Upper Miocene volcanic ash layers from central Italy: looking for the missing eruption.

Abstract

The Mediterranean region has been characterized by intense explosive volcanism since the Eocene. These eruptions ejected tephra, including fine grained ash, which were thrown into the air and dispersed over wide areas to later be deposited as ash layers, many of which are preserved in some continental and marine sedimentary basins. Their study provides crucial insights into past volcanic activity, yet, for many of such ash layers, the understanding of their sources remains challenging. The presence of many ash layers across central Italy is widely recognized in literature although not uniquely associated with a specific volcanic source. We investigate in detail upper Tortonian (∼7.6 Ma) ash layers sampled from three different localities, from the Tyrrhenian to the Adriatic coast of Italy, comparing our results with others already described in the literature. Electron microprobe geochemical analyses on biotite crystals, U-Pb ID-TIMS and LA-ICP-MS geochronological dating and trace elements / Lu-Hf isotope analyses on zircons permitted us to expand our knowledge of these ancient ash deposits. Several potential volcanic centers were active during the late Tortonian, including the Massif Central (France), the Valencia trough (Spain), the Betics-Rif orogen (Spain-Morocco), and eastern Carpathians (Romania)and Capraia island (Italy). Through detailed radioisotopic dating and geochemical comparisons, we narrow down the possible source to the Upper Miocene Capraia island volcano (Tuscan archipelago), located in the northern Tyrrhenian basin.