Stable hydrogen isotope compositions of tourmalines from the Sopron metamorphic complex: Metamorphic closure temperature and fluid composition

Abstract

AbstractStable hydrogen isotope compositions of metamorphic rocks and minerals can provide information on the origin of metamorphic fluids, which is especially important in systems that had experienced multiple metamorphic events. The Sopron orthogneiss-micaschist complex is a good target as it records signs of Variscan and Alpine metamorphic events as well as Variscan granitic magmatism. In this study tourmaline-bearing rocks (pegmatitic orthogneisses and kyanite-chlorite-muscovite schists) of the Sopron metamorphic complex were sampled and their tourmaline grains were analyzed for stable hydrogen isotope compositions (δ2H). The δ2H values (−23 ± 1‰, relative to V-SMOW) are in accordance with a fluid flux from devolatilization of subducted, seawater-containing rocks. Tourmaline-chlorite hydrogen isotope fractionations correspond to about 550 °C, indicating that δ2H values formed close to peak metamorphic temperatures are preserved without retrograde isotope exchange during cooling.