Following the tracers of magma mixing; mafic enclaves within volcanic rocks at the Methana peninsula

Abstract

The presence of mafic enclaves within volcanic rocks, which present an evolved geochemical character, tends to be related to magma mixing. In the Hellenic Volcanic Arc, mafic enclaves are regularly encountered within the volcanics. There are a few reports regarding the islands of Santorini and Nisyros as well as in the peninsula of Methana. The petrographic and mineral chemistry data we present here concern enclaves only from the Methana peninsula. Enclaves in Methana vary in size (from a few cm up to hand-sized samples) and color (reddish to black) depending on their host lava. The typical mineral assemblage is amphibole + clinopyroxene + olivine + plagioclase ± spinel ± mica. Mineral phases of amphibole, olivine, and clinopyroxene form the major phenocrysts that are embedded within a matrix mostly of fine-grained plagioclase laths and fine-grained needle-shaped amphibole. Textural features of plagioclase reveal the predominance of wet conditions during their crystallization since their cores and/or intermediate growth zones are usually dissolved suggesting a hydrous and volatile enriched magma related to the mafic enclaves. The aforementioned mineral assemblage along with the latter petrographic features match with lamprophyric rocks and their typical porphyritic and panidiomorphic textures. This counterpart is further ascertained by the mineral chemistry of Mg-rich amphibole varieties, and primary forsterite-rich olivine as well as by the lamprophyre-related trends of clinopyroxene and mica. These preliminary results provide new insights regarding magma mixing processes that occurred at the western margin of the Hellenic Subduction Zone. Acknowledgments This work is part of the first author's Ph.D. research, which is financially supported by the «Andreas Mentzelopoulos Foundation».