P-T-X variation along a polysulphide mineralised low-angle shear zone in the Lower Palaeozoic Anglo-Brabant fold belt (Belgium)

摘要

Quartz veins with chlorite have been studied in a mineralised low-angle shear zone at the southern border of the Anglo-Brabant fold belt. Pressure and temperature conditions during vein formation were obtained from microthermometry of fluid inclusions in vein quartz and chlorite geothermometry. Mi-crothermometry only shows an increase of salinity with depth through the shear zone. Detailed microscopy and Raman spectroscopy indicate an increase of the CH_4 content in inclusions closely associated with the mineralisation. This enrichment is not concentrated in the most intensely mineralised zones, but occurs in the whole shear zone. Chlorite geothermometry indicates fluid temperatures between 300 ℃ and 420 ℃. The chlorites in the core of the shear zone indicate an increase of their precipitation temperature with ～ 30 ℃. A pressure of 100 to 200 MPa can be deduced from the intersection of the calculated isochores of the H_2O-CO_2-CH_4-NaCl-KCl inclusions with the data from the chlorite geothermometry.