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. Twophase 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°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. © 2010 Geological Society of London.