Kinetics and the extent of immiscibility in basaltic liquids

淬火硅酸盐玻璃中亚微米液-液相分离现象的解释是实验岩石学和材料科学的一个长期难题。纳米尺度的不均匀性通常被解释为亚液相线、亚稳态不均匀性的产物。然而，当相分离和液滴生长受到缓慢动力学的阻碍时，这种不均匀性也可以通过超液相线、热稳定的液体不可渗透性形成。天然熔体包裹体，以前的实验工作和我们自己最近的实验的新证据表明，常见的天然玄武安山岩液体的结晶路径密切接近液体不可渗透的成分区域。然而，该系统显示出强烈的倾向，亚稳结晶，和实验再现的液体不溶性也是非常困难的，因为动力学障碍。硅酸盐熔体在稳定的溶解间隙附近可能形成持久的胶体乳液，这大大复杂了稳定和亚稳不混合之间的区别。这项研究建议解决了以前的研究中遇到的实验问题，在铝硅酸盐熔体的地质重要性的不可渗透性。稳定和亚稳定不可分割性之间的区别是这个项目的中心主题。我们建议研究超液相线硅酸盐乳液的形成和稳定性，并通过原位实验技术，包括高温离心，粘度测量，布里渊光谱，小角X射线（SAXS）和中子（SANS）散射相结合，监测熔体不混合。相分离的发展也将记录在淬火玻璃中的电子探针分析和液滴尺寸分布的统计分析。我们正计划测量液-液界面能和矿物-液体润湿角，这对乳液的粗化和晶体糊状物中不可渗透液体的流动性至关重要。实验测得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的结构中记录的自然不渗透性。这将与一个由火成岩岩石学家和层状辉长岩侵入体专家组成的国际团队合作完成，迄今为止，实验研究与天然火成岩详细记录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不混合和结晶之间的关系。液体的不可渗透性，即使它没有发展超出纳米级的乳液，预计将有深远的影响，岩浆动力学和火山和深成环境中的分化。

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.