Open-system magma evolution and fluid transfer at Campi Flegrei caldera (Southern Italy) during the past 5 ka as revealed by geochemical and isotopic data: The example of the Nisida eruption

We have carried out a detailed petrological investigation on products of the poorly understood Nisida eruption, one of the most recent volcanic events (similar to 4 ka BP) at Campi Flegrei caldera. We present major oxide contents and Sr-Nd isotopic data determined on bulk rock, groundmass and separated phenocrysts, along with major and volatile elements (H2O Cl, S and CO2) content of clinopyroxene-hosted melt inclusions from pumice fragments representative of the eruption. We use these to elaborate the role of magmatic evolution processes and fluid transfer prior to, and during, the Nisida eruption. The results indicate that the eruption was triggered by the arrival of a volatile-rich, shoshonite-latite magma. This magma was similar in terms of Sr and Nd isotopes (Sr-87/Sr-86 similar to 0.70730; Nd-143/Nd-144 similar to 0.51250) to the Astroni 6 magmatic component. We infer that emplacement of this magma triggered resurgence of the caldera floor, and fed a large part of the volcanic activity at Campi Flegrei caldera during the past 5 ka. The new data on the Nisida eruption and other recent eruptions at Campi Flegrei, together with published data, suggest that fractional crystallization, and potentially fluid transfer from deep to shallow depths may account for most of the chemical variability of the erupted melt. Additional processes, such as magma mingling/mixing, and/or entrapment of antecrysts into the magma prior to the Nisida eruption are required to explain the large isotopic variation displayed by the analyzed products. The Nisida eruption occurred in the eastern sector of the resurgent Campi Flegrei caldera. In this sector, presently affected by an extensional stress regime, previous studies suggest that a Nisida-like eruption would be likely if the level of activity in the caldera were to intensify. In an area with such structural conditions, the ascent of a volatile-rich magma such as that which erupted at Nisida should generate geophysical and geochemical signals detectable by an efficient monitoring network. The results of this investigation should inform the study of other active calderas worldwide that are experiencing persistent unrest, such as Rabaul, Aira, Iwo-Jima, Santorini, Long Valley and Yellowstone. (C) 2016 Elsevier B.V. All rights reserved.