Detrital fission-track analysis and sedimentary petrofacies as keys of alpine exhumation: The example of the Venetian foreland (European Southern Alps, Italy)

Sedimentary petrography and detrital apatite fission-track analysis of sediments from the Oligo-Miocene Venetian foreland succession (NE Italy) reveal a multi-stage evolution of the Alpine source areas. During the first stage of sedimentation (Chattian to Langhian), the foreland basin was filled by sediments derived from erosion of mainly crystalline Austroalpine units exhumed north of the Periadriatic Lineament. These sediments are characterized by litharenites with mean quartz content of about 61 % and by a mean detrital apatite fission-track peak of about 30 Ma. The Permian-Paleogene sedimentary cover of the Southalpine crystalline basement (Dolomite region) was bypassed by the sediments and made only a minor input. From the Serravallian onwards, the foreland basin was incorporated into the Southalpine thrust belt. The compressional events of the Valsugana phase resulted in thrusting and uplift of the Southalpine domain, as documented by Tortonian fission-track ages in the hanging wall of the major regional thrust (Valsugana thrust fault). The Southalpine crystalline basement, unaffected by Alpine metamorphism, and its sedimentary cover became the main source of sediments, as revealed by the increase in extrabasinal carbonate grains and detrital apatite grains with Late Triassic-Jurassic fission-track ages. During this final stage of basin evolution, about 3000 m of sediments were deposited. These strata subsequently have been uplifted and eroded since the Pliocene, indicating a southward migration of the Alpine deformation front.