40Ar/39Ar isotopic dating of Etna volcanic succession

Emanuela De Beni(*), Stefano Branca(*), Mauro Coltelli(*), Gianluca Groppelli(**) & Jan R. Wijbrans(***)
(*) Istituto Nazionale di Geofisica e Vulcanologia, Osser - vatorio Etneo, sezione Catania, Piazza Roma, 2 - 95123 Catania (Italy). Corresponding authors: phone: +390957165822; e_mail: emanuela.debeni@ct.ingv.it (**) C.N.R - Istituto per la Dinamica dei Processi Ambientalisezione di Milano, Via Mangiagalli, 34 - 20133 Milano (Italy). (***) Faculty of Earth and Life Sciences, VU University, Amsterdam (The Netherlands).

Since the 1970's, about 50 radio-isotopic ages have been determined on Etna volcanics using different techniques: Th-U and K/Ar. Unfortunately, these ages cannot be readily used to constrain the new stratigraphic setting of the volcano, because of the uncertainty in sample locations or, sometimes, the large errors affecting the calculated ages. For this reason a program of radio-isotopic dating applying the 40Ar/39Ar incremental heating technique to date the groundmass of basaltic samples has been carried out from 2002. Forty samples (22 of which are of new publication) were collected from key outcrops on Etna volcano, selected on the basis of their stratigraphic position, while one sample was collected from the Hyblean plateau volcanics. We have obtained reliable results from all volcanics analysed from 542 ka up to 10 ka with the MSWD's (Mean Square of Weighted Deviates) ranging from 0.03 up to 1.7 excluding IS sample (MSWD = 6.28). These new results allow us to: i) assign an age to 19 of the 25 lithostratigraphic units defined in the new geological map of Etna volcano; ii) clarify the uncertain stratigraphic position of isolated volcanic units; iii) constraint the temporal hiatus that matches the main unconformities; iv) outline the lapse of time between the end of the Hyblean volcanism and the beginning of eruptive activity in the Etna region.

Etna volcano, 40Ar/39Ar geochronology, volcanic succession.