ROLE OF MAGMA MIXING DURING THE RECENT ACTIVITY OF LA FOSSA DI VULCANO (AEOLIAN ISLANDS, ITALY)

Relatively homogeneous trachytes have been erupted for approximately 3800 years at la Fossa di Vulcano. From the Punte Nere eruptive cycle up to the Palizzi cycle the products varied little, while after the Palizzi cycle (1600 + 1000 a B.P.) to the latest eruption, 1888-1890 AD, a spectrum of compositions, with rhyolite dominating, characterized the erupted products. A stratigraphic sequence, starting with the Palizzi lava flow, has been studied, focussing the attention on lavas and volcanic bombs, to define the role that magma mixing processes have played in the recent history of La Fossa di Vulcano. Textural and chemical analyses of whole rocks, glass, groundmass, and mineral phases indicate that only the breadcrust bombs, erupted during the 1888-1890, show evidence of mixing between trachylic and rhyolitic end-members. Interestingly, in the deposits of the same eruption, trachytic bombs also occur. The lava flows erupted before 1888-1890 display general features suggesting that they entrained crystals and lava fragments during magma ascent. During the 1888-1890 eruption the trachytic bombs were erupted before the breadcrust bombs, which have a more evolved and hybrid composition. These characteristics, together with the change of the nature of the products after the Palizzi cycle, require a complex volcanological model for the recent history of la Fossa di Vulcano.