Abstract

New experimental data from synthetic fluid-inclusion studies in the system K2O-CO2-SiO2-H2O (KCSH) show that a potassic, silica-rich (≈ 90 wt% SiO2) fluid can coexist immiscibly with a supercritical, alkaline, aqueo-carbonic fluid and quartz from temperatures as low as 300 °C to more than 750 °C at relatively low geologic pressures (<200 MPa). This type of fluid phase may form in a range of geologic environments, including carbonatite complexes, alkaline subvolcanic-plutonic systems, and subduction zones. With a probable polymerized (silica-rich, melt-like) structure, such SiO2-rich fluids, if they form in the lithosphere, are likely to be important in the mobilization and transport of silica and large ion lithophile elements (e.g., K, Cs, Ba) and metals of economic significance (e.g., Au, Ag, U).

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