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，地幔含有微量的水，重量从 10^(1) 到 10^(3) 不等。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。尽管上地幔浅层水的行为已经受到自然采样的很好约束，但由于缺乏自然样本，深层软流圈中的水的行为仍然存在争议。了解软流圈条件下矿物质和玄武岩熔体之间的水分配是了解地幔中水行为的关键。尽管已经报道了一系列关于主要上地幔矿物（橄榄石和辉石）与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 4 GPa 的压力下进行的实验，对应于岩石圈或最顶层的软流圈条件。深层软流圈（高达 13 GPa）中的水分配是未知的，因为从橄榄石中水溶性的显着压力依赖性推断它应该与压力相关。限制压力条件的原因是，在高于4 GPa的典型多砧或活塞缸实验中，玄武岩熔体无法淬火成玻璃，因此无法直接测量熔体中的水含量，进而无法确定矿物与熔体之间的水分配系数。 在深层软流圈中，在这项研究中，我们将设计一种多砧室组件，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。通过直接测量玻璃以及共存的镁橄榄石和顽火辉石中的水含量，可以获得它们的水分配系数，作为压力从1到13 GPa、温度从1300到1900 K的函数。初步实验表明，与橄榄石共存的熔体可以在8 GPa的压力下从1870 K开始淬火，这暗示了先前的研究可能误解了压力 和/或分配系数的温度依赖性。此外，由于熔体中的CO2含量可能显着影响水分配，因此还将研究水分配系数的CO2含量依赖性。