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

在本项目中，我们将利用地球物理推断的地球上地幔电导率分布来推断上地幔的物理和化学条件。水在地幔中的分布反映了上地幔的演化过程。与海洋上地幔不同，大陆上地幔的演化鲜为人知。因此，我们将把注意力集中在大陆上地幔中水的分布上，并以此推断大陆的演化。基于一系列的实验（和理论）研究，卡拉托和他的同事们已经证明，水（氢）显著地增强了上地幔矿物的导电性。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。这些关系已经很好地建立起来，并表明水的影响比其他参数强得多。影响电导率的“其他参数”（主要元素组成、温度、氧逸度等）可以从其他观测（例如地幔样品的温度和主要元素组成）中推断出来。因此，我们可以通过这些观测的整合，从推断的电导率分布推断出水的分布。Kate Selway在分析MT数据以从电磁感应观测构建三维电导率分布方面具有丰富的经验。她最近从坦桑尼亚获得了新的数据集，但我们也将使用包括南非和北美在内的其他地区的数据。考虑到上面列出的“其他因素”的知识，我们将建立通过与MT数据比较来绘制水分布的方法。本研究将采用正演和逆演两种建模方法。在这项研究中，我们将对大陆上地幔的水分布有更好的了解，这将为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.