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Keller, J.
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Keller, J.
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- PublicationRestrictedStratigraphy and significance of Brown Tuffs on the Aeolian Islands (southern Italy)(2008-10)
; ; ; ; ; ; ;Lucchi, F.; Università di Bologna, Dipartimento di Scienze della Terra e Geologico-Ambientali ;Tranne, C. A.; Università di Bologna, Dipartimento di Scienze della Terra e Geologico-Ambientali ;De Astis, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Keller, J.; Institut für Mineralogie, Petrologie und Geochemie, Albert-Ludwigs-Universität Freiburg ;Losito, R. ;Morche, W.; ; ; ; ;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.1689 32 - PublicationRestrictedEruptive history and magmatic evolution of the island of Salina (central Aeolian archipelago)(Geological society of London memoir 32, 2013)
; ; ; ; ; ; ; ; ; ; ; Stratigraphic, structural, volcanological and geochemical data allow a detailed reconstruction of the geological history of the island of Salina (central Aeolian sector). Its subaerial volcanism (c. 244 ka to 15.6 ka) developed through six successive Eruptive Epochs interrupted by major quiescence periods, volcano-tectonic collapses and recurrent episodes of marine terrace formation during MIS 7 and MIS 5. Several stratovolcanoes were constructed by strombolian and effusive (Pizzo Capo, Monte Rivi, Monte Fossa delle Felci, Monte dei Porri) to hydromagmatic and subplinian (Monte dei Porri, Pollara) activity, with a general east–west shift of active vents, controlled primarily by the dominant NNW–SSE and minor NE–SW regional tectonic trends, and a progressive chemical differentiation of the erupted products from calc-alkaline basalts to rhyolites. The magma compositions and variations through time are the result of contamination of primary magmas derived from a subduction-modified mantle source with the Calabro–Peloritano lower crust and subsequent differentiation dominated by polybaric fractional crystallization. Magma mixing and mingling processes occurred during individual eruptions. The early basalts were fed from deep reservoirs located near the crust–mantle boundary, whereas the later andesitic to dacitic and, ultimately, rhyolitic magmas originated through combined assimilation and fractional crystallization processes in magma reservoirs at mid- to upper-crustal levels.54 1 - PublicationOpen AccessEruptive, volcano-tectonic and magmatic history of the Stromboli volcano (north-eastern Aeolian archipelago)(Geological society of London memoir 37, 2013)
; ; ; ; ; ; ; ; ; Stromboli is famous for its persistent volcanic activity consisting of periodic discrete explosions alternating with lava effusion and more violent explosions. This paper presents a detailed reconstruction of the geological history of Stromboli and description of the characteristics and distribution of the volcanic units and structural features. Six main growth stages (Eruptive Epochs 1–6), in addition to the c. 200 ka activity of Strombolicchio, are recognized between c. 85 ka and the present day, displaying a magma composition ranging from calc-alkaline to potassic series which usually varies with changing Eruptive Epochs. The Epochs are subdivided into sequences of eruptions and characterized by dominant central-vent summit activity with episodic phases of flank activity along fissures and eccentric vents. The activity was repeatedly interrupted by erosional and destructive phases driven by recurrent vertical caldera-type (cc1–5) and sector (and flank) collapses (sc1–7) and generally associated with significant quiescences. The different serial character of the Stromboli rocks is associated with largely variable trace element contents and isotope ratios. These petrochemical characteristics together with our new stratigraphy indicate that magmas, generated in a heterogeneous mantle wedge, underwent complex differentiation processes during their ascent. Magmas are characterized by polybaric evolution residing in small magma reservoirs that are alternatively tapped by the different collapses.61 328