Abstract
Helium (He) with its isotopes (3He, 4He) is a key tracer enabling the Earth’s mantle and dynamics to be characterized. Enrichment in primordial helium (3He) has been detected in volcanic gases of numerous magmatic systems in different geodynamic settings. Despite past use to monitor volcano-tectonic unrest, temporal 3He/4He variability in volcanic emissions is still poorly constrained. Here, we investigate noble gas chemistry of Piton de la Fournaise hotspot volcano, where temporal fluctuations of 3He/4He in response to the eruptive activity have never been studied. We compare the 3He/4He signature of volcanic gases and fluid inclusions and we highlight analogous evolution of the 3He/4He signature in both during the last decades of eruptive activity (1990–2017), even during the same eruption. We show that the maximum enrichment in 3He is found in magmatic fluids that fed the most voluminous eruptions which culminated in caldera collapse events. We argue that this enrichment in 3He mostly reflects a greater contribution of magmatic fluids from a primitive component of the mantle plume. These results emphasize that He isotopes may provide warnings of increases in deep magmatic contributions that potentially herald paroxysmal eruptions, as documented here at Piton de la Fournaise (2007) and also at Kilauea (2018).
Highlights
Helium (He) with its isotopes (3He, 4He) is a key tracer enabling the Earth’s mantle and dynamics to be characterized
We aim to compare He systematics in fluid inclusions (FI) in crystals from lavas and cumulates (Table S1) of Piton de la Fournaise (PdF) with (i) Sr isotopes of host rocks/crystals (Table S1) and (ii) He isotopes in volcanic gases from thermal springs (Table S2) from Piton des Neiges (PdN)
Through the study of the 3He/4He signature of volcanic gases and fluid inclusions at La Réunion island, we infer that a predominant contribution (>95%) of a primitive component of the mantle plume leads to the production and ascent of melts and magmatic fluids (Rc/Ra >13.7) responsible for unusual “paroxysmal” eruptions, as observed for the most recent caldera collapse eruptions at Piton de la Fournaise (PdF) (Fig. 7)
Summary
Helium (He) with its isotopes (3He, 4He) is a key tracer enabling the Earth’s mantle and dynamics to be characterized. With the exception of a few intra-plate volcanoes on Earth (e.g., Etna, El Hierro), most of the studies of 3He/4He monitoring volcanic gases have been carried out in subduction-related settings (e.g., Stromboli, Santorini, Turrialba, Ontake) where long quiescent periods and/or the emission of variably differentiated lavas, often free of gas-rich fluid inclusions in mafic minerals, are common[18,20,21,22,23] This makes comparing 3He/4He in volcanic gases and FI challenging at active volcanoes, even if it could potentially shed light on the ongoing magmatic dynamics as well as on magma www.nature.com/scientificreports residence and crystallization timing and allow the forecasting of unrest phases.
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