Datability of Quaternary volcanic rocks: an 40Ar/39 Ar perspective on age conflicts in lavas from the Alban Hills, Italy.
Villa, Igor M.
European Journal of Mineralogy Volume 4 Number 2 (1992), p. 369 - 384
published: Apr 21, 1992
manuscript accepted: Jul 3, 1991
manuscript received: Apr 27, 1990
ArtNo. ESP147050402011, Price: 29.00 €
Abstract High-resolution 40Ar/39Ar dating experiments on four leucites from lavas and scoriae of the Alban Hills, recently reported to have 230Th/238U ages between 7 and 25 ka, fail to confirm these young age assignments. Plateau and isochron ages are concordant and consistent with the previously known history of the volcano: 355, 283, 250, and 30-40 ka. A historic Vesuvius lava flow, analysed as a control sample, correctly yields a < 19 ka age, corresponding to a saddle minimum. From the consistency of the 40Ar/39Ar data it is concluded that these rocks do not fulfill the requirements for 230Th/238U dating, probably because they interacted with the LILE-enriched fluids known to have affected the entire Roman Volcanic Province. Sample N-2 is shown to have undergone enrichment both in 40Ar and 87Sr. Major amounts of magma were not produced during the Holocene in the Alban Hills ; the city of Rome is not exposed to an increased volcanic risk.