Unravelling the magma feeding system of a young basaltic oceanic volcano

Zanon, V., Pimentel, A., Auxerre, M., Marchini, G. and Stuart, F. M. (2020) Unravelling the magma feeding system of a young basaltic oceanic volcano. Lithos, 352-35, 105325. (doi: 10.1016/j.lithos.2019.105325)

Abstract

A multidisciplinary approach combining petrological, geochemical, and fluid-inclusion studies with seismic monitoring data was used to build a model of the magma feeding system of Pico volcano (Azores islands, North Atlantic Ocean). We explore how magma has ascended to the surface in the last 10 ka and how this ascent is associated with the selective activation of the three tectonic systems intersecting the volcano. The deepest and most important ponding level for all ascending magmas is located at 17.3–17.7 km and corresponds to the Moho Transition Zone (MTZ), which marks the transition from mantle rocks to ultramafic cumulates. At shallower depth ascending magmas carry >30 vol% of clinopyroxene and olivine. Each magma ascent followed a distinct path and ponded often for a limited period. Ponding levels common to all feeding systems are present at 16.3–16.7 km, 12.1–14.5 km, 9.4–9.8 km, and 7.7–8.1 km. These depths mark important discontinuities where magmas formed stacked sills and evolved through fractional crystallisation. Dense and un-decrepitated fluid inclusions show rapid ascent from the MTZ along the Lomba do Fogo-São João fault (N150° system) and along the N120° regional transtensive system, despite multiple intrusions. Magma ponding at 5.6–6.8 km occurs where the N150° and N60° tectonic systems intersect each other. Here magma evolves towards plagioclase-rich and is only erupted at the summit crater and subterminal vents. This region is the source of the frequent microseismicity recorded at 4 to 7 km beneath the southern flank of Pico volcano, which might be associated with the early stages of formation of a more complex magma reservoir. The local and regional tectonics are of paramount importance in the activation of the different magma feeding systems over time. This new information is fundamental to improve the knowledge on the future eruptive behaviour of Pico volcano and can have significant implications on the mitigation of volcanic risk. This multidisciplinary approach can be applied not only to other volcanoes of the Azores but also to poorly monitored oceanic volcanoes, where magma ascent strongly depends on the activation of tectonic systems.

• Item Type: Articles
• Additional Information: The Portuguese Fundação para a Ciência e Tecnologia (FCT) through project MARES (PTDC/GEO-FIQ/1088/2014) supported the analytical work and grants of GM and MA. Free access to the summit of Pico volcano during field surveys in 2016, 2017 and 2018 has been provided by the Parque Natural do Pico. The Centro de Informação e Vigilância Sismovulcânica dos Açores (CIVISA) is acknowledged for providing the seismic data. Authors are grateful to the staff of the Centro de Aquisição de Dados of CIVISA and also to S. Oliveira for the help with the seismic database. A. Risplendente and S. Poli of the “Ardito Desio” University of Milan (Italy) are acknowledged for providing help during microprobe analyses.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Stuart, Professor Fin
• Authors: Zanon, V., Pimentel, A., Auxerre, M., Marchini, G., and Stuart, F. M.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Lithos
• Publisher: Elsevier
• ISSN: 0024-4937
• ISSN (Online): 1872-6143
• Published Online: 07 December 2019
• Copyright Holders: Copyright © 2019 Elsevier B.V.
• First Published: First published in Lithos 352-353:105325
• Publisher Policy: Reproduced in accordance with the publisher copyright policy