Coeval strombolian and vulcanian type explosive eruptions at Panarea (Aeolian islands)

In this paper, we document the evolution of the emergent Panarea dome in the Aeolian islands 14 (Southern Italy), placing particular emphasis on the reconstruction of the explosive events occurred 15 during the final stage of its evolution. Two main pyroclastic successions exposing fall deposits with 16 different compositions have been studied into detail: the andesitic Palisi succession and the basaltic 17 Punta Falcone succession. The close-in-time deposition of the two successions, the dispersal area and 18 grain size distribution of the deposits account for their attribution to vents located in the western sector 19 of the present island and erupting almost contemporaneously. Vents could have been aligned along 20 NNE-trending regional fracture systems controlling the western flank of the dome and possibly its 21 collapse. Laboratory analyses have been devoted to the characterization of the products of the two 22 successions that have been ascribed to vulcanian- and to strombolian-type eruptions respectively. The 23 vulcanian eruption started with a vent-clearing phase that occurred by sudden decompression of a 24 pressurized magma producing ballistic bombs and a surge blast and the development of a vulcanian 25 plume. Vulcanian activity was almost contemporaneous to strombolian type fall-out eruptions. The 26 coeval occurrence of basaltic and andesitic eruptions from close vents and the presence of magmatic 27 basaltic enclaves in the final dacitic lava lobe of the dome allow us to speculate that the intrusion of a 28 basaltic dyke played a major role in triggering explosive eruptions. The final explosive episodes may 29 have been caused by extensional tectonics fracturing the roof of a zoned shallow magma chamber or by 30 the intrusion of a new basaltic magma into a more acidic and shallow reservoir. Intrusion most likely 31 occurred through the injection of dykes along the western cliff of the present Panarea Island inducing 32 the collapse of the western sector of the dome.