O isotope zoning in garnet and staurolite: evidence for closed-system mineral growth during regional metamorphism

Two garnet crystals and one staurolite mineral block obtained from a metapelitic schist, and another garnet mineral block from an amphibolite at the Cordillera Darwin metamorphic complex, Chile, South America, are microanalyzed to determine the oxygen isotope ratio. The complex garnet-biotite-staurolite-plagioclase-muscovite-quartz-ilmenite chlorite constitutes the crystals. The experimental investigation was performed at pressure-temperature conditions of 575 degrees Celsius and 7 kilobars. Laser extraction systems were used for the collection of oxygen isotopes. The core of the minerals had 3.5% more O-18 than the surfaces.