Testing the validity of organic and inorganic thermal indicators in different tectonic settings from continental subduction to collision: the case history of the Calabria-Lucania border (southern Apennines, Italy)

This paper investigates the applicability of organic and inorganic thermal parameters in a range of thermal conditions, from diagenesis to epizone, and in HP-LT settings within the framework of continental subduction and exhumation in the southern Apennines, where independent thermobarometric constraints are available. Two juxtaposed tectonic units, the HP-LT Lungro-Verbicaro Unit (in the hanging wall) and the non-metamorphic Pollino-Ciagola Unit (in the footwall) have been analysed. For the Lungro-Verbicaro Unit, clay mineral thermal parameters and vitrinite reflectance underestimate metamorphic conditions (constrained by petrology), suggesting that, in relatively HP units, these indicators are 'retarded' and strongly depend on P-T evolution through time. On the other hand, the K-white mica b cell dimension provides a robust estimate of peak pressure. Fluid inclusion textures indicate a fast isothermal decompression during exhumation. Two-phase inclusions from early stage syntectonic veins were trapped after isothermal exhumation at a pressure of 0.3 GPa. For the Pollino-Ciagola Unit, the correlation of analysed parameters effectively unravels the thermal evolution, with maximum palaeotemperatures of c. 150 degrees C. Apatite fission tracks provide details of the final stages of exhumation, indicating that both units were coherently exhumed in the Late Miocene, following the tectonic emplacement of the Lungro-Verbicaro Unit on top of the Pollino-Ciagola Unit.