Thermal maturation of the lower Palaeozoic 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 assessment of the thermal history of Lower Palaeozoic strata in the southwestern margin of the Malopolska Massif, along the contact with the Upper Silesian Massif. The CAI data provide no evidence for a previously suggested greenschist-grade regional metamorphism in the Cracow-Myszkow zone during the Caledonian epoch. Near Zarki, the Silurian rocks display a relatively uniform thermal overprint (CAI values of 4) resulting from sedimentary burial during the early Late Carboniferous. The estimated maximum temperatures of 200-220 degrees C can be explained by an elevated heat flow associated with the Cracow Fault system. This thermal maturation level was locally enhanced (CAI values up to 8) after the Westphalian, due to the magmatic activity caused by the Variscan regional extension.