Investigating the deepest part of a volcano plumbing system: Evidence for an active magma path below the western flank of Piton de la Fournaise (La Réunion Island)

Guillaume Boudoire 1, 2 Marco Liuzzo 3 Andrea Di Muro 2 Valérie Ferrazzini 2 Laurent Michon 1 Fabio Grassa 3 Allan Derrien 2 Nicolas Villeneuve 2 A Bourdeu 4 Christophe Brunet 2 Gaetano Guidice 3 S Gurrieri 3
1 LGSR - Laboratoire GéoSciences Réunion
2 OVPF - Observatoire Volcanologique du Piton de la Fournaise
3 Istituto Nazionale di Geofisica e Vulcanologia
4 EOST - Ecole et Observatoire des Sciences de la Terre
Abstract : Peripheral diffuse degassing of CO2 from the soil occurs across the western flank of Piton de la Fournaise volcano (La Réunion Island, Indian Ocean) along a narrow zone. In this area, carbon isotopic analysis on soil gas samples highlights significant mixing between magmatic and organic end-members. The zones with the strongest mag- matic signature (highest δ13C) overlap spatial distribution of hypocenters recorded shortly before and during vol- cano reactivation and allow discriminating a N135° degassing lineament, with a minimum length of 11 km and 140 ± 20 m-width. Such orientation is in accordance with that of an old dyke network along the rift zone and with N120–130° and N140–155° lineaments related to the inheritance of oceanic lithosphere structures. Our findings show that this N135° lineament represents a preferential magmatic pathway for deep magma transfer below the volcano flank. Moreover, spatial distributions of recent eccentric cones indicate a well-founded possibil- ity that future eruptions may by-pass the shallow plumbing system of the central area of the volcano, taking a lat- eral pathway along this structure. Our results also confirm that Piton de la Fournaise activity is linked to a laterally shifted plumbing system and represent a major improvement in identifying the main high-risk area on the densely populated western flank of the volcano.
Keywords : Soil CO2 emissions δ13C - isotope tracers magma migration photogrammetry seismicity
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Guillaume Boudoire, Marco Liuzzo, Andrea Di Muro, Valérie Ferrazzini, Laurent Michon, et al.. Investigating the deepest part of a volcano plumbing system: Evidence for an active magma path below the western flank of Piton de la Fournaise (La Réunion Island). Journal of Volcanology and Geothermal Research, Elsevier, 2017, 341, pp.193-207. ⟨10.1016/j.jvolgeores.2017.05.026⟩. ⟨hal-01565713⟩

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