New results of 40 Ar/ 39 Ar dating constrain the timing of transition from fissure-type to central volcanism at Mount Etna (Italy) Emanuela De Beni, 1 Jan R. Wijbrans, 2 Stefano Branca, 3 Mauro Coltelli 3 and Gianluca Groppelli 4 1 Dipartimento di Scienze Geologiche, Universita ` di Catania, Corso Italia 55, 95129 Catania, Italy; 2 Faculteit der Aardwetenschappen, Vrije Universiteit, Amsterdam, The Netherlands; 3 Istituto Nazionale di Geofisica e Vulcanologia-Sezione di Catania, Piazza Roma 2, 95123 Catania, Italy; 4 Istituto per la Dinamica dei Processi Ambientali-Sezione di Milano, CNR, via Mangiagalli 34, 20133 Milano, Italy Introduction Etna, the highest active volcano in Europe situated on the eastern coast of Sicily, southern Italy, is renowned for its frequent and spectacular erup- tions (Fig. 1). The earliest geological studies of Etna volcano were performed during the first half of the nineteenth century and contributed to the first geological map of Etna published by Walters- hausen (1880). Only after a century did Rittmann (1973) propose a new geological reconstruction of Etna vol- cano in which five evolutionary stages were defined. This geological setting represented the stratigraphic frame for the Geological Map of Mt Etna pub- lished by Romano at the end of the 1970s (1979, 1982). One of the main limitations of these geological recon- structions was the lack of absolute age determinations necessary to define the time span in which each of the vol- canic centres contributed to the devel- opment of the present volcanic edifice. The first isotopic analyses on Etne- an lavas were performed by Condo- mines and Tanguy (1976) and Condomines et al. (1982) using U– Th disequilibrium techniques. Subse- ABSTRACT Recent geological studies performed at Etna allow reassessing the stratigraphic frame of the volcano where distinct evolu- tionary phases are defined. This stratigraphic reconstruction was chronologically constrained on the basis of a limited number of U–Th and K–Ar age determinations whose uncer- tainty margins are sometimes too wide. For this reason, we successfully adopted at Etna the 40 Ar/ 39 Ar technique that allowed obtaining more precise age determinations. The incremental heating technique also gives information on sample homogeneity, and potential problems of trapped argon. Five samples were collected from stratigraphically well-con- trolled volcanic units in order to chronologically define the transition between the fissure-type volcanism of the Timpe phase to the central volcanism of the Valle del Bove Centers. Isotopic ages with an uncertainty margin of 2–4% have been obtained emphasizing that this transition occurred (130– 126 ka) without significant temporal hiatus. Terra Nova, 17, 292–298, 2005 Fig. 1 Geological framework of the SE flank of Etna volcano (modified after Branca et al., 2004). VdB, Valle del Bove. Correspondence: Dr Emanuela De Beni, Dipartimento di Scienze Geologiche, Uni- versita` di Catania,Corso Italia 55, Catania 95124, Italy. Tel.: +39 0957 165 830; fax: +39 095 435 801; e-mail: debeni@ct.ingv.it 292 Ó 2005 Blackwell Publishing Ltd doi: 10.1111/j.1365-3121.2005.00614.x