Synthetic fluid inclusions XIV: Coexisting silicate melt and aqueous fluid inclusions in the Haplogranite-H₂O-NaCl-KCl system

Coeval silicate melt and aqueous synthetic fluid inclusions were formed at 800°C and 2000 bars in the quartz-saturated haplogranite-H₂O-NaCl-KCl system. The equilibrium assemblage consisted of Ab(19.2)Or(31.1)Qtz(49.1) melt, quartz, and an aqueous solution with a composition of 7.4 wt % NaCl + 5.9 wt % KCl. The melt contained 0.18 wt % Cl and ~5.5 wt % H₂O. The calculated partition coefficient of chloride between the melt and aqueous fluid (D(Cl)(m/aq) = C(Cl)^m/C(Cl)(aq) is 0.021. The calculated distribution coefficient of Na and K between the melt and the acqueous phase D(Na/K)(m/aq) = (C(Na)(ma)/C(K)(aq))) is 0.40. Homogenization temperatures of synthetic silicate melt inclusions obtained by heating in 10.0°C/day increments in a tube furnace agreed with known formation temperatures, with no size dependence. When measured in a high-temperature heating stage, a heating rate of 1°C/min produced homogenization temperatures that were about 10°C lower than those obtained from the same inclusions using a heating rate of 3°C/min, although both heating rates produced homogenization temperatures above the formation temperature. A positive correlation between inclusion size and T(h) was observed for both heating rates. Results confirm that microthermometric data from coeval silicate melt and aqueous fluid inclusions can be used to accurately predict P-T formation conditions if data from the smallest melt inclusions are used, or if the melt inclusions are homogenized using a slow heating rate (<1°C/min).