40Ar/39Ar chronostratigraphy of the initial activity in the Sabatini Volcanic Complex (Italy)

The stratigraphy and chronology of the initial activity of the Sabatini Volcanic Complex (SVC) has been studied. 40Ar-39Ar spectra were obtained on 9 sanidine samples representing 4 outcropping unit, each the lowest in a subsector of the SVC. The Morlupo trachyte yielded a plateau age of 587 +/- 9 ka. Four samples from the composite Tufo Giallo della Via Tiberina unit, whose eruptions were mainly hydromagmatic, with a partially subaqueous depositional environment, all yield disturbed spectra and contain variable, but high, contents of excess 40Ar. Its likely eruption period is between 600 and 550 ka. Two samples from the Peperini Listati gave different ages: 449 +/- 6 and <= 437 ka. This result can be explained with the presence of at least two different units in the field. Two samples from Tufo Grigio Sabatino define ages between 430 and 435 ka: we propose an age of 433 +/- 6 ka for this formation.