CSEDI: Understanding the structure of the continental upper mantle through the use of magnetotelluric and seismic observations

本计画将利用地球上地幔的电导率分布来推测上地幔的物理化学条件。水在地幔中的分布反映了上地幔的演化过程。与大洋上地幔不同的是，大陆上地幔的演化还知之甚少。因此，我们将把注意力集中在大陆上地幔水的分布，我们推断大陆的演化。基于一系列的实验（和理论）研究，Karato和他的同事们已经证明，水（氢）显着增强上地幔矿物的电导率。这些实验研究建立了电导率，含水量，温度，氧逸度等之间的函数关系。这些关系是很好地建立，并表明，水的影响比其他参数强得多。适度影响电导率的“其他参数”（主要元素成分、温度、氧逸度等）可以从其他观测（例如，温度和地幔样品的主要元素组成）推断。因此，我们可以通过这些观测结果的整合，从推断的电导率分布中推断水的分布。Kate Selway博士在分析MT数据以根据电磁感应观测结果构建三维电导率分布方面拥有丰富的经验。她最近从坦桑尼亚获得了新的数据集，但我们也将使用其他地区的数据，包括南非和北美。鉴于上述“其他因素”的知识，我们将通过与MT数据的比较，建立绘制水分布图的方法。在这项研究中，将使用正向和反向建模方法。在这项研究中，我们将更好地了解大陆上地幔的水分布，这将对大陆如何生长提供重要的见解。

In this project, we will use geophysically inferred electrical conductivity distribution of the Earth's upper mantle to infer the physical and chemical conditions of the upper mantle. The distribution of water in the mantle reflects the processes by which the upper mantle has evolved. Unlike the oceanic upper mantle, evolution of the continental upper mantle is poorly understood. Consequently, we will focus our attention to the distribution of water in the continental upper mantle from which we infer the evolution of continents. Based on the series of experimental (and theoretical) studies, Karato and his co-workers have shown that water (hydrogen) enhances electrical conductivity of upper mantle minerals dramatically. These experimental studies established the functional relationship between electrical conductivity, water content, temperature, oxygen fugacity etc. These relationships are well established and show that the influence of water is much stronger than other parameters. 'Other parameters' that affect electrical conductivity modestly (major element composition, temperature, oxygen fugacity etc.) can be inferred from other observations (temperature and major element composition from mantle samples, for example). Consequently, we can infer the water distribution from the inferred electrical conductivity distribution through the integration of these observations.Dr. Kate Selway has extensive experience in analyzing the MT data to construct three-dimensional conductivity distributions from the observations of electromagnetic induction. She has recently obtained new data set from Tanzania, but we will also use the data from other regions including South Africa and North America. Given the knowledge of 'other factors' listed above, we will establish the methodology to map out water distribution by comparison to MT data. Both forward and inverse modeling approaches will be used in this study. For this study, we will have a better understanding of water distribution in the continental upper mantle that will shed important insights into how continents might have grown.