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Constraining pre- and syn-eruptive conditions and processes of the Montagnone eruptive sequence (Ischia, Italy): Implications for transitions in eruptive style in trachytic magmatic systems

Loïc Maingault1 , Carlo Pelullo2, Hélène Balcone-Boissard3, Fabio Arzilli1, Ilenia Arienzo2, Sumit Chakraborty4, Sandro de Vita2, Fabio Sansivero2

  • Affiliations:  1Universita\' di Camerino, Scuola di Scienze e Tecnologie, sezione Geologia, Via Gentile III da Varano, 62032 Camerino (MC), Italia 2 Istituto Nazionale di Geofisica e Vulcanologia, sezione di Napoli Osservatorio Vesuviano, via Diocleziano 328, 80124, Napoli, Italy 3 Sorbonne Université, CY Cergy Paris Université, CNRS INSU, Institut des Sciences de la Terre de Paris, ISTeP, F-75005 Paris, France 4 Institut für Geologie, Mineralogie und Geophysik, Ruhr Universität, Universitätsstraße, 150, 44801, Bochum, Germany 

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 210

  • Programme No: 3.2.33

  • Theme 3 > Session 2

Abstract

Over the last 10 ka, the eastern sector of Ischia island has experienced volcanic eruptions with a wide range of eruptive styles. Since this area is densely populated, volcanic risk is high, making quantitative insights on how pre-eruptive conditions could control eruptive styles essential for future risk mitigation strategies. We aim to understand how pre-eruptive conditions control such variations in eruptive styles. The Montagnone eruptive sequence (2.4-0.9 ka) is characterised by homogeneous trachytic magma compositions and identical mineral assemblages throughout its eruptions. This eruptive sequence shows transitions in eruptive styles, ranging from lava dome formation to sub-Plinian eruptions. In this work, we analyse the textures and chemical compositions of the juvenile fragments and mineral phases from the Montagnone sequence. Clinopyroxene and sanidine crystals record the remobilization of a cold crystal mush preceding the onset of effusive eruptions. This remobilization facilitated the formation of large amounts of phenocrysts, promoting outgassing and ultimately leading to the formation of a lava dome. In contrast, pumices produced during explosive eruptions are phenocryst-poor, devoid of microlites, and rich in vesicles, suggesting limited outgassing during these events. Notably, clinopyroxene phenocrysts exhibit homogeneous rim compositions (Mg# 73-77) throughout the eruptive sequence. Clinopyroxene--liquid thermometry yields pre-eruptive temperatures of 950-970°C for all the eruptions, indicating that this pre-eruptive parameter was not a primary factor controlling the transition between effusive and explosive events. Instead, pre- and syn-eruptive processes, such as crystallization, magma degassing, and outgassing, likely exerted a significant role in determining the eruptive style transitions.