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, supply- ing 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 melt- and 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) disag- gregation 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.