Magma mixing at Lipari (Aeolian Islands, Italy): Insights from textural and compositional features of phenocrysts

Abstract

In southern Lipari (Aeolian Islands, Italy) the volcanic activity was exclusively rhyolitic in the last 42 ka, but the presence of mafic magmas in the magmatic system is revealed by the occurrence of mingling and mixing textures in the silicic deposits. The study of textural and compositional zoning of phenocrysts is a powerful tool to unravel magmatic processes, especially when bulk rock data are affected by magma mixing. In this work we present the results of detailed petrographic and microanalytical investigations carried out on the rhyolitic products and their mafic enclaves, with the aim to improve the knowledge of the Lipari magmatic system in recent times. Trace element profiles on phenocrysts were carried out by Laser Ablation ICP-MS on the products of eruptions occurred around 22 ka ago. Mineral chemistry indicated the formation of different mafic magma batches in that period. Zoning patterns in clinopyroxene and plagioclase phenocrysts in enclaves record mixing between two different mafic magmas. This event preceded of less than a few years the syn-eruptive mixing with the rhyolite. Short residence times (less than hundreds of years) of plagioclase phenocrysts in the mafic magma prior to mixing with the rhyolite were calculated based on measured Sr profiles and diffusion kinetics. The results evidence the existence in southern Lipari of a composite, vertically developed magmatic system, storing silicic and mafic magmas as relatively small-volume batches interacting with each other.