Determining Large-Scale Permeability of Magma From its Bubble and Crystal Microstructure - A Multiphase Percolation Theory Approach

大规模的岩浆渗透性和相关的挥发性脱气率尚不清楚，尽管气体通过气泡网络的流动是理解岩浆性质和过程的核心。其中包括气泡和晶体含量以及相关的岩浆流变学、火山气体的排放、管道塞的加压和破坏、岩浆破碎和随后的膨胀、喷发动力学的转变以及熔岩流就位特征等。本研究旨在利用小规模喷发产物的微观结构分析作为基于渗流理论的计算机模型的输入参数，在数值上确定岩浆对挥发物的渗透率。目标是重建与问题过程相关的大规模平均喷发前微观结构（例如，喷发动力学的管道尺度）。具体而言，本文主要解决了以下三个问题：1)在何种（气泡和晶体）微观结构条件下，岩浆和熔岩中可能存在气泡网络；2)气泡网络的宏观渗透率如何；3)这种渗透途径如何影响挥发性脱气速率和岩浆/熔岩流变学（与渗透率发展的反馈）。多相渗流计算机代码是本提案和本研究结果的一部分，也可用于描述泡状颗粒悬浮液的行为，通常在许多物理科学和工程中遇到。

Large-scale magma permeabilities and associated volatile degassing rates are poorly understood even though the flow of gases through bubble networks is central to understanding a wide range of magmatic properties and processes. These include bubble and crystal content and related magma rheology, emissions of volcanic gases, pressurization and destruction of conduit plugs, magma fragmentation and subsequent expansion, and transitions in eruption dynamics as well as lava flow emplacement characteristics among others. This proposal aims at numerically determining the permeability of magmas for volatiles using microstructure analyses of small-scale eruption products as input parameters to percolation-theory-based computer models. The goal is to reconstruct the average pre-eruptive microstructure over a large scale that is relevant to the process in question (e.g., conduit scale for eruption dynamics). Specifically, this proposal addresses the following three main questions: 1) under which (bubble and crystal) microstructure conditions are bubble networks expected to exist in magmas and lavas; 2) what are the bubble networks' macroscopic permeabilities; and 3) how do such permeable pathways affect volatile degassing rates and magma/lava rheologies (with feedback to permeability development). The multiphase percolation computer code that is part of this proposal and results from this study may also be used to describe the behavior of vesicular particle suspensions in general as encountered in numerous physical sciences and in engineering.