Crystallization and melting experiments of a fluorine-rich leucogranite from the Xianghualing Pluton, South China, at 150 MPa and H 2O-saturated conditions

Abstract

Crystallization and melting experiments were conducted with a fluorine-rich granite from the Xianghualing Pluton, South China, in order to determine its crystallization sequence and melt fractionation trends at 150 MPa and H 2O-saturated conditions, which are close to the crystallization conditions of this pluton. The experimental results showed that quartz is the liquidus phase and is sequentially followed by K-rich alkali feldspar, zinnwaldite, albite, and topaz. There are obvious evolutionary trends in the compositions of alkali feldspar and residual melt with decreasing temperature from liquidus to 600 °C. The Or (KAlSi 3O 8) content in alkali feldspar increases and the contents of Ab (NaAlSi 3O 8) and An (CaAl 2Si 2O 8) decrease. The most apparent fractionation trends in residual melt compositions are decreases in the SiO 2 and K 2O contents and Si/Al ratio, and increases in the contents of Na 2O, F, Al 2O 3, CaO, and the ratios of A/NKC and Na/K. These experimental results indicate that a low-silica and sodic granitic melt could be derived from a relatively high-silica and potassic F-rich leucogranitic magma via fractional crystallization. They also shed light on the fractional crystallization and vertical zoning of the Xianghualing Pluton and other similar high-level, F-rich leucogranite plutons.