Garnet Xenoliths in Andesitic Lavas of Lipari: New Geochemical Data to Provide Additional Information on the Metamorphic Basement Under the Aeolian Arc

Abstract

The purpose of this paper is to discuss and interpret a comprehensive set of geochemical (major and trace elements) data for xenolithic garnets included in high-K andesites from Lipari Island (Aeolian Archipelago, Italy), with the aim to constraint the parent rocks. Since, among all the mineral phases, garnet has a high affinity for the heavy REE (Dy-Lu) and HFSE (Hf, Zr, Ti), we use it as petrogenetic indicator. The investigated xenoliths are mainly composed of cordierite, garnet and Al-silicates and are considered as fragments of the metamorphic Calabria-Peloritani Orogen inferred to be the basement beneath the Aeolian volcanoes. Xenolithic garnet from Lipari andesites and metamorphic garnets from rocks of Southern Calabria and Peloritani Mountains were sampled and analysed. Major elements were determined through ESEM, whereas trace elements were acquired using LA-ICP-MS. Two types of garnets were recognised on the base of major elements, one homogeneous and one zoned, whit an almandine-dominant composition. The comparison between major and trace elements data of xenolithic and metamorphic garnets allowed defining nature of the basement beneath Lipari Island, which is composed of: a) a metamorphic Unit similar to the kinzigitic ones for the unzoned crystals; b) a metamorphic unit similar to the Aspromonte and not outcropping in Sicily and in Calabria for the zoned garnets.