Carbon dioxide in ultrapotassic silicate melts: mechanisms and rates of magma degassing and their influence on the intensity and style of volcanic eruptions.

世界上一些最危险的活火山地区的特点是岩浆管道系统位于碳酸盐基底内：例如埃特纳火山、维苏威火山、Campi Flegrei火山和Colli Albani火山（意大利）；波波卡萨梅特和科利马（墨西哥）；默拉皮火山(印尼)。在接触变质反应过程中，岩浆-碳酸盐岩相互作用导致这些体系中大量存在二氧化碳。到目前为止，关于二氧化碳占主导地位的岩浆性质的实验数据缺失。确定CO2在岩浆上升动力学中的作用是理解和模拟以CO2为主的火山系统的脱气和破碎过程的先决条件，而且在深度处，相对不溶的CO2可能在水之外发挥重要作用。此外，这些信息对于明确定义不同挥发物在硅酸盐熔体中所起的作用至关重要。这项工作将对位于富含碳酸盐的地壳中的火山系统特征的超纯叠岩浆套件（如富辉岩和声母岩熔体）进行研究。在高压-高温装置上进行CO2- h2o溶解度实验和CO2扩散实验，研究近平衡条件下岩浆的性质。所获得的信息将有助于理解和描述深部（即岩浆房）的长期过程，如结晶、岩浆分异或围岩同化。此外，还将在能够进行可控减压的高压-高温装置上进行减压实验，以研究二氧化碳气泡成核和生长等中短期过程的动力学。相关系和脱气过程可能显著影响岩浆的流变性质，从而影响火山的破碎和喷发方式。获得的实验数据将与科利阿尔巴尼和维苏威火山自然样品的纹理模式和化学成分记录的信息进行比较。我们的实验数据将为高风险区的火山危险性评估提供有益的约束。

Some of the most dangerous active volcanic areas in the world are characterized by magmatic plumbing systems emplaced within carbonate substrata: e.g. Mt. Etna, Mt. Vesuvius, Campi Flegrei and Colli Albani (Italy); Popocatépetl and Colima (Mexico); Merapi (Indonesia). The magma-carbonate interaction during contact metamorphic reactions results in a significant presence of carbon dioxide in those systems. So far, experimental data on magma properties of CO2 dominated magmas are missing. Determining the role of CO2 in the dynamics of magma ascent is a pre-condition for understanding and modeling of degassing and fragmentation processes not only at CO2 dominated volcanic systems but also at depth, where the relatively insoluble CO2 may play an important role beside water. Furthermore, this information are crucial to unambiguously define the role played by different volatiles in the silicate melts.This work will be performed on ultrapotassic magma suites (e.g. foiditic and phonolitic melts), characteristic of volcanic systems emplaced in carbonate-rich crust. CO2-H2O solubility experiments and CO2 diffusion experiments will be carried out in high pressure-high temperature apparatus to investigate magma properties at near equilibrium conditions. The acquired information will be useful to understand and describe long-term processes at depth (i.e. in the magma chamber) such as crystallization, magma differentiation or wall rock assimilation. In addition, decompression experiments in high pressure-high temperature apparatus able to perform a controlled decompression will be performed to study the kinetics of short to intermediate term processes such as CO2 bubble nucleation and growth. Phase relation and degassing processes may significantly influence rheological magma properties and thus fragmentation and eruptive style of volcanoes. The obtained experimental data will be compared with the information recorded in the textural patterns and in the chemistry of the natural samples from Colli Albani and Mt. Vesuvius volcanoes.Our experimental data will provide useful constrain for volcanic hazard assessment at high risk volcanic areas.