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Magma storage, evolution and degassing at Mombacho (Nicaragua): new insights to decipher the current state of activity of a long dormant volcano

Manon Pouget1 , Séverine Moune1, David Chavarria2, Fausto Grassa3, Marta Ibarra2, Étienne Médard1, Federica Schiavi1, Cristhian Torrez2, Benjamin van Wyk de Vries1, Guillaume Boudoire^1 ^

  • Affiliations: 1Laboratoire Magmas et Volcans, Université Clermont-Auvergne, CNRS, IRD, OPGC, Clermont-Ferrand, France; 2Dirección General de Geología y Geofísica, Instituto Nicaragüense de Estudios Territoriales, Managua, Nicaragua; 3Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Palermo, Italia

  • Presentation type: Talk

  • Presentation time: Thursday 16:15 - 16:30, Room R380

  • Programme No: 1.8.3

  • Theme 1 > Session 8

Abstract

The Mombacho is a basaltic-andesitic stratovolcano of Nicaraguan Quaternary volcanic chain. As no eruption has been recorded at Mombacho, no information is available on the depth of potential magma storage zones, nor on the evolution of ascending magmatic fluids. However, this information is urgently needed given the current state of the volcano, which is showing signs of unrest. To acquire this knowledge, melt inclusions and pyroxene crystals in various Mombacho tephras were analysed, along with the volcanic gases emitted by crater fumaroles. The major element compositions of the melt inclusions support, to a first order, a magmatic evolution controlled by the fractional crystallisation of olivine, pyroxene, plagioclase and titanomagnetite crystals. However, the compositional variability of the most basic samples can only be explained by a source heterogeneity. Additional trace elements analyses agree with this hypothesis but seem to highlight a migration of the most mobile elements with an aqueous phase. The composition of the clinopyroxene crystals and the H2O and CO2 contents of the melt inclusions reveal the presence of a complex main storage zone between 0,75 and 2,5 kbar. Degassing modelling also supports this architecture and indicates that the gases sampled in 2024 in the Mombacho fumarole come from depths similar to this large storage zone. For their part, the 2024 fumarole temperature and gas composition are similar to those sampled during the last twenty years, highlighting the stability of the degassing and therefore of the underlying magmatic system.