Insights into caldera cycles obtained from the eruption ages and chemistry of the youngest products of Nisyros volcano, South Aegean Arc

Hazards posed by volcanism are strongly associated with the volcanoes' shifts in eruptive styles, as they often alternate between effusive and explosive activity with little to no forewarning. These shifts are thought to be governed by processes happening in conduits and reservoirs feeding magmas to the surface. In hope to forecast eruptive activity (including styles), it is critical to better understand these governing processes. Here, we consider the case study of Kos-Nisyros-Yali volcanic field (Aegean Arc), which has experienced several caldera-collapse events in the last few hundreds of thousands of years and undergone multiple shifts in eruptive style. We conduct bulk-rock geochemical analyses and U-Th disequilibrium dating of zircon on eight of the post-caldera domes, which form the youngest volcanic deposits on Nisyros, to better understand the most recent stage of activity at this volcano and its implications on future eruptions. Zircon U/Th ages indicate that the domes formed between ca. 26 ka and 13 ka, 30 ky after the volcano's most recent caldera-collapse eruption. We observe a spatial migration of vents as well as a slight shift to more mafic bulk-rock compositions with time, which could reflect a growing influence of persistent mafic recharge pulses into the upper-crustal magma chamber throughout the eruptive period. Based on the eruption timings, compositions of fumaroles, and recent observations during unrest on Nisyros, we suggest that the upper-crustal magma reservoir is currently in a water-saturated state, which favors its growth and infrequent effusive eruptions.