Electrical conductivity of synthetic pyrolite under deep upper mantle and transition zone conditions

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的，该项目的目的是提供一组新的实验室数据，以了解深部地幔水循环。推测了410 km附近可能的熔融及其对地球化学循环的影响。然而，在深部上地幔条件下，部分熔融的条件还没有确定的研究。因此，临界含水量存在很大的不确定性。在这一提议中，我们的工作重点是确定410公里深度附近部分融化的临界含水量。部分熔融的临界含水量是理解大洋深部水循环的一个重要参数，包括大洋的起源和演化以及控制上地幔含水量的过程。在本项目中，我们将利用电导率来确定部分熔融的开始，因此，这项工作的结果也将提供一个关键的新数据集，以解释电导率在地幔温度和含水量方面的分布。涉及水的部分熔融的条件很难通过实验确定。我们将通过测量电导率来研究水+橄榄岩体系的相图。我们预期部分熔化的开始将显著地改变电导率，因此通过测量电导率，我们应该能够检测到小程度的部分熔化。实验将在压力P =4-16 GPa，温度T = 1000-1900 K的条件下用多砧装置进行。部分熔化将通过电导率的跳跃以及微量元素浓度的变化来检测。研究结果对地幔深部水循环和电导率解释具有重要意义。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5) The purpose of this projects is to provide a new set of laboratory data to understand the deep mantle water cycling. Possible melting near the 410-km and its consequence on geochemical cycling have been speculated. However, there have been no definitive studies on the conditions for partial melting under the deep upper mantle conditions. Consequently there have been large uncertainties on the critical water content. In this proposal, our efforts are focused on determining the critical water content for partial melting near 410-km depth. The critical water content for partial melting is a critical parameter to understand the deep water cycling including the origin and evolution of the ocean mass and the processes to control the water content in the upper mantle. In this project, we will use electrical conductivity to determine the onset of partial melting and consequently, the results of this work will also provide a critical new data set to interpret the distribution of electrical conductivity in terms of temperature and water content in the mantle.The conditions for partial melting involving water are difficult to determine experimentally. We will investigate the phase diagram of water + peridotite system by measuring electrical conductivity. we anticipate that the onset of partial melting will dramatically change the conductivity and consequently, by measuring the electrical conductivity, we should be able to detect a small degree of partial melting. Experiments will be conducted using an impedance spectroscopy with a multianvil apparatus under the conditions of P (pressure) =4-16 GPa, and T (temperature) = 1000-1900 K. The partial melting will be detected by a jump in conductivity as well as the change in the trace element concentrations. The results have an important implication for the deep mantle water cycling as well as the interpretation of electrical conductivity.