Eruptive history and 40Ar/39Ar geochronology of the Milos volcanic field, Greece

Abstract. High-resolution geochronology is essential to determine the growth-rate of volcanoes, which is one of the key factors to establish the periodicity of explosive volcanic eruptions. However, there are less high-resolution eruptive histories (> 106 years) determined for long-lived submarine arc volcanic complexes than for subaerial complexes, since the submarine volcanoes are far more difficult to observe than subaerial ones. In this study, high-resolution geochronology and major element data are presented for Milos Volcanic Field (VF) in the South Aegean Volcanic Arc, Greece. The Milos VF has been active for over 3 Myrs, and the first two million years of its eruptive history occurred in a submarine setting that has emerged above sea level nowadays. The long submarine volcanic history of the Milos VF makes it an excellent natural laboratory to study the growth-rate of a long-lived submarine arc volcanic complex. This study reports twenty-one new high-precision 40Ar/39Ar ages and major element compositions for eleven volcanic units of the Milos VF. This allows us to refine the volcanic evolution of Milos into nine phases and five volcanic quiescence periods of longer than 200 kyrs, on the basis of age, composition, volcano type and location. Phase 1–5 (~ 3.34–1.60 Ma) contributed ~ 85 % by volume to the Milos VF, whereas the volcanoes of Phase 6–9 only erupted small volumes (2–6 km3 in DRE) rhyolitic magmas. Although there are exceptions of the felsic cone volcanoes of Phase 1–2, in general the Milos VF becomes more rhyolitic in composition from Phase 1 to Phase 9. In particular, the last three phases (Phase 7–9) only contain rhyolites. Moreover, the high-resolution geochronology suggests that there are at least three periods of different long term volumetric volcanic output rate (Qe). In the Milos VF, the Qe varies between 0.2 and 6.6 × 10−5 km3 yr−1, 2–3 orders of magnitude lower than the average for rhyolitic systems and continental arcs.