Understanding the last 3600 years plumbing system evolution of Santorini volcano: contributions by in-situ micro-Sr isotope data

Petrogenetic processes such as magmas interaction and crustal contamination can be investigated by micro-Sr isotope analyses in minerals because the latter are able to retain the history of physical and chemical changing conditions during their growth. In this light micro-quantity analyses play a key role in the understanding of magmatic system. In particular, analyses of 87Sr/86Sr on core-rim traverses of minerals give us the chance to understand the dynamics and timescales of magmatic processes during the ascent of magma to the surface. We investigated the plumbing system evolution of the Santorini volcano (Greece) during the last 3.6 ky, after the occurring of the catastrophic, caldera-forming Minoan eruption. In particular, we focused our studies on dacitic lavas of the first and last post-caldera subaerial Kameni activity (46-47 A.D. and 1950 A.D., respectively), also comparing the obtained data with those analyzed in the previous Minoan volcanic products. Basaltic to andesitic magmatic enclaves are included in these lavas and Sr isotopes increase with time in both enclaves and host lavas. We have performed Sr and Nd isotope data of mafic enclaves and textural, compositional and micro-Sr isotope analyses of plagioclase crystals in post-caldera lavas. The isotope data on enclaves have contributed to better define the crustal contamination processes occurring in the mafic magmas feeding the silicic system. Micro-Sr isotopes on plagioclase, analyzed by microdrilling technique, agree with the previously proposed Kameni plumbing system (Conticelli et al. 1998; Francalanci et al. 1998; Petrone et al. 2013) represented by a zoned magma chamber where a resident dacitic magma interacts with small input of mafic magma by mixing and mingling processes. 87Sr/86Sr values of plagioclase do not largely change within the single eruptive event and generally reflect the respective whole-rock values, except for some xenocrysts in Kameni lavas coming from the mafic enclaves. Our data suggest that the Kameni plagioclases record a short history, indicating small resident time and possible crystallization during the magma ascent. Comparison with micro-Sr isotope data performed on plagioclases of Minoan pumices indicates this system has no relationships with the huge magma reservoir of the previous explosive Minoan activity.