Hydrous alkali-silicate liquids at the magmatic-hydrothermal transition

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This proposal focuses on alkali-silicate liquids with the highest solubility of H2O and the lowest solidus temperatures. The nature of these liquids is contentious. They are considered either as melts, or concentrated aqueous solutions, or colloidal gels. However, they are able to crystallise common rock-forming silicates, such as feldspars and quartz, and thus can be regarded as plausible magmatic liquids. Natural alkali silicate liquids are likely to play an important role at the final stages of magma crystallisation in felsic intrusions, during anatectic melting of the crust and they may also form in subduction zone magmatism. The project includes comprehensive experimental studies in synthetic systems, and involves experimental and analytical methods (hydrothermal diamond anvil cells, in situ Raman spectroscopy, laser ablation ICP-MS), some of which, such as ultrasonic spectroscopy, were never applied, as far as we know, to water-rich alkali-silicate liquids before. By using new tools, we expect to resolve the controversy regarding the nature of the amorphous silicate phases and particularly examine their role in geologic systems at the magmatic-hydrothermal transition. The project aims at a major breakthrough in understanding pegmatite formation from alkali silicate liquids and has broader implications for fluid-induced melting in continental crust and lithospheric mantle. Amorphous silicate materials (liquid, glassy or colloidal) with large contents of water may shed new light on solubility mechanisms of volatiles in silicate melts and are also of great interest to material science.