Wouter Heijlen

Origin and geochemical evolution of synsedimentary, syn- and post-tectonic high-salinity fluids at the Variscan thrust front in Belgium

Abstract Microthermometric and crush-leach analyses of fluid inclusions in a number of minerals that formed before, during and after the Variscan orogeny at the Variscan thrust front in Belgium, indicate that the fluids all originated from the evaporation of seawater during the Middle and Late Palaeozoic. Migration of these brines into the subsurface caused the dolomitisation of the surrounding limestones. Their expulsion during the Frasnian and during the Variscan orogeny caused the formation of, respectively, synsedimentary barites and syntectonic zebra-dolomites. Parts of the brine, however, migrated further down into the basement where they interacted with Lower Palaeozoic to Lower Devonian rocks. These fluids were finally expelled along extensional and strike-slip faults during several periods in the Mesozoic.