Pre-eruptive conditions prior to and after magma mixing at Unzen volcano: constraints from high pressure experimental investigations

1991-1995年温泉喷发是由低温富斑晶英安岩岩浆和高温安山岩岩浆之间的混合事件(在许多喷发系统中观察到的)启动的，因此，了解喷发前的条件需要确定(两个端元岩浆)的预混合条件和后混合条件，并对混合和上升过程进行模拟。在温泉火山中，只有岩浆室中的后混合条件得到了很好的表征。拟议的项目应有助于对预混合岩浆，特别是高温端元(包括挥发分、熔体和斑晶成分)以及混合和岩浆上升过程提供新的约束。这些限制条件将通过高压-高温实验研究相关系和挥发分在硅酸盐熔体中的溶解度来获得。将使用来自火山穹隆(包括安山岩包体)和ICDP钻探的自然样品与实验结果进行比较，以了解混合(以及随后可能的脱气)对岩浆强迫的作用以及岩浆上升(动力学系统中的脱气、结晶)过程中的动力学过程的作用。

The 1991-1995 eruption of Unzen is initiated by a mixing event (as observed in many eruptive systems) between a low-temperature phenocryst-rich dacitic magma and a high temperature andesitic magma Thus, understanding pre-eruptive conditions requires to determine pre-mixing conditions (in the two end-member magmas) and post-mixing conditions, and to model the processes occurring during mixing and ascent. In Unzen volcano, only post-mixing conditions in the magma chamber are well-characterized. The proposed project should contribute to provide new constraints on the pre-mixing magmas, especially the high temperature end-member, (including volatile contents, melt and phenocryst compositions) and on processes occurring during mixing and magma ascent. These constraints will be obtained from high pressure - high temperature experimental investigations on phase relations and volatile solubilities in silicate melts. The comparison of natural samples from the volcanic dome (including andesitic enclaves) and from the ICDP-drilling with experimental results will be used to understand the role of mixing (and possible subsequent degassing) on magma forcing and the role of kinetic processes during magma ascent (degassing, crystallization in a dynamic system).