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

追寻原子核：岩浆中气泡和晶体形成的实验、理论和分析研究

• 批准号: 1321890
• 负责人: Thomas Shea
• 金额: $ 26.62万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-01 至 2017-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1321890&HistoricalAwards=false
• 关键词: Pursuing; Nucleus; Experimental; Theoretical; Analytical

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.

岩浆一般由三种主要成分组成：熔体、一种或几种矿物质以及气泡形式的气相。矿物（或晶体）和气相（气泡）的形成和生长对其宿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（例如各相之间的热量和质量分布），最终控制将发生哪种类型的喷发（例如喷发与爆炸）。熔体中晶体和气泡的形成是通过自发“成核”过程发生的，在此过程中晶体和蒸气形成组分聚集到临界尺寸。然后，通过向新形成的熔体-晶体或熔体-气泡界面进一步添加成分，这些核会生长。了解岩浆中的成核过程至关重要，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，并且实验数据可以在预测性物理和数值岩浆上升和喷发模型中得到应用。玻璃陶瓷的成核能量和动力学越来越被人们所理解，玻璃陶瓷是一类工程材料，其中玻璃中含有高密度的纳米级晶体。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。就其基本形式而言，经典成核理论可用于模拟自然熔体的实验成核数据，但前提是有关界面能（对于晶体）和表面张力（气泡）的关键假设得到放松。对这些能量术语缺乏深入的理解尤其令人不安，因为这些能量术语在纳米尺度上运行，因此传统成像技术难以捉摸，因为该理论规定它们对成核率的影响是深远的。另一个复杂性是，虽然岩浆中的成核对于晶体来说似乎是均匀发生的，因此仅涉及两相，但气泡的成核可能更典型地通过异质过程发生，涉及三相之间的能量关系。该项目建议（1）通过实验研究中间体（安山岩）和硅质（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）通过现有的尖端分析仪器探索初期结晶的空间前沿（即纳米尺度），以及（4）进行新颖的动态结晶 实验评估岩浆流动和剪切对晶体成核的影响。所提出的理解气泡和晶体成核动力学的努力对物理火山学领域具有深远的影响，该领域越来越关注岩浆上升过程中发生的相变。

项目成果

Accuracy of timescales retrieved from diffusion modeling in olivine: A 3D perspective

• DOI: 10.2138/am-2015-5163
• 发表时间: 2015-10
• 期刊: American Mineralogist
• 影响因子: 3.1
• 作者: T. Shea;F. Costa;D. Krimer;J. Hammer

Lithium diffusion in olivine records magmatic priming of explosive basaltic eruptions

• DOI: 10.1016/j.epsl.2018.08.002
• 发表时间: 2018-10
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: K. Lynn;T. Shea;Michael O. Garcia;F. Costa;M. Norman

Cracking the olivine zoning code: Distinguishing between crystal growth and diffusion

破解橄榄石分区密码：区分晶体生长和扩散

• DOI: 10.1130/g37082.1
• 发表时间: 2015
• 期刊: Geology
• 影响因子: 5.8
• 作者: Shea, Thomas;Lynn, Kendra J.;Garcia, Michael O.
• 通讯作者: Garcia, Michael O.

Timescales of mixing and storage for Keanakāko‘i Tephra magmas (1500–1820 C.E.), Kīlauea Volcano, Hawai‘i

夏威夷 Kälauea 火山 Keanakäkoäi Tephra 岩浆（公元 1500 年至 1820 年）混合和储存的时间尺度

• DOI: 10.1007/s00410-017-1395-4
• 发表时间: 2017
• 期刊: Contributions to Mineralogy and Petrology
• 影响因子: 3.5
• 作者: Lynn, Kendra J.;Garcia, Michael O.;Shea, Thomas;Costa, Fidel;Swanson, Donald A.
• 通讯作者: Swanson, Donald A.

Bubble nucleation in magmas: A dominantly heterogeneous process?

• DOI: 10.1016/j.jvolgeores.2017.06.025
• 发表时间: 2017-09
• 期刊: Journal of Volcanology and Geothermal Research
• 影响因子: 2.9
• 作者: T. Shea