THERMAL MATURATION OF THE LOWER PALEOZOIC STRATA IN THE SOUTHWESTERN MARGIN OF THE MALOPOLSKA MASSIF, SOUTHERN POLAND - NO EVIDENCE FOR CALEDONIAN REGIONAL METAMORPHISM

Conodont colour alteration index (CAI) values have been used for the a ssessment of the thermal history of Lower Palaeozoic strata in the sou thwestern margin of the Malopolska Massif, along the contact with the Upper Silesian Massif. The CAI data provide no evidence for a previous ly suggested greenschist-grade regional metamorphism in the Cracow-Mys zkow zone during the Caledonian epoch. Near Zarki, the Silurian rocks display a relatively uniform thermal overprint (CAI values of 4) resul ting from sedimentary burial during the early Late Carboniferous. The estimated maximum temperatures of 200-220 degrees C can be explained b y an elevated heat flow associated with the Cracow Fault system. This thermal maturation level was locally enhanced (CAI values up to 8) aft er the Westphalian, due to the magmatic activity caused by the Varisca n regional extension.