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Protracted magma evolution associated with plutonic activity in the transcrustal magmatic plumbing system of the Erta Ale Volcano (Afar, Ethiopia)

Juliette Pin 1,2,3, Gilles Chazot1, Lydéric France2,4, Bénédicte Abily1, Andrey Gurenko2, Hervé Bertrand5, Alexandra Loppin1

  • Affiliations:  1 Laboratoire Geo-Ocean (LGO), Institut Universitaire Européen de la Mer (IUEM), Université de Bretagne Occidentale (UBO), Place Copernic, 29280 Plouzané, France; 2 Université de Lorraine, CNRS, CRPG, F-54000 Nancy, France; 3 Now at: University of Nevada, Reno, USA; 4 Institut Universitaire de France (IUF), France; 5 Laboratoire de Géologie de Lyon : Terre, Planètes, Environnement (LGL-TPE), Ecole normale supérieure de Lyon (ENS Lyon), 15 parvis René Descartes, 69342 Lyon, France 

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 209

  • Programme No: 1.9.16

  • Theme 1 > Session 9

Abstract

The Erta Ale Range rift system, located in Afar, includes six distinct volcanoes with lava compositions that range from basalts to rhyolites. However, only the Erta Ale Volcano (EAV) is currently active, where, until now, only basaltic compositions had been reported. We now report prolonged differentiation at EAV, which is not manifest volcanically at the surface but is instead accessible through unique cognate gabbroic and microgabbroic blocks. These samples reveal evolved parts of EAV's plumbing system that were previously undiscovered. We analyzed the major and trace element compositions of bulk rocks, interstitial glasses, and melt inclusions, and examined the oxygen isotopic compositions of olivine crystals. We combined these findings with textural data and oxy-thermo-barometry to discuss magma differentiation, storage conditions, and magmatic interactions. Our research, compared with rhyolite-MELTS thermodynamic models, confirms that prolonged fractional crystallization, associated with reactive porous flow, are the primary mechanism of magma evolution at EAV. These processes lead to the evolved compositions observed, reaching up to 75 wt.% SiO2. Oxygen isotopic analyses show substantial interactions with hydrothermally altered wall rocks. Finally, we also use the model outputs to quantify distinct phases of igneous differentiation in both shallow and deep crustal reservoirs, highlighting significant interactions and mixing between the different parts of the transcrustal plumbing system, particularly between the crystallizing plutons and dykes that accommodate the rift extension, and the ascending magma feeding the frequent eruptions.   Pin et al., 2024. Journal of Petrology 65, egae118. https://doi.org/10.1093/petrology/egae118