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Rejuvenation of the Kos-Nisyros-Yali magmatic system after the caldera collapse events on Nisyros

Sam Winsemius , Razvan-Gabriel Popa, Olivier Bachmann

Abstract

Caldera--forming eruptions rank among Earth's most catastrophic volcanic events, but despite the danger they pose, they are not yet fully understood. They are believed to follow recurrent evolutionary paths, called caldera cycles, comprising multiple stages. The focus of this presentation is the stage following a caldera collapse event, which can either lead to the rejuvenation or death of a system. Kos-Nisyros-Yali is the largest active magmatic system in the Aegean Sea, which underwent several caldera collapses, including a major catastrophic event at 161 ka. Here, attention is given to the latest caldera-forming event in this system, namely the Upper Pumice eruption on Nisyros at 58.4±2.7 ka. Roughly simultaneously to the rhyolitic Upper Pumice eruption, a relatively dry and hot andesite lava (~1050±30◦C), pre-eruptively stored at upper crustal conditions, erupted outside the Nisyros volcano, forming the small island of Agios Antonios at 59.7±6.5 ka (ulvospinel-ilmenite U-Th dating). The lava is more primitive than the contemporaneous units on Nisyros-Yali, resembling their recharge enclaves. This suggests that the latest caldera-collapse on Nisyros is associated with the voluminous effusion of recharge magmas, and thus indicates that after the caldera-collapse event, the upper-crustal silicic mush was rejuvenated. The influx of recharge magmas led to the formation of a second eruptible magma chamber, feeding the younger Yali volcano, its zircon and ulvospinel crystallization timescales being distinct from those of Nisyros (younger than the andesitic lava). This is supported by crystallization timescales determined in an explosive unit on Agios Antonios and in the other Yali units.