Time scales of open-system processes in a complex and heterogeneous mush-dominated plumbing system

The architecture of a mush-dominated plumbing system in active volcanic areas conditions the magma pathways feeding eruptions. Open-system processes along these pathways and the associated time scales are directly related to monitoring data and eruptive behavior. Despite crystal mush-dominated systems being common in active volcanoes, previous studies have not focused on the integration of data from the mush sectors feeding different eruptions, supplying a partial view of the pre-eruptive magmatic processes and hindering the interpretation of the monitoring signals during unrest periods. We focus on the Marsili seamount (Tyrrhenian Sea), where the mineral data document processes within a magmatic system vertically extended throughout the local oceanic crust and made of a mush framework spotted with eruptible meltand crystal-rich pockets. We undertook a study of Marsili olivine crystals that constrains the time scales of three pre-eruptive scenarios, dominated by open-system processes: (1) disaggregation of the deep Marsili volcano mush zone that occurred over a time scale of years prior to the eruption; (2) rapid ascent (days) of mantle-derived basaltic magma that, in some cases, intercepts shallow plagioclase-rich pockets; and (3) multiple mixing events between melt- and crystal-rich mush zones occurring approximately 1-2 mo and 0.5-3 yr before the eruption. Our results highlight the importance of contemporaneously studying eruptions in different locations on a volcano edifice for a better comprehension on how mush-dominated plumbing systems work as a whole and how this must be considered during the interpretation of monitoring data.