Constraints on Transport and Kinetics in Hydrothermal Systems from Zoned Garnet Crystals

Science  28 Jan 1994:
Vol. 263, Issue 5146, pp. 505-508
DOI: 10.1126/science.263.5146.505


Zonation of oxygen isotope ratios, fluorine, and rare earth element abundances across garnet crystals from the Permian Oslo Rift reflect temporal variation of the hydrothermal system in which the garnets grew. A sharp rimward decrease in the 18O/16O ratio (of 5 per mil) across the interface between aluminum-rich garnet cores and iron-rich rims indicates influx of meteoric fluids to a system initially dominated by magmatic fluids. This influx may record the transition from ductile to brittle deformation of the hydrothermally altered rocks. In contrast, fluorine and light rare earth element concentrations increase at the core-rim interface. These data may reflect enhanced advective transport and notable kinetic control on trace element uptake by the garnets during brittle deformation.