40Ar/39Ar single crystal dates from pyroclastic deposits provide a detailed record of the 590–240 ka eruptive period at the Vulsini Volcanic District (central Italy)

Abstract

We analyze the age distribution provided by 113 sanidine crystals separated from six samples of pyroclastic products of the Bolsena-Orvieto phase of activity at the Vulsini Volcanic District, which were dated via the 40Ar/39Ar single crystal, total fusion method in a previous study. Moreover, we investigate the compositional and depositional features of the dated products, both at the outcrop scale and at the optical microscope, aimed at discriminating the juvenile vs. antecrystic vs. xenocrystic origin of the dated crystals. Results of this study provide insights on the magmatic process preceding the eruptions, as well as on the eruptive mechanisms of the primary deposits. The data also provide a geochronologic context to the his- tory of eruptive activity of the Vulsini Volcanic District, from 590 to 250 ka with greater detail than previously outlined by direct dating of several primary units. Indeed, most of the six samples analyzed in the present work yielded 19 distinct crystal population ages, 10 of which match those of previously dated eruptive units and the other 9 possibly corresponding to primary deposits so far undated.