A new approach to geobarometry by combining fluid inclusion and clumped isotope thermometry in hydrothermal carbonates

This study presents a new approach to geobarometry by combining fluid inclusion and clumped isotope (Δ47) thermometry on carbonate minerals. The offset between homogenisation temperatures of primary fluid inclusions with known composition and Δ47 temperatures of the host mineral allows a direct estimation of the fluid pressure at the time of carbonate crystallisation. This new approach is illustrated via hydrothermal dolomite samples from the Variscan foreland fold-and-thrust belt in northern Spain. Clumped isotope analyses yield crystallisation temperatures (107–168°C) which are higher than homogenisation temperatures in corresponding samples (95–145°C). The calculated pressure values suggest that dolomitizing fluids were overpressured during formation of zebra dolomite textures, whereas lower pressures are obtained for dolomite cement from breccia textures. This new approach to geobarometry opens up the possibility of estimating the pressure of carbonate crystallisation and has potential applications in diagenesis, basin analysis, ore geology and tectonics.