CO2 diffusion and degassing in volcanic melts

火山的喷发行为受到岩浆挥发物（主要是H2O和CO2）的严重影响。在富含挥发性的岩浆上升过程中，由于压力的降低，可能发生气泡成核和气泡生长。最后，喷发的岩浆可能会碎裂，导致爆炸性和危险的火山爆发。本研究项目的目的是有助于理解富CO2硅酸盐熔体的脱气机制。为此，将研究硅酸盐熔体中CO2的流动性（扩散）以及富CO2熔体的脱气。以前的研究集中在扩散和脱气的H2O。因此，有必要对CO2的实验数据，这是第二个最丰富的挥发性岩浆熔体内。CO2扩散将通过扩散偶实验研究在高压和高温以上的液相线使用内部加热的压力容器（IHPV）。将用于扩散实验的熔体成分基于Stromboli（玄武岩）、Popocatépetl（英安岩）和Vesuvius（响岩）的天然火山熔体。由于H2O对CO2扩散有很强的影响，并且由于它经常存在于天然熔体中，因此将使用熔体中不同的H2O浓度进行实验。因此，将系统地研究不同参数（熔体组成、H2O浓度、温度）的个体影响。富CO2熔体的脱气行为将通过减压实验使用IHPV模拟不同的上升速率的岩浆上升进行研究。为了研究CO2的脱气，将使用名义上不含H2O的熔体进行实验。减压实验将使用以前在扩散实验中使用的相同玄武质和响岩熔体进行。实验将特别揭示气泡成核和气泡生长的过程。将评估减压速率和熔体组成的影响。关于扩散和脱气的信息对于模拟岩浆上升和根据火山气体排放预测火山爆发十分重要。所获得的实验数据也将允许与其他挥发物（主要是H2O）的扩散和脱气行为进行比较，以便更好地了解天然火山系统。

The eruptive behaviour of a volcano is heavily influenced by the volatiles of the magma (mainly H2O and CO2). During the ascent of a volatile rich magma, bubble nucleation and bubble growth can occur due to the decrease in pressure. Finally, an erupting magma can be fragmented, which results in explosive and dangerous volcanic eruptions. The aim of this research project is to contribute to the understanding of the degassing mechanisms of CO2-rich silicate melts. For that purpose, the mobility of CO2 in silicate melts (diffusion) as well as the degassing of CO2-rich melts will be investigated. Previous studies focussed on diffusion and degassing of H2O. Consequently, there is a need for experimental data on CO2, which represents the second most abundant volatile within magmatic melts. CO2 diffusion will be investigated via diffusion couple experiments at high pressure and high temperatures above the liquidus using an internally heated pressure vessel (IHPV). The melt compositions that will be used for the diffusion experiments are based on natural volcanic melts from Stromboli (basaltic), Popocatépetl (dacitic) and Vesuvius (phonolitic). Since H2O has a strong influence on CO2 diffusion and because it is often present in natural melts, the experiments will be performed using different H2O concentrations in the melts. As a result, the individual influences of different parameters (melt composition, H2O concentration, temperature) will be investigated systematically. The degassing behaviour of CO2-rich melts will be investigated via decompression experiments using the IHPV by simulating a magma ascent with different ascent rates. In order to investigate the degassing of CO2, the experiments will be performed using nominally H2O-free melts. Decompression experiments will be performed using the same basaltic and phonolitic melts that were previously used in diffusion experiments. The experiments will especially shed light on processes of bubble nucleation and bubble growth. The effects of decompression rate and melt composition will be evaluated. Information on diffusion and degassing is important for modelling magma ascent and predicting volcanic eruptions based on volcanic gas emissions. The obtained experimental data will also allow a comparison with the diffusion and degassing behaviour of other volatiles (mainly H2O) for a better understanding of natural volcanic systems.