The Pomici Principali Plinian eruption (Campi Flegrei caldera, Italy): from magma processes to tephra dispersal

Stratigraphic, geochemical and petrological investigations allowed us to reconstruct pre-eruptive magmatic processes and gain insights into the tephra dispersal of the Pomici Principali eruption (11,915–12,158 cal yr BP), one of the highest-magnitude eruptions of the Campi Flegrei caldera (South Italy) over the past 15 ka. The eruption deposit comprises five members, ranging from a basal phreatomagmatic ash (Member A) to Plinian, magmatic-phreatomagmatic fallouts (Members B–C), culminating in a coarse fallout (Member D) from a ~22 km high pulsating column and phreatomagmatic ash surges (Member E) that spread both inside and outside the caldera. The products from the Pomici Principali sequence were investigated through chemical (major and trace elements) and isotopic (Sr and Nd) analyses. The acquired data allow us to shed light on the pre-eruptive processes operating in the plumbing system including rejuvenation of a residual mush left by magma feeding previous eruptions including the caldera-forming Neapolitan Yellow Tuff (~15 ka) and entrapment of xenocrysts with distinctive Sr isotopic signatures. Involvement of a mafic magma was likely able to make the mush eruptible and trigger a complex Plinian eruption. The Pomici Principali deposit represents an important, well-known Campi Flegrei caldera stratigraphic marker, because its composition can be "fingerprinted" and distinguished from other tephra layers, thus being widely recognized in the Mediterranean area. In this regard, we provide a complete chemical and isotopic dataset of the products for tephrostratigraphic purposes. Despite their overall chemical and isotopic homogeneity, detailed characterization of whole-rocks and glasses reveals subtle compositional variations from the base of the stratigraphic sequence upward, providing valuable constraints on tephra dispersal during the different phases of the eruption. Furthermore, the distinctive chemical and isotopic composition of some mineral phases represent robust tools for discriminating eruptive phases and improving proximal-distal correlations.