U-Th zircon dating reveals a correlation between eruptive styles and repose periods at the Nisyros-Yali volcanic area, Greece

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

“…The reason for this discrepancy requires further investigation. We note that in core POS513-52 the compositionally correlated N1 tephra, which was dated on land by Popa et al (2020) between ∼55 and ∼60 ka, is located only 5 cm below the Yali-1 tephra. If the ∼40 ka age from Popa et al ( 2020) is correct, this sediment interval would have been emplaced at a very low sedimentation rate (0.25-0.33 cm/kyr) whereas our Yali-1 age would give a rate (0.9-10 cm/kyr), which is more compatible with the regional sedimentation-rate values (Figure 3).…”

“…Until recently the age of the Yali-1 pumice breccia (Allen & McPhie, 2000) could not be constrained because the base of the proximal deposit on land and underlying strata are not exposed, and so far radiometric ages had not been obtained. However, Popa et al (2020) obtained zircon ages of 37.8 ± 9.5 to 41.3 ± 6.8 ka for Yali-1.…”

“…Specifically, published ages for the Lower Pumice from Nisyros (>70 ka to ∼29 ka) are incompatible with those for the Upper Pumice (>50 ka to 35 ka) (Karkanas et al, 2015;Limburg & Varekamp, 1991;Margari et al, 2007;Rehren, 1988;Tomlinson et al, 2012). Popa et al (2020) recently published zircon crystallization ages of 54.9 ± 10.5 ka to 60.4 ± 3.9 ka for the Upper Pumice and 59.9 ± 17.1 ka to 74.3 ± 5.5 ka for the Lower Pumice; these ages overlap within the given error limits. As a result, the age of a major sector collapse event on Nisyros has not yet been well constrained (Anagnostopoulos & Anastasakis, 2021;Livanos et al, 2013;Tibaldi et al, 2008) and event frequencies used in volcanic hazard assessment remain uncertain (e.g., Kinvig et al, 2010;Nomikou et al, 2021;Seymour & Vlassopoulos, 1989).…”

“…Based on glass compositions, Nisyros 4 corresponds to the Lower Pumice (LPN) and Nisyros 1 corresponds to the Upper Pumice (UPN) whereas Nisyros 2 and 3 represent significant explosive eruptions in-between that have not yet been recognized on land. Application of the sedimentation-rate interpolation method to these cores yields an average age of 57.0 ± 2.9 ka for Nisyros 1 (Figure 2 Popa et al (2020). Applying our Nisyros 1 and 4 ages to core POS 513-52, the master core for the Nisyros (and Yali) marine succession because it contains all tephras in question (Figure 4c), we have determined ages of ∼63.1 ± 2 ka and ∼68.9 ± 3 ka for Nisyros 2 and 3, respectively.…”

“…Based on their earlier (Popa et al, 2019) model of explosive-effusive transition conditions, Popa et al (2020) concluded that repose times greater than ∼12 kyrs at Yali should result in subsequent effusive rather than explosive eruption. This inference may apply to the extrusion of rhyolite lava ∼12 kyrs after the Yali-2 eruption (Popa et al, 2020), because the lava bulk-rock and glass compositions are similar to, but differ in detail from, the Yali-1 tephra (Figure 12). For the ∼22 kyrs repose between Yali-1 and Yali-2, however, Popa et al (2020) did not explicitly consider the less evolved magma composition of Yali-2a and Yali-2b with respect to Yali-1 (Figures 4 and 12) which we interpret as a new magma batch after the Yali-1 eruption, as discussed below.…”