The influence of crystal size distributions on dynamic processes in magmatic systems

火山活动是由岩浆的流动驱动的。火山喷发是涌出式的还是爆发式的，往往只取决于岩浆流动特性的不同。因此，为了评估与火山爆发有关的灾害，尽可能准确地预测和模拟岩浆的输运特性，即了解岩浆流变学，是至关重要的。尽管在理解硅酸盐熔体以及两相混合物熔体-晶体的流变特性方面取得了重大进展，但在很大程度上仍然不清楚晶体粒度分布（CSD）以何种方式和在何种程度上影响岩浆的流变性。然而，在给定的浓度下，正是粒度分布强烈地影响着晶体的堆积排列和密度，从而也影响着整体岩浆的流变性。几乎所有可用的数值喷发和导管动力学模型，这并占晶体相的流变学的影响，是基于悬浮液的晶体相的尺寸变化。然而，在自然界中，晶体通常分布在一定尺寸范围内（即，岩浆是多分散的）。因此，悬浮液流变学对颗粒尺寸分布的依赖性必须得到很好的约束，以便对岩浆流动行为进行明智的预测。该项目的目的是：（a）实验和系统地调查（和定标）颗粒大小分布如何影响颗粒悬浮液的整体流变参数，（B）预测（使用新发现的实验定标）岩浆从火山管道上升和喷发时应遵循的流变路径。在一个新的和协同的方法，我们将结合联合收割机高压/高温岩石学实验与模拟实验的天然样品，以开发一套本构方程，将准确地描述天然含晶体岩浆的流变学。因此，该项目将由两部分组成：（一）多分散颗粒悬浮物的模拟实验，以研究CSD对流动特性的影响，并推导出基本的流变学定律，（二）岩石学实验，以重现沿着火山管道的压力/温度条件，并研究自然样品的相关CSD。这种组合方法的一个核心部分将是使用岩石学实验来约束晶体尺寸的演变作为火山管道中的压力和温度的函数，并使用这些所得的纹理作为模板，使我们能够合成匹配的模拟悬浮液用于进一步的流变测量。

Volcanic activity is driven by the flow of magma. Whether a volcano erupts effusively or explosively often only depends on differences in magma flow properties. For the assessment of hazards associated with a volcanic eruption, it is therefore of pivotal importance to predict and model the transport properties of magma as accurately as possible, i.e. to know the magma rheology. Despite significant progress in understanding the rheological properties of silicate melts, as well as those of the two-phase mixture melt-crystals, it remains largely unclear in what way and to what extent the crystal size distribution (CSD) affects the rheology of a magma. It is, however, precisely the size distribution which, at a given concentration, strongly affects the crystal packing arrangements and density, and hence also the bulk magma rheology. Virtually all available numerical eruption and conduit dynamics models, which do account for the rheological impact of the crystal phase, are based on suspensions with no size variation of the crystal phase. In nature, however, crystals are commonly distributed over a range of sizes (i.e., the magma is polydisperse). It is therefore imperative that the dependence of suspension rheology on the size distribution of the particles be well constrained, such that informed predictions of a magmas flow behaviour can be made. The aims of the project are: (a) to experimentally and systematically investigate (and scale), how particle size distributions affect the bulk rheological parameters of particle suspensions, and (b) to predict (using the newfound experimental scalings) the rheological paths a magma should follow when it is ascending and erupting from a volcanic conduit. In a novel and synergistic approach, we will combine HP/HT-petrology experiments on natural samples with analogue experiments, in order to develop a set of constitutive equations that will accurately describe the rheology of natural crystal-bearing magma. Accordingly, the project will be composed of two parts: (I) analogue experiments on polydisperse particle suspensions, in order to investigate the influence of CSDs on flow properties and to deduce fundamental rheological laws, and (II) petrology experiments to re-enact pressure/temperature conditions along a volcanic conduit and investigate the associated CSDs of natural samples. A central part of this combinational approach will be to use the petrology experiments to constrain the evolution of crystal sizes as a function of pressure and temperature in the volcanic conduit, and to use these resultant textures as templates allowing us to synthesize matching analogue suspensions to be used in further rheology measurements.