Very low solubility of rutile in H (sub 2) O at high pressure and temperature, and its implications for Ti mobility in subduction zones

The solubility of rutile in H (sub 2) O has been measured at 1000-1100 degrees C, 1-2 GPa. The data indicate very low solubility in the range investigated, with a maximum of 4.7 millimol/kg H (sub 2) O at 1100 degrees , 2 GPa. The data were fitted to the equation log m (sub Ti) = 4.892-10470/T + 0.1923 P, where m (sub Ti) is Ti molality, T is in Kelvins and P in GPa. In comparison to previous results, the new data indicate substantially lower solubility, opposite pressure dependence, and thermodynamic properties of the reaction rutile = TiO (sub 2.aq) that are now consistent with other oxide hydrolysis reactions. Calculations of Ti transport during mantle metasomatism by H (sub 2) O in subduction zone environments predict much lower Ti mobility at all conditions. These results offer strong support for models of Ti retention in eclogites during slab devolatilization, and require examples of significant Ti mass transport to be explained by complexing agents in solution, probably as aluminosilicate comlexes.