Rift zones and magma plumbing system of Piton de la Fournaise volcano: How do they differ from Hawaii and Etna?

Abstract

International audienceOn ocean basaltic volcanoes, magma transfer to the surface proceeds by subvertical ascent from the mantle lithosphere through the oceanic crust and the volcanic edifice, possibly followed by lateral propagation along rift zones. We use a 19-year-long database of volcano-tectonic seismic events together with detailed mapping of the cinder cones and eruptive fissures to determine the geometry and the dynamics of the magma paths intersecting the edifice of Piton de la Fournaise volcano. We show that the overall plumbing system, from about 30 km depth to the surface, is composed of two structural levels that feed distinct types of rift zones. The deep plumbing system is rooted between Piton des Neiges and Piton de la Fournaise volcanoes and has a N30–40 orientation. Above 20 km below sea level (bsl), the main axis switches to a N120 orientation, which permits magma transfer from the lithospheric mantle to the base of the oceanic crust, below the summit of Piton de la Fournaise. The related NW-SE rift zone is 15 km wide, linear, spotted by small to large pyroclastic cones and related lava flows and emits slightly alkaline magmas resulting from high-pressure fractionation of clinopyroxene ± olivine. This rift zone has low magma production rate of ~ 0.5–3.6 × 10 −3 m 3 s −1 and an eruption periodicity of around 200 years over the last 30 ka. Seismic data suggest that the long-lasting activity of this rift zone result from regional NNE-SSW extension, which reactivates inherited lithospheric faults by the effect of underplating and/or thermal erosion of the mantle lithosphere. The shallow plumbing system (b11 km bsl) connects the base of the crust with the Central Cone. It is separated from the deep plumbing system by a relatively large aseismic zone between 8 and 11 km bsl, which may represent a deep storage level of magma. The shallow plumbing system feeds frequent, short-lived summit and flank (NE and SE flanks) eruptions along summit and outer rift zones, respectively. Summit rift zones are very active (~0.1–0.25 m 3 s −1), short (2–3 km), and present an orthogonal pattern confined to the central active cone of Piton de la Fournaise. Outer NE and SE rift zones are much less active (~4–7.3 × 10 −3 m 3 s −1) and extend from inside the Enclos Fouqué caldera to bound the mobile eastern volcano flank. We show that the outer rift zones are almost aseismic and are genetically linked to the seaward flank displacements, whose most recent events where detected in 2004 and 2007. East flank sliding is itself triggered by shallow (b 2 km depth) sill intrusions. We propose that the subvertical magma intrusions along the perpendicular summit rift zones, sill intrusions, and subsequent magma injections along the outer rift zones are controlled by cycles of stress permutations. We thus tentatively propose that as for Piton de la Fournaise, the regional stress field acting on Etna and Hawaiian volcanoes is an important parameter in the control of the magma transfer along their deep plumbing system whereas the dyna...

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)

“…1; Bachèlery, 1981;Chevallier and Bachèlery, 1981;Villeneuve and Bachèlery, 2006;Bonali et al, 2011;Liuzzo et al, 2015;Michon et al, 2015Michon et al, , 2016. The two most active of these are the SE and NE rift zones (SERZ and NERZ), which have been interpreted as shallow lateral pathways of magma initially injected below the central area.…”

“…In these sectors, recent flank eruptions have occurred every 50 years on average (Morandi et al, 2016) and have generally begun inside the Enclos Fouqué before lateral shallow magma migration (Villeneuve and Bachèlery, 2006). The SERZ and NERZ are thought to be closely linked to the central shallow plumbing system of Piton de la Fournaise and to result from the seawards displacement of the steep eastern flank (Bonali et al, 2011;Michon et al, 2015 ). On the aseismic SERZ and NERZ, Liuzzo et al (2015) have reported high soil CO 2 emissions, possibly defining a secondary deep magma transfer especially along recently active zones or/and possible tectonic structures oriented N90° cutting the western flank.…”

“…The third and largest rift zone, the NWRZ, has been characterised by peripheral eruptions for at least 29 ky (McDougall, 1971; Liuzzo et al, 2015;Michon et al, 2015). Seismicity shallower than 11 km (bsl) mainly occurs below the central cone (Enclos Fouqué) and is related to the shallow plumbing system of Piton de la Fournaise.…”

“…The parallelism between these features and the main regional tectonic structures (transform faults and paleo-ridge axes) has been interpreted as evidence of a control of the structural inheritance of the oceanic lithosphere in the magma migration . In this study, we focus on the seismic and volcanically active NW rift zone (NWRZ) on the western flank of Piton de la Fournaise, which has been interpreted as a sector of deep magma storage and potential lateral migration of magma towards the central and shallower plumbing system (Lénat et al, 2012Michon et al, 2015). The NWRZ is a 10-15-km-wide and 15-kmlong area displaying about 200 eruptive cones, some of which of recent (historical) age (Morandi et al, 2016).…”

First results of the Piton de la Fournaise STRAP 2015 experiment: multidisciplinary tracking of a volcanic gas and aerosol plume

“…About 97 % of the recent eruptive activity occurred in the 5465-2971-year-old Enclos Fouqué caldera ( Fig. 1), an approximately 8.5 × 13 km 2 -wide structure, which is an uninhabited seaward open natural depression (Villeneuve and Bachèlery, 2006;Michon et al, 2015;Ort et al, 2016). This intracaldera activity has contributed to the formation of the 400 m high summit cone with a top consisting of two depressions, the Dolomieu caldeira and the Bory crater, to the east and west respectively.…”