RUI: Crystallization of Hydrous Silicic Melts in Nature and Experiments

智力价值：新的证据表明，侵入上地壳的无晶体花岗岩熔体薄片可以在几周内冷却到亚液线温度。由于含水硅熔体成核速度较慢，这种强烈的过冷度可能控制着它们的结晶和地球化学演化路径。研究表明，溶解水和其他助熔剂组分(如Li、B)降低了熔体粘度和玻璃化转变温度，从而使硅酸盐液体在异常低温下保持不变。地质测温、结构和成分数据揭示了这种熔体结晶历史的重要方面，但还需要更多的实验约束来破译过冷的结构和地球化学后果。这项为期三年的计划的目标是通过现场观察和实验观察，确定硅质侵入岩的结构、成分和结晶历史之间的联系。勘察实验证据表明，在300兆帕的压力下，温度低至400℃时，存在含水的含锂和含硼的单花岗岩熔体。为这些成分测量的玻璃化转变温度(250-300°C)支持实验观察。这些过冷液体的成核和结晶至少被亚稳地推迟了30天。当结晶最终发生时，根据过冷度和溶水量的不同，产生了独特的结构，这些结构专属于伟晶岩(球晶、图形、骨架、单向等)、辉长岩(细粒、等长)和流纹岩(斑状、真面体)。高的晶体生长速度可能导致在凝固前沿前方形成化学和同位素边界层。成核和生长速度与较大的增量建造的深成岩中的小侵入体或薄片的冷却时间表是一致的。这项研究的一个基于现场的组成部分将限制岩浆片向内结晶期间的就位温度、温度梯度、冷却速度、过冷和流体饱和度。拟议的研究包括流体和熔体包裹体研究、传导冷却模拟以及对两个研究区样品的矿物和同位素分析。重点将放在冷却边缘和分层的、单向的和球状的纹理上，这些纹理被解释为快速结晶的后果。将努力查明和量化化学和同位素边界层的存在。一个实验组件将解决合成熔体组合物的结晶问题，寻求在300兆帕以及不同程度的过冷和冷却速度下量化熔剂花岗岩熔体的结晶动力学。我们将扩大我们对B-Li-H2O-单长花岗岩系统的成核和晶体生长速率的研究，重点是水对结晶动力学的控制作用，并最终控制岩浆结构。为了对合成熔体进行完整的表征，将在大学测量粘度和玻璃化转变温度。与惠廷顿博士合作。还将在实验装药中研究快速、不平衡结晶过程中凝固前沿的化学扩散。将评估扩散驱动的边界层及其对矿物和结构分带、熔体包裹体成分和地球化学分馏的潜在影响。在更广泛的岩石学社区内的影响将是显著的，因为基于综合野外实验观察、自然中低温熔体的鉴定以及快速结晶产生的扩散相关的同位素分馏对结构的解释将提高我们对过冷熔体的理解，无论其组成如何。广泛影响：为了在大学和更大的社区内传播我们的结果，将开发一个关于岩浆结构的起源和意义的教育展览，作为中央密歇根大学(CMU)文化和自然历史博物馆的一部分，并将提供关于结晶活动的公开演示。这个RUI项目将使CMU本科生项目受益，因为它将允许PI培训和指导参与研究各个阶段的几名本科生。CMU拥有资源和非常坚定的本科生研究承诺。CMU本科生将有机会前往德国波茨坦大学著名的研究实验室工作和旅行。密歇根大学和密歇根大学。密苏里州。

Intellectual Merit: New evidence suggests that thin sheets of crystal-free granitic melts intruded in the upper crust can cool to subliquidus temperatures within weeks. Because hydrous silicic melts are sluggish to nucleate, such strong undercooling may govern their crystallization and geochemical evolution paths. It is proposed that dissolved water and other fluxing components (e.g., Li, B) lower melt viscosity and the glass-transition temperature, thus allowing the silicate liquids to persist at unusually low temperatures. Geothermometric, textural and compositional data have revealed important aspects of the crystallization history of such melts, but more experimental constraints are needed to decipher the textural and geochemical consequences of undercooling. The goal of this three-year proposal is to identify links between texture, composition, and crystallization history of silicic intrusive rocks by using field-based and experimental observations. Reconnaissance experimental evidence has demonstrated the existence of hydrous Li- and B-bearing haplogranitic melts at temperatures as low as 400°C at a pressure of 300 MPa. Glass transition temperatures (ranging between 250-300°C) measured for these compositions support the experimental observations. Nucleation and crystallization of these undercooled liquids was metastably delayed for at least 30 days. When crystallization finally took place, distinctive textures resulted depending on degree of undercooling and amount of dissolved water, that are specific to pegmatites (spherulitic, graphic, skeletal, unidirectional, etc.), aplites (fine grained, equigranular), and rhyolites (porphyritic, euhedral). High crystal growth rates can lead to chemical and isotopic boundary layers ahead of the solidification front. Nucleation and growth rates are consistent with cooling timelines of small intrusions or sheets within larger incrementally built plutons. A field-based component of the study will constrain emplacement temperatures, temperature gradients, cooling rates, undercooling, and fluid saturation during inward crystallization of magma sheets. Proposed research includes fluid and melt inclusion studies, conductive-cooling simulations, and mineral and isotopic analyses on samples from two study areas. Focus will be on chilled margins and layered, unidirectional, and spherulitic textures interpreted as consequences of rapid crystallization. Attempts will be made to identify and quantify the existence of chemical and isotopic boundary layers. An experimental component will address crystallization of synthetic melt compositions seeking to quantify the kinetics of crystallization of fluxed granitic melt at 300 MPa and various degrees of undercooling and cooling rates. We will expand our study on nucleation and crystal growth rates in the B-Li-H2O-haplogranite system with emphasis on the role of water on controlling the crystallization kinetics and, ultimately, the magmatic texture. For a complete characterization of the synthetic melts, the viscosities and glass transition temperatures will be measured at the Univ. of Missouri, in collaboration with Dr. Whittington. Chemical diffusion ahead of the solidification front during rapid, disequilibrium crystallization will also be investigated in experimental charges. Diffusion-driven boundary layers and their potential impact on mineral and textural zoning, melt inclusion compositions, and geochemical fractionation will be evaluated. The impact within the broader petrologic community will be significant, because the interpretation of texture based on integrated field-experiment observations, identification of low temperature melts in nature, and diffusion-related isotopic fractionation produced by rapid crystallization will improve our understanding of undercooled melts, regardless of their composition.Broader Impact: To disseminate our results within the University and larger community, an educational exhibit on the origin and significance of magmatic texture will be developed as part of the Museum of Cultural and Natural History at Central Michigan University (CMU) and public presentations will be given with hands on crystallization activities. This RUI project will benefit the CMU undergraduate program in that it will allow the PI to train and mentor several undergraduates involved at all stages of research. Resources and a very strong commitment to undergraduate research exist at CMU. Undergraduate CMU students will have the opportunity to travel and work at prestigious research laboratories at GFZ-Potsdam, Germany, Univ. of Michigan, and Univ. of Missouri.