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跃火山地区的特点是岩浆管道系统布设在碳酸盐基岩中：例如，山体。埃特纳，Mt.Vesuvius、Campi Flegrei和Colli阿尔巴i(意大利)；Popocatépetl和Colima(墨西哥)；Merapi(印度尼西亚)。接触变质反应过程中的岩浆-碳酸盐相互作用导致这些体系中大量存在二氧化碳。到目前为止，还没有关于二氧化碳占主导地位的岩浆性质的实验数据。确定CO2在岩浆上升动力学中的作用是了解和模拟脱气和碎裂过程的先决条件，不仅在以CO2为主的火山系统，而且在深层，相对不溶的CO2可能在水之外发挥重要作用。此外，这些信息对于明确确定不同挥发物在硅酸盐熔体中所起的作用至关重要。这项工作将在超钾质岩浆套(例如，橄榄岩和声橄榄岩熔体)上进行，这是富含碳酸盐的地壳中火山系统的特征。CO2-H2O溶解实验和CO2扩散实验将在高压高温装置上进行，以研究近平衡条件下的岩浆性质。所获得的信息将有助于理解和描述深部(即岩浆室中)的长期过程，如结晶、岩浆分异或围岩同化。此外，还将在能够进行受控减压的高压高温装置上进行减压实验，以研究CO2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流变性岩浆的性质，从而影响火山的碎裂和喷发方式。所获得的实验数据将与科利、阿尔巴尼和芒特的天然样品的纹理图案和化学中记录的信息进行比较。我们的实验数据将为高风险火山区的火山危险性评估提供有用的约束。

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.