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

晶体尺寸分布对岩浆系统动态过程的影响

基本信息

批准号：
253685848
负责人：
Professor Dr. Jonathan Castro
金额：
--
依托单位：
Institut für Geowissenschaften
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2014
资助国家：
德国
起止时间：
2013-12-31 至 2017-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/253685848?language=en
关键词：
influence crystal size distributions dynamic

项目摘要

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.

火山活动是由岩浆流驱动的。一座火山是喷涌式喷发还是爆发性喷发，通常只取决于岩浆流动性质的不同。因此，尽可能准确地预测和模拟岩浆的运移性质，即了解岩浆的流变学，对于火山喷发危险性的评估具有至关重要的意义。尽管在了解硅酸盐熔体以及两相混合熔体晶体的流变性能方面取得了重大进展，但晶体尺寸分布（CSD）以何种方式和在多大程度上影响岩浆的流变性能仍不清楚。然而，在一定的浓度下，恰恰是大小的分布强烈地影响着晶体的排列和密度，从而也影响着岩浆的整体流变性。几乎所有可用的数值喷发和导管动力学模型都是基于悬浮液，没有晶体相的大小变化，这些模型确实考虑了晶体相的流变影响。然而，在自然界中，晶体通常分布在一定的大小范围内（即，岩浆是多分散的）。因此，悬浮液流变性对颗粒大小分布的依赖性必须得到很好的约束，这样才能对岩浆流动行为做出明智的预测。该项目的目的是：(a)实验和系统地调查（和缩放），粒度分布如何影响颗粒悬浮物的总体流变参数，以及(b)预测（使用新发现的实验缩放）岩浆从火山管道上升和喷发时应该遵循的流变路径。我们将采用一种新颖的协同方法，将天然样品的高温高压岩石学实验与模拟实验相结合，以建立一套准确描述天然含晶岩浆流变学的本构方程。因此，该项目将由两部分组成：(I)多分散颗粒悬浮液的模拟实验，以研究CSDs对流动特性的影响并推断基本流变规律；（II）岩石学实验，以重新制定火山导管的压力/温度条件，并研究自然样品的相关CSDs。这种组合方法的核心部分将是使用岩石学实验来约束火山导管中晶体尺寸随压力和温度的变化，并使用这些合成的纹理作为模板，使我们能够合成匹配的模拟悬浮液，用于进一步的流变学测量。