~(40)Ar/~(39)Ar and ~(14)C geochronology of the Albano maar deposits: Implications for defining the age and eruptive style of the most recent explosive activity at Colli Albani Volcanic District, Central Italy

摘要

New ~(40)Ar/~(39)Ar and ~(14)C ages have been found for the Albano multiple maar pyroclastic units and underlying paleosols to document the most recent explosive activity in the Colli Albani Volcanic District (CAVD) near Rome, Italy, consisting of seven eruptions (Albano 1 = oldest). Both dating methodologies have been applied on several proximal units and on four mid-distal fall/surge deposits, the latter correlated, according to two current different views, to either the Albano or the Campi di Annibale hydromagmatic center. The ~(40)Ar/~(39)Ar ages on leucite phenocrysts from the mid-distal units yielded ages of ca. 72 ka, 73 ka, 41 ka and 36 ka BP, which are indistinguishable from the previously determined ~(40)Ar/~(39)Ar ages of the proximal Albano units 1,2, 5 and 7, thus confirming their stratigraphic correspondence.rnTwenty-one ~(14)C ages of the paleosols beneath Albano units 3, 5, 6 and 7 were found for samples collected from 13 proximal and distal sections, some of which were the same sections sampled for ~(40)Ar/~(39)Ar measurements. The ~(14)C ages were found to be stratigraphically inconsistent and highly scattered, and were systematically younger than the ~(40)Ar/~(39)Ar ages, ranging from 35 ka to 3 ka. Considering the significant consistence of the ~(40)Ar/~(39)Ar chronological framework, we interpret the scattered and contradictory ~(14)C ages to be the result of a variable contamination of the paleosols by younger organic carbon deriving from the superficial soil horizons.rnThese results suggest that multiple isotopic systems anchored to a robust stratigraphic framework may need to be employed to determine accurately the geochronology of the CAVD as well as other volcanic districts.