Unravelling the magma feeding system of a young basaltic oceanic volcano

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 *Revised Manuscript with No changes marked Click here to download Revised Manuscript with No changes marked: Pico#1 Manuscript -final 1.0_AP.docx 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.

Upper Mantle Mush Zones beneath Low Melt Flux Ocean Island Volcanoes: Insights from Isla Floreana, Galápagos

“…of the crust (Longpre et al, 2014;Taracsák et al, 2019;Zanon et al, 2020). Hence, we speculate that the flux of magma from the underlying mantle source has a first-order control on the depth of magma storage beneath ocean island volcanoes and, correspondingly, high-pressure magma storageas observed beneath Floreanais characteristic of low melt flux ocean island volcanoes globally.…”

“…Our results have global implications for the architecture and dynamics of magma storage regions beneath ocean island volcanoes worldwide. The observed difference in magma storage depths beneath high and low melt flux volcanic systems in the Galapagos Archipelago is mirrored in a global compilation of barometric data from ocean island volcanoes (Famin et al, 2009;Geist et al, 1998;Hammer et al, 2016;Hartley et al, 2018;Klügel et al, 2015;Poland et al, 2015;Stock et al, 2018;Zanon et al, 2020;Zanon and Pimentel, 2015). Using the average repose period between eruptions at a particular basaltic volcanic centre as a proxy for the flux of magma entering the lithosphere from the underlying mantle (Global Volcanism Program, 2013), Figure 14 shows that the most frequently active volcanic centres (such as, Kīlauea, Hawai'i, and Piton de la Fournaise, Réunion) are characterised by persistent magma storage in the mid to upper crust (Famin et al, 2009;Poland et al, 2015).…”

“…A general trend to greater magma storage pressures is observed with increasing repose period, indicating that the flux of magma from the mantle has a first order control on the depth of magma storage. Data from (Famin et al, 2009;Geist et al, 1998;Hammer et al, 2016;Hartley et al, 2018;Klügel et al, 2015;Poland et al, 2015;Stock et al, 2018;Zanon et al, 2020;Zanon and Pimentel, 2015).…”

Magma water content of Pico Volcano (Azores Islands, Portugal): a clinopyroxene perspective

“…In detail, we selected basalts representing primitive compositions erupted by the lateral activity of Pico Volcano from less than 40 ka to AD 1718 ( Fig. 1) characterised by Zanon and Frezzotti (2013), Métrich et al (2014) and Zanon et al (2020). We measured hydrogen content, geobarometric data, and iron oxidation state at the core of clinopyroxenes extracted from the selected basalts to estimate the water content of the primitive parental melt in equilibrium with the clinopyroxene cores and reconstruct their crystallisation pressure.…”

Highs, Lows, and Puzzling Intensity Variations of the Earth’s Magnetic Field

“…is the youngest volcano of the archipelago (53 ± 5 ka; Costa et al, 2014) and constitutes the western part of the island. This central volcano is characterized by gentle lower slopes punctuated by numerous scoria cones at its base, while it rises up to 2351 m as a conical shape edifice with steep slopes towards the top (Nunes, 1999;Nunes, 2020;Zanon et al, 2020). The geological record of Pico Island reveals a high eruptive frequently during the Holocene.…”