Zircon solubility in alkaline aqueous fluids at upper crustal conditions

The measured solubilities of zircon in pure H2O at 600 and 750 °C are only slightly higher than the procedural blank of 3.3 × 10−7m Zr. However, the measured solubility of zircon increases with increasing aqueous silica, suggesting that zirconium complexes with silica in the fluid. At 600 °C linear regression of experimental results yielded: ln(Zr)=0.25+2.9∗ln(Si)where terms in parentheses represent molal concentrations. Zircon solubility also seems to increase with increasing hydroxyl concentration in the fluid. Enhanced solubility in silica-rich, alkaline fluids may cause dissolution-reprecipitation of zircon and resetting of its isotopic clocks, suggesting that some zircon U-Pb ages may correspond to fluid events.