Magmatic and geodynamic significance of two volcaniclastic deposits in the Oligo-Miocene successions of Southern Apennines (Italy)

Two volcaniclastic deposits, ROC and SBA, in the Oligo-Miocene succession of the Southern Apennines, between Apulia and Campania regions, have been studied for the first time. Mineral composition, SEM-EDS and LA-ICP-MS analyses, for major and trace elements, respectively, allowed recognising magmatic products of typical calc-alkaline to high-K calc-alkaline affinity. ROC glasses have a restricted com- positional range in the rhyolitic field whereas SBA glasses show a wide compositional range from andesite to rhyolite, with dacite as the most common composition. Fission track dating of apatite in the SBA de- posits yielded an age of 21.7 ± 2.2 Ma, which is comprised between the Chattian and the Burdigalian. Biostratigraphic analyses in sedimentary layers adjacent to ROC layers indicate they were deposited not before Burdigalian. A provenance analysis of the studied volcaniclastics in relation to the possible source areas of the Mediterranean and neighbour- ing areas was performed. On the basis of time constraints, mineral and trace element composition a convincing correlation of the ROC deposits with potential source areas did not emerge. Instead, a provenance from the southwestern and northwestern Sardinian volcanic centres was favoured for the SBA volcaniclastic deposits. This hypothesis is compatible with the Oligo-Miocene paleogeographic reconstructions, that show the proximity of the Apennine sedimentary basins to Sardinia before the opening of the Tyrrhenian sea