HR: 08:45h
AN: V41F-04    [Abstracts]
TI: Constraints on the Rates of Replenishment, Magma Mixing, and Crystal Recycling at Santorini Volcano, Greece
AU: * Martin, V M
EM: victoria.martin@durham.ac.uk
AF: Durham University, Dept of Earth Sciences South Road, Durham, DH1 3LE, United Kingdom
AU: Davidson, J P
EM: j.p.davidson@durham.ac.uk
AF: Durham University, Dept of Earth Sciences South Road, Durham, DH1 3LE, United Kingdom
AU: Morgan, D J
EM: d.morgan@See.leeds.ac.uk
AF: University of Leeds, Earth Sciences School of Earth and Environment, Leeds, LS2 9JT, United Kingdom
AU: Jerram, D A
EM: d.a.jerram@durham.ac.uk
AF: Durham University, Dept of Earth Sciences South Road, Durham, DH1 3LE, United Kingdom
AB: Santorini is a young, active volcano, which preserves abundant evidence for open-system processes such as magma replenishment and crystal recycling, and thus represents an ideal system in which to study magma chamber dynamics. Santorini is the largest volcanic centre in the Aegean arc, with an eruptive history spanning more than 250,000 years over two eruptive cycles. The cycles are dominated by extended periods of effusive shield-building activity with occasional large-magnitude explosive eruptions, the Minoan eruption of ~3600 years ago being the most recent. Current activity consists of a phase of post-caldera reconstruction, focused recently on the intra-caldera Kameni islands. Microsampling to measure ⁸⁷Sr/⁸⁶Sr ratios of plagioclase cores indicates the presence of a complex plumbing system beneath Santorini. Large rhyodacitic deposits typically contain a mafic component, interpreted as the eruption trigger. In some cases, the mafic magma groundmass and phenocrysts are isotopically similar to their rhyodacite host; other deposits show the opposite, implying the coexistence of isotopically distinct magma batches. To add further complexity, plagioclase phenocrysts are in some cases in equilibrium with their groundmass while others show the reverse, implying modification due to crystal recycling or shallow mixing processes prior to eruption. Mafic enclaves in the recent Kameni lavas, again interpreted as the probable eruption trigger, provide some constraints on the rates of these recycling, mixing, and triggering processes. Glomerocrysts and xenocrysts of recycled gabbroic cumulate material are present in a number of Kameni enclaves. Isotopic and chemical disequilibrium between the cumulate crystals and the host indicate that these fragments are derived from pre- existing crystal mush piles pervaded by the replenishing melts as they migrated to shallow levels, creating disequilibrium between the cumulate mineral cores and the replenishing melts. ⁸⁷Sr/⁸⁶Sr isotope ratios of plagioclase xenocryst cores suggest crystal recycling from a pre-Minoan source is probable. Olivine xenocrysts in the enclaves possess narrow (10-30 μm) Fe-Mg diffusion profiles, due to interaction with enclave magma groundmass, which can be used to estimate the interval between entrainment and eruption. Initial modelling of diffusion profiles from more than 60 crystals suggests short timescales, from 15 to 45 days, for the combined migration-replenishment-eruption cycle at Kameni.
DE: 1036 Magma chamber processes (3618)
DE: 1040 Radiogenic isotope geochemistry
DE: 1042 Mineral and crystal chemistry (3620)
DE: 3625 Petrography, microstructures, and textures
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting