Kinetics and the extent of immiscibility in basaltic liquids

淬火硅酸盐玻璃中亚微米液-液分离的解释是实验岩石学和材料科学中一个长期存在的问题。纳米尺度的非均质性通常被解释为亚液相、亚稳态不混相的产物。然而，当相分离和液滴生长受到缓慢动力学的阻碍时，这种非均质性也可能由超液相、热力学稳定的液体不混相形成。来自天然熔体包裹体的新证据、以前的实验工作和我们自己最近的实验表明，常见的天然玄武岩-安山岩液体的结晶路径非常接近液体不混溶的组成区域。然而，该体系表现出很强的亚稳结晶倾向，并且由于动力学障碍的存在，液体不混相的实验重现也很困难。在稳定混相间隙附近的硅酸盐熔体可能形成持久的胶状乳剂，这使得区分稳定解混和亚稳定解混变得非常复杂。本研究计划解决了以前在具有地质重要性的铝硅酸盐熔体中不混溶性研究中遇到的实验问题。稳定和亚稳不混溶性之间的区别是这个项目的中心主题。我们建议结合高温离心、粘度测量、布里频光谱、小角x射线（SAXS）和中子（SANS）散射等原位实验技术，研究超液相硅酸盐乳状液的形成和稳定性，并监测熔体分解。相分离的发展也将通过电子探针分析和淬火玻璃中液滴尺寸分布的统计分析来记录。我们计划测量液-液界面能和矿-液润湿角，这对乳剂的粗化和晶体糊状中非混相液体的流动性至关重要。实验测量的物理性质将用于定量解释火山玻璃、熔融包裹体和完全结晶的深成岩结构中记录的自然不混溶性。这将与一个由火成岩岩石学家和层状辉长岩侵入岩专家组成的国际团队合作完成。到目前为止，实验研究与天然火成岩的详细文件的结合非常富有成效，我们计划继续这种富有成效的合作。将特别注意在缓慢冷却的岩浆房中解混和结晶之间的关系。液体不混溶性，即使没有发展到纳米级乳剂之外，也有望对火山和深部环境中的岩浆动力学和分异产生深远的影响。

Interpretation of sub-micron liquid-liquid phase separation in quenched silicate glasses is a longstanding problem of experimental petrology and material science. Nanoscale heterogeneity is usually interpreted as a product of sub-liquidus, metastable immiscibility. However, such heterogeneity may also form by super-liquidus, thermodynamically stable liquid immiscibility when phase separation and droplet growth are hampered by sluggish kinetics. New evidence from natural melt inclusions, previous experimental work and our own recent experiments imply that crystallization paths of common natural basaltic-andesitic liquids closely approach the compositional regions of liquid immiscibility. However, the systems show strong tendency to metastable crystallization, and experimental reproduction of liquid immiscibility is very difficult also because of kinetic barriers. Silicate melts in the vicinity of stable miscibility gaps may form long-lasting colloidal emulsions, which greatly complicate the distinction between stable and metastable unmixing. This research proposal addresses experimental problems that have been encountered by previous studies of immiscibility in aluminosilicate melts of geological importance. The distinction between stable and metastable immiscibility is the central theme of this project. We propose to study the formation and stability of sup er-liquidus silicate emulsions and monitor melt unmixing by a combination of in situ experimental techniques including high temperature centrifugation, viscosity measurements, Brillouin spectroscopy, small angle X-ray (SAXS) and neutron (SANS) scattering. The development of phase separation will be also documented by electron microprobe analyses and the statistical analysis of droplet size distribution in quenched glasses. We are planning to measure liquid-liquid interfacial energies and mineral-liquid wetting angles, which are crucial for the coarsening of emulsions and the mobility of immiscibJe liquids in a crystal mush. Experimentally measured physical properties will be used for quantitative interpretation of natural immiscibility recorded in volcanic glasses, melt inclusions and textures of fully crystallized plutonic rocks. This will be done in collaboration with an international team of igneous petrologists and experts on layered gabbroic intrusions, The combination of experimental studies with detailed documentation of natural igneous rocks has been very productive so far, and we are planning to continue this fruitful collaboration. Special attention will be given to relationships between unmixing and crystallization in slowly cooling magma chambers. Liquid immiscibility, even if it does not develop beyond the nanoscale emulsions, is expected to have profound effects on magma dynamics and differentiation in volcanic and plutonic environments.