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

Abstract

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.

The Medial Offshore Record of Explosive Volcanism Along the Central to Eastern Aegean Volcanic Arc: 2. Tephra Ages and Volumes, Eruption Magnitudes and Marine Sedimentation Rate Variations

“…This age is much younger than the Ar/Ar ages determined by Zhou et al. (2021), and is unambiguously constrained by the underlying 39.85 ka marine tephra of the Campanian Ignimbrite eruption. The discrepancy with the biotite‐dating results may be related to excess argon problems in biotite but may also mean that the onshore tephra dated by Zhou et al.…”

“…The discrepancy with the biotite‐dating results may be related to excess argon problems in biotite but may also mean that the onshore tephra dated by Zhou et al. (2021) is from an older eruption of the Firiplaka volcano that did not, however, leave a trace in the investigated cores.…”

“…The recognition that the Firiplaka Tephra from Milos is widespread demonstrates that plinian eruptions have occurred that were much more powerful than the phreatomagmatic eruptions hitherto recognized on land, and that explosive volcanism on Milos is significantly younger (36.3 ka) than previously thought (>62 ka; Zhou et al., 2021).…”

“…The 37.0 ± 1.3 ka age of the Firiplaka Tephra has important implications for volcanic hazard assessment at Milos because it shows that highly explosive volcanism extended to much younger times than those suggested by radiometric dating (>60 ka; Zhou et al., 2021), in addition to showing that plinian eruptions have occurred that have not yet been recognized in the onshore stratigraphy.…”

“…In all cores, the marine tephra lies above ash layers from the 39.85 ka Campanian ignimbrite eruption (Giaccio et al., 2017), and below ash layers correlated with the 27.5 ka Cape Tripiti (Satow et al., 2015) or the 22 ka Cape Riva eruptions (Bronk Ramsey, Albert, et al., 2015). Recent Ar/Ar age dating of biotites from Milos suggested an age of 317 ± 4 ka for the Trachilas complex, an older pyroclastic sequence from Milos (Fytikas et al., 1986), and ages of 62 ± 3 ka, 70 ± 10 ka and 110 ± 20 ka for biotites from the upper and lower Firiplaka tephra sequence in the south of Milos (Zhou et al., 2021).…”