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。已经推测了410公里附近可能的熔融及其对地球化学循环的影响。然而，对于深部上地幔条件下的部分熔融条件，目前还没有明确的研究。因此，临界含水率存在很大的不确定性。在这项提案中，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率。部分熔融的临界含水率是了解深水循环的关键参数，包括洋体的起源和演化以及控制上地幔含水率的过程。在这个项目中，我们将使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来解释地幔中电导率随温度和水分的分布。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。我们预计，部分熔化的开始将极大地改变电导率，因此，通过测量电导率，我们应该能够检测到少量的部分熔化。实验将在P(压力)=4-16 Gpa，T(温度)=1000-1900K的条件下，用多面顶压机的阻抗谱进行。部分熔化将通过电导率的跳跃和微量元素浓度的变化来检测。这些结果对深部地幔水循环以及电导率的解释具有重要意义。

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.