Boudoire G, Rizzo A L, Arienzo I, Di Muro A
Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, 6 avenue Blaise Pascal, 63178, Aubière, France.
Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo La Malfa 153, 90146, Palermo, Italy.
Sci Rep. 2020 Jun 17;10(1):9809. doi: 10.1038/s41598-020-66260-x.
Helium (He) with its isotopes (He, He) is a key tracer enabling the Earth's mantle and dynamics to be characterized. Enrichment in primordial helium (He) has been detected in volcanic gases of numerous magmatic systems in different geodynamic settings. Despite past use to monitor volcano-tectonic unrest, temporal He/He 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 He/He in response to the eruptive activity have never been studied. We compare the He/He signature of volcanic gases and fluid inclusions and we highlight analogous evolution of the He/He signature in both during the last decades of eruptive activity (1990-2017), even during the same eruption. We show that the maximum enrichment in He is found in magmatic fluids that fed the most voluminous eruptions which culminated in caldera collapse events. We argue that this enrichment in He 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).
氦（He）及其同位素（He、He）是一种关键示踪剂，可用于表征地球地幔及其动力学特征。在不同地球动力学环境下的众多岩浆系统的火山气体中，已检测到原始氦（He）的富集现象。尽管过去曾利用它来监测火山 - 构造活动的不稳定情况，但火山喷发物中He/He随时间的变化情况仍受到的限制较少。在此，我们研究了富尔奈斯峰热点火山的稀有气体化学性质，此前从未对其He/He随喷发活动的时间波动情况进行过研究。我们比较了火山气体和流体包裹体的He/He特征，并强调了在过去几十年的喷发活动（1990 - 2017年）期间，甚至在同一喷发过程中，两者的He/He特征具有相似的演化过程。我们发现，在为最大规模喷发提供物质的岩浆流体中，He的富集程度最高，这些喷发最终导致了破火山口坍塌事件。我们认为，He的这种富集主要反映了来自地幔柱原始组分的岩浆流体的更大贡献。这些结果强调，He同位素可能会为深部岩浆贡献增加提供预警，而深部岩浆贡献增加可能预示着阵发性喷发，正如在此记录的富尔奈斯峰（2007年）以及基拉韦厄火山（2018年）的情况。
