ASSESSING THE NATURE OF TECTONIC CONTACTS USING FISSION-TRACK THERMOCHRONOLOGY - AN EXAMPLE FROM THE CALABRIAN ARC, SOUTHERN ITALY

Fission-track thermochronology applied to the nappe pile of the Calabr ian Arc of southern Italy, particularly within the continental basemen t rocks, has provided important new constraints on the nature of some of the tectonic contacts. In southern Calabria an important phase of l ower Miocene crustal extension is indicated. In northern Calabria no O ligocene or younger extension is seen. Here, the emplacement of contin ental basement rocks with Alpine metamorphism over ophiolitic rocks wi th little or no metamorphism is constrained as a thrust of lower to mi ddle Miocene age related to collision of the Calabrian Arc with the Ad ria plate margin. It is proposed that reduction in the plate convergen ce velocity during collision of a retreating subduction zone with a co ntinental margin is, at least partly, an explanation for the onset of extension in southern Calabria during the Miocene.