Persisting Rock-Buffered Conditions in the Upper Triassic and Lower Jurassic Dolomites of the Central Apennines (Italy) During Diagenesis, Burial, and Thrusting

Basin-scale dolomitization of carbonate sequences occurs over long time spans and results from diagenesis, burial, and tectonically driven fluid fluxes. Depicting the different geological processes producing dolomitized carbonate sequences requires combining accurate field, petrographic, and geochemical analyses. Here, we investigate the dolomitization processes in carbonates of the Norian to Toarcian age exposed in the Gran Sasso Massif, Central Apennines of Italy, by integrating field observations, standard and CL petrography, carbon, oxygen, strontium and clumped isotopes, minor elements, and X-ray diffractometry. The carbonates show pervasive replacive dolomitization, and dolomite cements are observed in bed-parallel and thrust-related veins. Replacive dolomites show incomplete replacement from modified seawater in oxidizing conditions, with minimum temperatures of 40–65 °C and a 87Sr/86Sr lower than coeval seawater. The first dolomitization event started at shallow burial in the Late Triassic–Early Jurassic and was later affected by replacement at intermediate burial depths. Bedding-parallel dolomite veins crystallized due to fluid overpressures at deep burial depths in a rock-buffered system without variations in geochemistry. Fault-related dolomites cemented thrust-related fractures during compressional deformation in the Messinian–Early Pliocene from seawater modified by mixing with external fluids. Precipitation temperatures of replacive, bedding-parallel, and fault-related dolomite veins are similar. Despite the dolomite types being characterized by different textures and petrographic features, rock-buffered conditions resulted in insignificant variations of their geochemical properties.