NAC2024 - "Isotopic signatures of fluid inclusions from Variscan quartz veins using a novel CRDS approach"

Fluid-inclusions in quartz veins play a crucial role to determine the pathways of fluid flow in the subsurface. Here, we present a novel approach to analyse the isotopic composition of water fluid inclusions using Cavity Ring-Down Spectroscopy (CRDS). The CRDS is interfaced with a mechanical crusher to liberate fluid inclusion water from host mineral at ~120oC. The water vapour of the crushed sample is added to a moisturized nitrogen gas background, which has constant isotopic composition and constant concentrations, which has been achieved by precisely temperature-controlled evaporation unit box that is developed by the Earth Science Stable Isotope Laboratory at the Vrije Universiteit Amsterdam (VU).
This newly developed setup provides reliable and consistent paired oxygen and hydrogen isotopic composition from quartz minerals. For this study, we analysed quartz veins samples from two different locations (Germany, Portugal) from NW Europe related to Variscan orogeny. These isotopes data align with modern Global Meteoric Water Line (GMWL) indicating meteoric waters in fold-and-thrust belt. Complementary, silicon and oxygen isotopic signature of quartz host minerals and microthermometry data reveals that hydrothermal system cooling down with meteoric water in different time. This method directly measures quartz vein fluid inclusions isotopic compositions, faster and more efficiently than conventional methods.