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Forecasting the duration of volcanic eruptions: an empirical probabilistic model |
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| Authors: | L S Gunn S Blake M C Jones H Rymer |
| Institution: | 1. Istituto Nazionale di Geofisica e Vulcanologia (INGV), Osservatorio Etneo, Sezione di Catania, Piazza Roma, 2, 95125, Catania, Italy 2. Dipartimento di Scienze della Terra e del Mare (DISTeM), Università di Palermo, Via Archirafi, 22, 90123, Palermo, Italy 3. Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione di Palermo, Via U. La Malfa, 153, 90146, Palermo, Italy 4. Eni SpA, E&P Division, Via Emilia, 1, San Donato Milanese, 20097, Milan, Italy |
| Abstract: | Various xenoliths have been found in lavas of the 1763 (“La Montagnola”), 2001, and 2002–03 eruptions at Mt. Etna whose petrographic evidence and mineral chemistry exclude a mantle origin and clearly point to a cognate nature. Consequently, cognate xenoliths might represent a proxy to infer the nature of the high-velocity body (HVB) imaged beneath the volcano by seismic tomography. Petrography allows us to group the cognate xenoliths as follows: i) gabbros with amphibole and amphibole-bearing mela-gabbros, ii) olivine-bearing leuco-gabbros, iii) leuco-gabbros with amphibole, and iv) Plg-rich leuco gabbros. Geobarometry estimates the crystallization pressure of the cognate xenoliths between 1.9 and 4.1 kbar. The bulk density of the cognate xenoliths varies from 2.6 to 3.0 g/cm3. P wave velocities (V P ), calculated in relation to xenolith density, range from 4.9 to 6.1 km/s. The integration of mineralogical, compositional, geobarometric data, and density-dependent V P with recent literature data on 3D V P seismic tomography enabled us to formulate the first hypothesis about the nature of the HVB which, in the depth range of 3–13 km b.s.l., is likely made of intrusive gabbroic rocks. These are believed to have formed at the “solidification front”, a marginal zone that encompasses a deep region (>5 km b.s.l.) of Mt. Etna’s plumbing system, within which magma crystallization takes place. The intrusive rocks were afterwards fragmented and transported as cognate xenoliths by the volatile-rich and fast-ascending magmas of the 1763 “La Montagnola”, 2001 and 2002–03 eruptions. |
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