Cathodoluminescence, fluid inclusion and stable C-O isotope study of tectonic breccias from thrusting plane of a thin-skinned calcareous nappe

Basal hydraulic breccias of alpine thin-skinned Muran. nappe were investigated by means of cathodoluminescence petrography, stable isotope geochemistry and fluid inclusions analysis. Our study reveals an unusual dynamic fluid regime along basal thrust plane during final episode of the nappe emplacement over its metamorphic substratum. Basal thrusting fluids enriched in O-18, silica, alumina, alkalies and phosphates were generated in the underlying metamorphosed basement at epizonal conditions corresponding to the temperatures of 400-450 degrees C. The fluids fluxed the tectonized nappe base, leached evaporite-bearing formations in hangingwall, whereby becoming oversaturated with sulphates and chlorides. The fluids further modified their composition by dedolomitization and isotopic exchange with the host carbonatic cataclasites. Newly formed mineral assemblage of quartz, phlogopite, albite, potassium feldspar, apatite, dravite tourmaline and anhydrite precipitated from these fluids on cooling down to 180-200 degrees C. Finally, the cataclastic mush was cemented by calcite at ambient anchizonal conditions. Recurrent fluid injections as described above probably enhanced the final motion of the Muran. nappe.