Relation between Diagenetic Evolution and Tectonic Regimes in Thrust-fold Belt – The Calcari Grigi Group, Jurassic, Asiago Plateau, Northern Italy

Dolomitization and dolomite cements precipitation in Jurassic platform carbonates has been studied from outcrop samples of the Calcari Grigi Group (eastern Southern Alps, northern Italy). In the studied area various types of dolomites can be described at all scales of observation. On outcrops, primary dolomite can be recognised only in some stratigraphic intervals. By contrast, pervasive replacive dolomites are widespread throughout the area, mostly confined in the central and lower part of the sequence. The collected data demonstrate that the massive dolomite replacement was followed by a multiphase precipitation of dolomite and late calcite cements. The replacement occurred during burial, into a passive margin regime, due to compaction driven flow of formational fluids. Conversely, fluid inclusions data crossed with thermal history prove that dolomite and calcite cements precipitated when the study area was involved in collisional tectonics. Fluid inclusions data display a decreasing salinity trend from sea water to freshwater fluids. This observed dilution of fluids can be related to the infiltration of meteoric waters from the emerging Alpine chain. These data proof useful to interpret the diagenetic evolution of the unit as related to the evolution of the hydrogeological system in relation with the tectonic regime of the area.