Abstract

In this work petrographic and geochemical analyses allowed us to construct a genetic model of the pervasive dolomitization in the reference section of the Castel Manfrino Dolostones which includes the dolomitized Calcare Massiccio platform and the basinal Corniola sediments (Liassic). Cathodoluminescence and SEM analysis indicates a multiphase dolomitization: an initial calcite replacement (Dolomite 1) followed by recrystallization (Dolomite 2) and cementation events (Dolomite 3), and precipitation of saddle dolomite (Dolomite 4). Carbon and oxygen isotopic data suggest that dolostones underwent several recrystallization and stabilization events under increasing temperatures, in the presence of sea-water derived fluids. Fluid inclusion analyses established that Dolomite 3 took place at temperatures of around 70 degrees C, and Dolomite 4 precipitated at temperatures up to 132 degrees C. The fluid inclusions show salinity values for Dolomite 4 (average 16% NaCl equivalent) higher than Dolomite 3 (average 12%) suggesting a change in fluid geochemistry through time. The burial history, reconstructed from regional data and the succession outcropping in the Montagna dei Fiori area, enables us to match the diagenetic phases with the geological evolution of the area. The shallow burial phase of dolomitization (Dolomite 1) could have occurred during burial from the Upper Jurassic to the Middle Cretaceous. The second dolomitization phase (Dolomite 3), took place starting from the Middle Miocene, when the Lower Jurassic series reached temperatures of about 70 degrees C. After this period the area was subject to the Apennine thrusting, and hydrothermal fluids (with temperatures of 110-130 degrees C) arriving from deep seated faults are believed to have been the dolomitizing fluids for the last event (Dolomite 4).

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