Determination of water partition coefficients between upper mantle minerals and melts as a function of pressure, temperature, and CO2 content using a rapid quench cell in multi-anvil experiments

在多砧实验中使用快速淬火室确定上地幔矿物和熔体之间的水分配系数作为压力、温度和 CO2 含量的函数

• 批准号: 402695659
• 负责人: Professor Dr. Tomoo Katsura
• 金额: --
• 依托单位: Bayerisches Forschungsinstitut für Experimentelle Geochemie und Geophysik (BGI)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/402695659?language=en
• 关键词: Determination; water; partition; coefficients; between

It is commonly accepted that the Earth’s mantle contains trace amounts of water varying from 10^(1) to 10^(3) wt. ppm in different regions. However, the question about how water is distributed and cycled in the earth interior remains. Although the behaviors of water in the shallow part of upper mantle are already well constrained by natural sampling, those in the deep asthenosphere are still under debate due to the lack of natural samples. Knowledge about water partitioning between minerals and basaltic melts under asthenosphere conditions is the key for understanding the water behavior in the mantle. In spite of that a series of experimental studies about water partition coefficients between the major upper mantle minerals (olivine and pyroxene) and melts have been reported, all of those data are based on experiments performed at pressures below 4 GPa, corresponding to lithosphere or topmost asthenosphere conditions. The water partitioning in the deep asthenosphere (up to 13 GPa) is unknown since it should be pressure-dependent inferred from the significant pressure dependence of water solubility in olivine. The reason for the limited pressure condition is that basaltic melts cannot be quenched to glass in a typical multi-anvil or piston-cylinder experiment at higher than 4 GPa, and therefore impossible to directly measure the water contents in melts, sequentially, unable to determine the water partition coefficients between minerals and melts.In order to investigate the water partitioning between upper mantle minerals and basaltic melts at high pressures corresponding to those in the deep asthenosphere, in this study, we will design a multi-anvil cell assembly with much faster quenching rate (here called “rapid quench cell”) than typical multi-anvil experiments to quench the basaltic melts to glass at high pressures. By directly measuring the water contents in the glass and coexisted forsterite and enstatite, their water partition coefficients will be obtained as a function of pressure from 1 to 13 GPa, temperature from 1300 to 1900 K. The preliminary experiments demonstrated that melt coexisting with olivine can be quenched from 1870 K at a pressure of 8 GPa, and implied a possibility that the previous study might misinterpreted the pressure and/or temperature dependence of the partition coefficients. Additionally, since CO2 content in melts may significantly affect the water partitioning, the CO2-content dependence of water partition coefficients will also be investigated.

人们普遍认为，地幔中含有微量的水，其含量从10^（1）到10^（3）wt.不等。在不同地区的ppm。然而，关于水在地球内部如何分布和循环的问题仍然存在。虽然上地幔浅层的水行为已经得到了天然样品的很好的约束，但由于缺乏天然样品，深部软流圈的水行为仍存在争议。软流圈条件下水在矿物和玄武岩熔体之间的分配是理解地幔水行为的关键。尽管已经报道了一系列关于上地幔主要矿物（橄榄石和辉石）和熔体之间的水分配系数的实验研究，但所有这些数据都是基于在低于4GPa的压力下进行的实验，对应于岩石圈或最顶部的软流圈条件。在深软流圈（高达13 GPa）的水分配是未知的，因为它应该是压力依赖性从橄榄石中的水溶解度显着的压力依赖性推断。限制压力条件的原因是玄武岩熔体在高于4GPa的典型多砧或活塞-圆筒实验中不能淬火成玻璃，因此不可能直接测量熔体中的水含量，为了研究高压下上地幔矿物与玄武岩熔体之间的水分配，在这项研究中，我们将设计一个多砧室组件，其淬火速率比典型的多砧实验快得多（这里称为“快速淬火室”），以在高压下将玄武岩熔体淬火成玻璃。通过直接测量玻璃及共存镁橄榄石和顽火辉石中的水含量，得到了它们的水分配系数随压力（1 ~ 13 GPa）和温度（1300 ~ 1900 K）的变化关系。初步的实验表明，熔体共存的橄榄石可以淬火从1870 K在8 GPa的压力，并暗示了一种可能性，以前的研究可能会误解的压力和/或温度依赖性的分配系数。此外，由于熔体中的CO2含量可能会显着影响水分配系数的CO2含量的依赖性也将被调查。