation of H2O storage capacity of the mantle

该项目是明尼苏达大学的实验岩石学家和亚利桑那州立大学的分析地球化学家之间的合作，旨在解决CSEDI计划的两个主要目标：(1)了解地球的深层水循环；(2)了解H2O对熔融、相变和地幔物理特性的影响。利用明尼苏达大学的高温高压装置进行上地幔、过渡带和下地幔条件下橄榄岩储水能力的实验。储水量是指在一定温度和压力下，固体橄榄岩所能保留的最大水容量。储水能力限制了富氢地幔储层的可能区域和可能的水熔融位置。由于H2O对地幔蠕变强度、弹性和电导率等性质的影响很大，它们也为地幔动力学提供了关键约束。实验产品将在亚利桑那州立大学使用新开发的低空白二次离子质谱技术分析微量水。本文将解决四个相关的实验问题：(1)为了研究最近的迹象，即上地幔具有比以前认为的更大的储存能力，在3-13千兆帕斯卡的实验中将确定橄榄岩的水储存能力。(2)为了确定水对洋脊和洋岛深层熔融的影响以及对上地幔脱水的影响，将在3-8 GPa测定矿物/熔体水的分配。(3)为了更好地了解水在410 km间断区内的输运，包括水对熔融和相变的影响，将在13-15 GPa温度范围内测定水的矿物间分配和储存容量。(4)为了解决关于下地幔储层能力的争议，将在670 km不连续区域的22 ~ 25 GPa压力下进行实验。

This project is a collaboration between experimental petrologists at U. Minnesota and analytical geochemists at Arizona State to address two of the chief goals of the CSEDI initiative: (1) to understand the Earth's deep water cycle and (2) to understand the influence of H2O on melting, phase transitions, and physical properties of the mantle. Experiments to determine the H2O storage capacity of peridotite under upper mantle, transition zone, and lower mantle conditions will be performed using high temperature high pressure devices at the University of Minnesota. The storage capacity is the maximum H2O that can be retained in solid peridotite at a given temperature and pressure. Storage capacities constrain possible regions of H2O-rich mantle reservoirs and possible loci of hydrous melting. Owing to the large effect of H2O on mantle properties such as creep strength, elasticity, and conductivity, they also provide critical constraints on mantle dynamics. Experimental products will be analyzed at Arizona State for trace quantities of H2O using newly-developed low-blank secondary ion mass spectrometry techniques. Four related experimental problems will be addressed: (1) To investigate recent indications that the upper mantle has a larger storage capacity than previously appreciated, experiments at 3-13 Gigapascals will determine peridotite H2O storage capacities. (2) To determine the influence of H2O on deep melting beneath oceanic ridges and oceanic islands and the consequences for dehydration of the upper mantle, mineral/melt H2O partitioning will be determined at 3-8 GPa. (3) To better understand transport of H2O across the 410 km discontinuity, including the effect of H2O on melting and phase transitions, inter-mineral partitioning of H2O and the storage capacity will be determined at 13-15 GPa over a range of temperatures. (4) To help resolve controversy about the storage capacity of the lower mantle, experiments will be performed at 22-25 GPa, pressures relevant to in the region of the 670 km discontinuity.