Isotopic mass balance of metamorphic fluids in the Gogołów-Jordanów serpentinite massif, Lower Silesia, SW Poland

Abstract

This work aims at estimation of the amount of metamorphic fluids which led to the present-day variability of isotopic compositions, δD and δ18O, in serpentinites from the Gogołów–Jordanów Massif. This goal was achieved by means of a numerical model reproducing selected features of geological environment and a computer application supporting this model. The Gogołów–Jordanów Massif consists of peridotites transformed to a different degree into serpentinites and subject to brittle deformation that produced a complex fracture system. The potential tectonic control on the pattern of the fluid migration paths was investigated using palaeostress analysis based on slickenside measurements. Isotopic analyses were carried out for hydrogen and oxygen from serpentine, oxygen from magnetite, and hydrogen and oxygen from carbonates. The variability of δD and δ18O in the serpentinites along the modelled migration paths demonstrates that serpentinization of peridotites was caused by fluids derived from at least three sources revealing different isotopic characteristics. Fluids produced during the magmatic-hydrothermal stage played a major role in serpetinization, since they represent approximately 95% of all fluids interacting with the rock. In contrast, oceanic water represents only 1% of fluids involved in serpenti- nization. The calculated mean amount of fluid required for serpentinization of 1 m3 of peridotite is equal to 98 × 104 kg.