VOLATILES IN THE EARTHS MANTLE: I. SYNTHESIS OF CHO FLUIDS AT 1273 K AND 2.4 GPA

Abstract

We have synthesized graphite-saturated CHO fluids at 1273K and 2.4 GPa over 7.5 orders of magnitude in fO2. Bulk H/O of the fluid ranges from 1.78 (oxidized fluids in the H2O-CO2 stability field) to 1330 (highly reduced fluids at the Si-SiC buffer). The maximum H2O content at 1273K and 2.4 GPa at the water maximum (H/O = 2) is 95 +/- 1 mol%. Molar H2 is <0.05% in the CO2 stability field (H/O < 2), 1.5 +/- 0.5% at the H2O maximum, and 6.5 +/- 1% in pure C-H fluids. Molar C2H6 ranges from <0.05% at the H2O maximum to 2% in a pure C-H fluid. Molar H2/C2H6 and H2/CH4 are independent of the bulk H/O of the fluid over a wide range in H/O, indicating that internal reaction rates amongst fluid species are faster than H2 loss. Experiments quenched with variable cooling rates show that CHO fluids preserve their high pressure-temperature species distribution during quenching, provided maximum quench rates are employed.