Rapid accumulation and ascent precedes caldera forming eruption of low viscosity magma

Abstract

Mafic magma is commonly associated with effusive eruptions, however several mafic volcanoes throughout the globe have produced explosive eruptions. Here we present one such volcano – Colli Albani. Colli Albani is 20 km SE of Rome and produced seven large volume ignimbrites. Field observations, mineral chemistry, and Sr and Nd isotopes in clinopyroxene show that the high potassic, silica undersaturated and CO$$_{2}$$ 2 -rich magma typical of Colli Albani is produced by partial melting of a metasomatized mantle. Clinopyroxene based thermobarometry combined with thermal modelling, indicates rapid accumulation of magma into the shallow crust preceding the last caldera forming event (355 ka). The crystallization of high Mg# and high Cr$$_{2}$$ 2 O$$_{3}$$ 3 clinopyroxenes at low pressures and high temperatures indicates rapid magma ascent from the mantle. We suggest that a final rapid input of this deeply sourced magma destabilised the shallow and fast assembled magma reservoir and lead to the caldera forming event. Our findings have significant implications for the evaluation of the timescales of reactivation of Colli Albani and other similar long-quiescent calderas erupting low viscosity magmas, as rapid migration of magma to shallow reservoirs may result in short unrest periods prior to a large eruption.

A new calibration of the OPAM thermobarometer for anhydrous and hydrous mafic systems

“…Irrespective of the calibration strategy, thermobarometers have significant scope as petrological volcano monitoring tools. For example, P data can independently validate geophysical estimates of pre-eruptive magma storage depth during or after eruptions (Hartley et al, 2018;Stock et al, 2018;Ubide et al, 2023) or catalogue past changes in magma P and T for eruptions of volcanoes that lack a protracted historical monitoring record (Bouvet de Maisonneuve et al, 2021;Higgins et al, 2021a;Jorgenson et al, 2024;Weber et al, 2020).…”