The February-March 2021 lava fountains events of Mt. Etna South-East crater: insights from clinopyroxenes. 

Abstract

Mt. Etna is the most active volcano in Europe with four active vents in the summit area. The South-East Crater (SEC) is the most active crater of the last 20 years and is characterised by episodic eruptions, i.e. sequences of paroxysmal lava fountains with rather variable frequency and duration from a few weeks to months. Between December 2020 and February 2022, the SEC produced over 60 paroxysmal events divided into a first phase (December 2020 – April 2021) and a second phase (May 2021 - February 2022). We investigated textural and chemical characteristics of the clinopyroxenes population to constrain frequency of magma recharge episodes and eruption triggering mechanisms of 6 paroxysms representative of the first phase, from February 16 to March 10 2021, including the February 28 paroxysm which erupted the most primitive magma.  Clinopyroxenes show frequent sector zoning superimposed on complex concentric zoning showing two main compositional domains: 1) augitic composition (Mg# 68-75) which mostly characterises rims and is less frequent in cores and mantles; 2) diopsidic composition (Mg# 74-80) mainly found in cores and less abundant in mantle and rims. Barometric estimates using the new GAIA deep learning-based thermobarometry (Chicchi et al., 2022 EPSL) indicate a shallow reservoir (0.4-1.0 ± 0.3 kbar) for the augitic domain and a deeper reservoir (1.7-2.7 ± 0.5 kbar) for the diopsidic domain. Fe-Mg diffusion timescales point to the occurrence of multiple episodes of mafic recharges starting in December 2020 and up to a few days prior eruption in agreement with monitoring data.