Experimental determination of the partition coefficient of water between phenocrysts and silicate melts in magma chambers.

决定火山活动方式的最重要因素之一是溶解在深处岩浆中的水量。水通过影响硅酸盐熔体相本身的性质和抑制岩浆的结晶程度来影响岩浆的粘度和密度。在岩浆喷发过程中，减压导致溶解的水溶解，形成气泡，将岩浆推向地表。水（和其他溶解气体）的数量和岩浆类型的化学成分之间的相互作用导致了从缓慢流动的熔岩（通常对人类没有危险）到快速移动的火山碎屑流的行为范围，这可能对火山周围的人口造成毁灭性的后果。因此，火山学家对确定历史喷发的岩浆库中的水量非常感兴趣，以便能够预测未来喷发的行为。有一系列方法可以分析火山爆发的产物，以估计爆发前的水浓度，但都有重要的局限性。本建议的目的是开发一种新方法，该方法依赖于测量溶解在火山岩晶体中的非常小的水浓度，然后使用这些值来计算喷发前岩浆中的水浓度。我们已经表明，可以使用红外光谱法测量晶体中的水浓度，现在我们希望进行实验来测量硅酸盐矿物和熔体之间的水分配。然后，我们将能够使用晶体中水的测量值来计算熔体相中的水浓度。如果成功的话，这个项目将允许获得更详细的岩浆挥发性演化的图片。

One of the most important factors in determining the way a volcano behaves is the amount of water dissolved in the magma at depth. Water influences the viscosity and density of the magma, both by affecting the properties of the silicate melt phase itself, and by suppressing the degree of crystallisation of the magma. During the eruption of the magma the reducing pressure causes the dissolved water to exsolve, forming bubbles which drive the magma to the surface. The interplay between the amount of water (and other dissolved gases) and chemical composition of the magma type causes the range of behaviour from slowly flowing lavas (which are not usually dangerous to humans), to rapidly moving pyroclastic flows which can have devastating consequences for populations around volcanoes. As a result, volcanologists are very interested in determining the amount of water in magma chambers of historic eruptions, to enable predictions of the behaviour of future eruptions to be made. There are a range of methods to analyse the products of volcanic eruptions to estimate pre-eruptive water concentrations, but all have important limitations. The aim of the present proposal is to develop a new method which relies on measuring the very small concentrations of water which are dissolved in the crystals of volcanic rocks, then to use these values to calculate the water concentration in the magma prior to eruption. We have already shown that it is possible to make measurements of the water concentrations of the crystals using infrared spectroscopy, we now wish to perform experiments to measure the partitioning of water between silicate minerals and melts. We will then be able to use our measured values of water in crystals to calculate the water concentration in the melt phase. If successful, this project will allow a much more detailed picture of the volatile evolution of magmas to be obtained.