Search

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

Abstract: Ash-rich tephra layers interbedded in the pyroclastic successions of Panarea island (Aeolian archipelago, Southern Italy) have been analyzed and related to their original volcanic sources. One of these tephra layers is particularly important as it can be correlated by its chemical and morphoscopic characteristics to the explosive activity of Somma-Vesuvio. Correlation with the Pomici di Base eruption, that is considered one of the largest explosive events causing the demolition of the Somma stratovolcano, seems the most probable. The occurrence on Panarea island of fine ashes related to this eruption is of great importance for several reasons: 1) it allows to better constrain the time stratigraphy of the Panarea volcano; 2) it provides a useful tool for tephrochronological studies in southern Italy and finally 3) it allows to improve our knowledge on the distribution of the products of the Pomici di Base eruption giving new insights on the dispersion trajectories of fine ashes from plinian plumes. Other exotic tephra layers interbedded in the Panarea pyroclastic successions have also been found. Chemical and sedimentological characteristics of these layers allow their correlation with local vents from the Aeolian Islands thus constraining the late explosive activity of Panarea dome. [Copyright &y& Elsevier]

Abstract: Brown Tuffs (BT) are volcaniclastic ash deposits prominently represented in the stratigraphic profiles of all the Aeolian Islands (and Capo Milazzo on the northern coast of Sicily). Detailed stratigraphy and tephrochronology together with available radiometric ages suggest that they were emplaced over a long time interval spanning from the end of the last interglacial period (ca. 80 ka BP) up to 4–5 ka BP (age of the overlying Punte Nere pyroclastic products on Vulcano). The most complete BT succession is documented on Lipari where 14 distinct and successive units are subdivided by the interbedding of widespread tephra layers, local volcanic products, paleosols and epiclastic deposits and the occurrence of local erosive surfaces. Inter-island occurrence of Ischia-Tephra (a widely known tephra layer in the Aeolian archipelago dated at 56 ka BP) and Monte Guardia pyroclastics from Lipari (dated at 22–20 ka BP) subdivides the BT succession in Upper (UBT), Intermediate (IBT) and Lower BT units (LBT), which can be correlated at regional level: the LBT was emplaced between 80 and 56 ka BP, the IBT between 56 and 22 ka BP and the UBT between 20 and 4–5 ka BP. On the basis of stratigraphy, similarity in lithology and textural features, morphology of glass fragments, composition and consistency of thickness and grain-size variations, UBT units correlate with Piano Grotte dei Rossi tuffs on Vulcano island. They were generated by pulsating hydromagmatic explosive activity giving rise to pyroclastic density currents spreading laterally from a source located inside the La Fossa caldera on Vulcano island. Composition is in agreement with this hypothesis since UBT compositional features match those of Vulcano magmas erupted in that period. The effect of co-ignimbrite ash clouds (or associated fallout processes from sustained eruptive columns) is seen to explain the presence of UBT in areas further away from the suggested source (e.g. Salina and Lipari islands and Capo Milazzo). The origin of UBT exposed on Panarea island is still a matter of debate, due to contrasting compositional data. Due to large uniformity of lithological, textural and componentry characters with respect to the UBT, the lower portions of the BT succession (LBT-IBT) are considered to be the result of recurrent, large scale hydromagmatic eruptions of similar type. Moreover, for the IBT units, the correlation with Monte Molineddo 3 pyroclastics of Vulcano island (on the basis of lithological, compositional and stratigraphic matching) again suggests source(s) related to the Vulcano plumbing system and located within the La Fossa Caldera. [Copyright &y& Elsevier]