Spatial and temporal mush heterogeneity during eruptions recorded in clinopyroxene from the 2021 paroxysms at Mt. Etna, Italy

Textural and compositional zoning of volcanic minerals archives pre-eruptive magma processes. Crystals erupted simultaneously may be sampled from different regions of the plumbing system and hence record variable histories due to complex magma dynamics. In addition, crystals erupted throughout the course of an eruption may record temporal variations in the plumbing system. To resolve mush variability on both spatial and temporal scales, we investigate clinopyroxene erupted during a series of paroxysmal episodes between February–April 2021 at Mt. Etna, Italy. Using a combination of high-resolution geochemical techniques, we observe that Cr enrichments in clinopyroxene mantle zones, grown upon eruption-triggering mafic rejuvenation, exhibit both temporal and spatial (sample-scale) variability. Temporal variability correlates with changes in glass compositions, attesting to the ability of clinopyroxene to track magma maficity throughout an eruption. Spatial variability, indicated by the scatter of Cr concentrations, is greatest for the first event and lowest for the final paroxysm. In conjunction with core textures, degree of sector enrichment and thermobarometry, our data suggest that the onset of the paroxysms was preceded by the remobilisation of a mid-crustal clinopyroxene mush (534±46 MPa) by hot, mafic magma causing variable resorption of mush-derived crystal cores. Towards the end of the eruption, waning magma supply led to less efficient mush remobolisation and mixing, resulting in homogenous crystal populations. Our results highlight that clinopyroxene Cr contents and sector enrichment can be used to track mafic rejuvenation and magma evolution throughout eruptions, while also reflecting spatial heterogeneities within the plumbing system.