Pursuing the Nucleus: Experimental, Theoretical, and Analytical Investigations of Bubble and Crystal Formation in Magma

岩浆通常由三种主要成分组成，熔体，一种或几种类型的矿物，以及气泡形式的气相。矿物（或晶体）和汽相（气泡）的形成和生长对它们的寄主岩浆的行为产生重大影响，因为它们改变了岩浆？的物理性质（例如，粘度/流动性、体积）并影响其热力学状态（例如，相之间的热量和质量分布），最终控制将发生的喷发类型（例如，喷发与爆炸）。从熔体中形成晶体和气泡是通过一个自发的过程发生的。成核？在此期间晶体和蒸汽形成组分聚集到临界尺寸。然后，这些晶核通过向新形成的熔体-晶体或熔体-气泡界面进一步添加组分而生长。了解岩浆中的成核过程是至关重要的，因为核的初始数量控制着晶体或气泡的最终分布。该提案旨在通过实验和分析方法更好地了解晶体和气泡核的形成。这些结果可能会影响我们对成核理论的理解，实验数据可以在预测物理和数值岩浆上升和喷发models.The成核的能量学和动力学越来越好地理解玻璃陶瓷，一类工程材料，其中玻璃主机的高人口密度的纳米级晶体。工业玻璃陶瓷的发展和表征刺激了玻璃的纳米分析和光谱研究的技术发展，为研究天然铝硅酸盐熔体中的成核提供了前所未有的机会。在其基本形式中，经典成核理论可用于模拟自然熔体的实验成核数据，但只有当有关界面能（晶体）和表面张力（气泡）的关键假设放松时。缺乏对这些能量项的坚定理解，这些能量项在纳米尺度上起作用，因此难以用常规成像技术实现，这尤其令人不安，因为理论规定它们对成核速率的影响是深远的。另一个复杂性是，虽然岩浆中的成核似乎发生均匀的晶体，因此只涉及两个阶段，气泡的成核可能会发生更典型的非均相过程中，涉及三个阶段之间的能量关系。该项目建议（1）实验研究中间（安山岩）和流纹岩（流纹岩）熔体中的晶体和气泡成核，（2）在这些天然岩浆的背景下重新审视经典成核理论，（3）探索空间前沿（即，纳米级）的初始结晶通过目前可用的尖端分析仪器，和（4）执行一个新的动态结晶实验，以评估岩浆流和剪切晶体成核的影响。所提出的努力，以了解气泡和晶体成核动力学hasfar-reaching物理火山学，这是越来越多地关注岩浆上升过程中发生的相变领域的影响。

Magmas are generally composed of three main components, a melt, one or several types of minerals, and a vapor phase in the form of bubbles. The formation and growth of minerals (or crystals) and of the vapor phase (bubbles) exerts a major influence on the behavior of their host magmas because they modify the magma?s physical properties (e.g., viscosity/fluidity, volume) and influence its thermodynamic state (e.g. heat and mass distribution among phases), ultimately controlling what type of eruption (e.g. effusive vs. explosive) will occur. The formation of crystals and bubbles from the melt occurs via a process of spontaneous ?nucleation?, during which the crystal and vapor-forming components aggregate to a critical size. These nuclei then grow by further addition of components to the newly formed melt-crystal or melt-bubble interface. It is critical to understand the nucleation process in magmas because the initial number of nuclei controls the final distribution of crystals or bubbles. This proposal aims to better understand the formation of crystal and bubble nuclei via experimental and analytical approaches. The results could influence our understanding of nucleation theory, and experimental data could be implemented in predictive physical and numerical magma ascent and eruption models.The energetics and kinetics of nucleation are increasingly well understood for glass ceramics, a class of engineered materials in which a glass hosts a high population density of nm-scale crystals. The development and characterization of industrial glass ceramics has stimulated technological developments in nanoanalysis and spectroscopic investigation of glasses, providing unprecedented opportunities for studying nucleation in naturally-occurring aluminosilicate melts. In its fundamental form, the Classical Nucleation Theory may be used to model experimental nucleation data for natural melts, but only if key assumptions concerning interfacial energy (for crystals) and surface tension (bubbles) are relaxed. Lack of firm understanding of these energy terms, operative at the nanometer scale and therefore elusive to conventional imaging techniques, is especially troubling because the theory stipulates that their influence over nucleation rate is profound. An additional complexity is that while nucleation in magma appears to occur homogeneously for crystals, thus involving just two phases, nucleation of bubbles may occur more typically by a heterogeneous process, involving energetic relationships among three phases. This project proposes to (1) experimentally investigate crystal and bubble nucleation in an intermediate (andesitic) and a silicic (rhyolite) melt, (2) revisit classical nucleation theory in the context of these natural magmas, (3) explore the spatial frontier (i.e., nanoscale) of incipient crystallization via cuttingedge analytical instruments presently available, and (4) perform a novel dynamic crystallization experiment to evaluate the influence of magma flow and shearing on crystal nucleation. The proposed effort to understand bubble and crystal nucleation kinetics hasfar-reaching implications for the field of physical volcanology, which is increasingly concerned with phase transformations occurring during magma ascent.