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Geochemical and isotopic insights into the assembly,evolution and disruption of a magmatic plumbing system before and after a cataclysmic caldera-collapse eruption at Ischia volcano (Italy) |
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| Authors: | R J Brown L Civetta I Arienzo M D’Antonio R Moretti G Orsi E L Tomlinson P G Albert M A Menzies |
| Institution: | 1. Department of Earth Sciences, Science Labs, Durham University, Durham, DH1 3LE, UK 2. Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse, Università degli Studi di Napoli Federico II, Largo S. Marcellino, 80138, Naples, Italy 3. Sezione di Palermo, Istituto Nazionale di Geofisica e Vulcanologia, Via Ugo La Malfa 153, 90146, Palermo, Italy 4. Sezione di Napoli-Osservatorio Vesuviano, Istituto Nazionale di Geofisica e Vulcanologia, Via Diocleziano 328, 80124, Naples, Italy 5. Dipartimento di Ingegneria Civile, Design, Edilizia e Ambiente, Seconda Università di Napoli, Via Roma 29, 81031, Aversa, CE, Italy 6. Department of Geology, Saint Mary’s University, 923 Robie Street, Halifax, NS, Canada 7. Dipartimento di Fisica “E. R. Caianiello”, Università degli Studi di Salerno, Via Giovanni Paolo II 132, 84084, Fisciano, SA, Italy 8. Department of Geology, Trinity College Dublin, College Green, Dublin, Ireland 9. Department of Earth Sciences, Royal Holloway University of London, Egham Hill, Egham, Surrey, TW20 0EX, UK |
| Abstract: | New geochemical and isotopic data on volcanic rocks spanning the period ~75–50 ka BP on Ischia volcano, Italy, shed light on the evolution of the magmatic system before and after the catastrophic, caldera-forming Monte Epomeo Green Tuff (MEGT) eruption. Volcanic activity during this period was influenced by a large, composite and differentiating magmatic system, replenished several times with isotopically distinct magmas of deep provenance. Chemical and isotopic variations highlight that the pre-MEGT eruptions were fed by trachytic/phonolitic magmas from an isotopically zoned reservoir that were poorly enriched in radiogenic Sr and became progressively less radiogenic with time. Just prior to the MEGT eruption, the magmatic system was recharged by an isotopically distinct magma, relatively more enriched in radiogenic Sr with respect to the previously erupted magmas. This second magma initially fed several SubPlinian explosive eruptions and later supplied the climactic, phonolitic-to-trachytic MEGT eruption(s). Isotopic data, together with erupted volume estimations obtained for MEGT eruption(s), indicate that >5–10 km3 of this relatively enriched magma had accumulated in the Ischia plumbing system. Geochemical modelling indicates that it accumulated at shallow depths (4–6 km), over a period of ca. 20 ka. After the MEGT eruption, volcanic activity was fed by a new batch of less differentiated (trachyte-latite) magma that was slightly less enriched in radiogenic Sr. The geochemical and Sr–Nd-isotopic variations through time reflect the upward flux of isotopically distinct magma batches, variably contaminated by Hercynian crust at 8–12 km depth. The deep-sourced latitic to trachytic magmas stalled at shallow depths (4–6 km depth), differentiated to phonolite through crystal fractionation and assimilation of a feldspar-rich mush, or ascended directly to the surface and erupted. |
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