Insights into the explosive eruption history of the Campanian volcanoes prior to the Campanian Ignimbrite eruption

Abstract

The Campanian Volcanic Zone (CVZ) comprises multiple active volcanoes and includes the highly productive Campi Flegrei and Ischia caldera systems. These caldera volcanoes have produced probably the largest eruptions in Europe in the past 200 ka, such as the Monte Epomeo Green Tuff (MEGT; Ischia) at ca. 56 ka and the Campanian Ignimbrite (CI; Campi Flegrei) at ca. 40 ka, which form widespread isochrons across the Mediterranean region. These closely-spaced volcanic centres erupt phonolitic to trachytic glass compositions that are similar, and thus it can be challenging to correlate tephra deposits to specific volcanic sources. Here we present a detailed tephrostratigraphy for pre-CI eruption activity using the units preserved within a sequence at the coastal Acquamorta outcrop, on the western side of the CI caldera rim. Both the MEGT and CI units are present in the section, and they bracket twelve eruption units that were logged and sampled. New major and trace element glass chemistry data have been acquired for these Acquamorta tephra deposits. Three eruption deposits from Ischia and nine from Campi Flegrei are identified, which helps constrain the tempo of volcanic activity of these centres between the large caldera-forming eruptions. The three Ischia tephra deposits between the MEGT and the CI are indistinguishable based on both major and trace element glass chemistry and cannot be correlated to a specific or known eruption in this interval, such as the Schiappone tephra. The compositional variations between the Campi Flegrei eruptions reveal temporal shifts in the composition of the tephra deposits that reflect changes in the magmatic system prior to the CI eruption. These deposits indicate that there were at least nine eruptions at Campi Flegrei within 16 ka of the enormous CI eruption, and suggest that there was no significant period of repose before the caldera generating eruption.