Short crystal history in the recent magmatic system of Santorini volcano, Greece: inferences from micro-Sr isotope data

Magma mineral phases retain the history of changing physical and chemical conditions during their growth due to the frequent occurring of mineral/liquid elemental and isotopic disequilibria. In many volcanic systems, indeed, bulk rock compositions often represent a mechanical mixture of various phases with possible different origin. Accordingly, 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. Micro-Sr isotope analyses, by microdrilling, have been used, therefore, for better understanding the volcanic system of the last 3.6 ka of Santorini history, from the huge explosive event of the Minoan eruption to the successive Kameni activity. The latter originated the Palea- and Nea-Kameni islets, inside the Minoan caldera, through nine mainly effusive subaerial events, from A.D. 46-47 to 1950. The erupted products are dacitic lavas including basaltic to andesitic enclaves, with Sr isotopes increasing with time in both enclaves and host lavas. www.minersoc.org DOI: 10.1180/minmag.2013.077.5.4 We focussed our micro-analytical study on the plagioclase crystals of the rhyodacitic pumices from the Minoan eruption and of the oldest and youngest post-caldera dacitic lavas. Different types of plagioclase have been identified based on textures and zoning patterns. Anorthite content overall varies between 35-90% in both systems. Contrarily to many other volcanic systems, 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. The different crystal types of the Minoan pumices have similar 87Sr/86Sr values, which are higher than those of the Kameni plagioclases. Our data suggest that the Kameni plagioclases record a short history, indicating small resident time and possible crystallization during the magma ascent, whereas the Minoan crystals do not testify any relationships with both the coeval mafic magmas and the later Kameni system.