Combining textural and geochemical investigations to explore the dynamics of magma ascent during Plinian eruptions: a Somma–Vesuvius volcano (Italy) case study

Abstract

Trigger mechanisms and syn-eruptive processes of Plinian eruptions are poorly understood especially in the case of mafic powerful events. In the last decades, the combined geochemical and textural studies on volcanic rocks have proven to be fundamental tools for exploring the dynamics of magma ascent in volcanic conduits and for improving our ability to interpret volcano-monitoring signals and assess hazard. In this case study, we quantitatively investigate 2D and 3D micro-textural, geochemical, and isotopic features of pyroclastic rocks erupted during the Pomici di Base Plinian eruption (22 ka), the generally acknowledged first and most powerful event of the Somma–Vesuvius volcano. A peculiar aspect of this eruption is its high intensity that remained stable during the entire Plinian phase despite the strong magma compositional variation towards mafic terms. We infer that the transfer of magma towards the surface was intensified by the occurrence of rapid vesiculation pulses driven by limestone assimilation (skarn recycling) during magma ascent through the carbonatic bedrock. We conclude that limestone assimilation can hence be a syn-eruptive process, able to trigger further gas nucleation with deep impact on the eruption intensity, particularly crucial in the case of mafic/intermediate magma compositions.