Campi Flegrei (CF) is an active volcanic caldera located in southern Italy, west of Naples, that sourced three of the largest explosive eruptions in Europe, the Campanian Ignimbrite (CI, ~40 ka), the Masseria del Monte (~29 ka) and the Neapolitan Yellow Tuff (NYT, ~14.5 ka). In proximal settings, the emplacement of these three large caldera-forming eruptions almost completely obliterated the stratigraphic record of CF eruptions that occurred between 14.5-40 ka and before 40 ka, making the record of volcanism fragmentary and incomplete. Previous studies have tentatively extended the explosive history of CF by ascribing to this caldera some tephra layers, such as the C-22 (~93 ka), X-5 (~105 ka) and X-6 (~109 ka), widely dispersed in the central-eastern Mediterranean area and representing key makers for the marine and terrestrial Quaternary archives. However, hitherto, the attribution of these tephra to the CF activity was essentially based only on the geochemical affinity with Campanian volcanics, while a definitive volcanological documentation of such deposits in proximal setting is almost completely lacking.
The aim of the present research proposal is to give a fundamental contribute in order to fill this gap of knowledge by tracing the proximal equivalents of these tephra and by stratigraphically, geochemically and geochronologically characterising them. Preliminary glass-WDS analyses of some pre-CI units cropping out in Campania Plain revealed promising correlations with the C-22, X-5 and X-6 tephra. Nevertheless, further lithostratigraphic, geochemical (major and trace elements, isotope ratios) and geochronological (40Ar/39Ar dating) analyses are required in order to confidently identify the mid-proximal equivalents of the distal tephra. Furtherly, an attempt to estimate eruptive parameters - such as column height, total erupted mass and isopachs - will be performed through an appropriate bi- and/or three-dimensional ash-dispersal Eulerian model.
A practical and explicative instance of the innovativeness and potentiality of the integrated approach that is planned to be employed in this research proposal - i.e., the combination of geochemical and geochronological investigations in mid-proximal settings with modelling of eruptions - is represented by the recent study by Albert et al. (2019). The authors, through a geochemical characterization of juvenile materials and 40Ar/39Ar dating of poorly investigated CF units, were able to identify the individual equivalent in proximal area of one of the most widespread Mediterranean tephra markers, the so-called Y-3 layer, dated at ca. 29 ka. This layer has been known in Mediterranean tephrostratigraphy and used as a regional marker since the 70s, but its origin, though supposed to be in CF, remained elusive until this recent study, where the Y-3 proximal counterpart has been identified with the Masseria del Monte Tuff (MdMT), a pyroclastic unit belonging the so called Tufi Biancastri succession, between the CI and NYT deposits. Furthermore, through computer simulations, an estimation of the magnitude and physical parameters of this previously poorly known CF eruption was for the first time proposed, revelling that the MdMT was a large explosive eruption, comparable in terms of magnitude to the NYT (i.e., 17 km3 of DRE has been estimated for the MdMT). The recognition of such a large-magnitude event, that occurred only 29 ka, showed how (i) the near-source record of volcanism at one of the most productive and dangerous volcanoes in Europe is not fully representative, and how (ii) the investigation based only on proximal records can lead to miss and/or considerably underestimate eruptive parameters and recurrence of large explosive events. Furtherly, this instance shows how only a combination of proximal and distal archives investigation can lead to a more complete and accurate understanding of past explosive volcanism in complex volcanic environments.
By using a similar approach, in this research proposal the investigation of the so-far poorly known pre-CI units occurring at CF and/or Neapolitan volcanic area is proposed. Specifically, the main objective of this project is to recognise the most-plausible near-vent proximal equivalents of the widespread C-22, X-5 and/or X-6 Mediterranean tephra, commonly attributed to the CF caldera but hitherto never found in the CF volcanic area or in relatively-proximal settings in the surrounding Campanian Plain. Indeed, the achievement of the main objective will improve the current knowledge on history, eruptive style and recurrence of large-magnitude eruptions at CF caldera, back to 110 ka. Furthermore, extending the record of the explosive activity at one of the most productive, active and dangerous volcanoes in Europe, has obvious implication in terms of hazards evaluation and risk assessment in one of the largest and most densely inhabited metropolitan area of Italy.
The potential to obtain the declared results - i.e., the identification of the mid-proximal equivalents of the marine tephra layers C-22, X-5, and X-6 - is quite high. Indeed, as mentioned before, we have already acquired some glass-WDS data for the pre-CI units allowing some preliminary correlations with the three widespread Mediterranean tephra to be proposed. In order to corroborate the correlations, further unit-specific glass-WDS analyses are required, as well as trace element characterization. The last type of analyses, along with Sr and Nd isotope ratio determination, are required in order to allow correlation between archives were the full geochemical fingerprint - i.e., major and trace elements, Sr and Nd isotope ratios - have not been determined. Furthermore, the greater the number of archives synchronized, the more accurate will be the eruption parameter modelling, for which a relatively high number of data - i.e., tephra thickness and granulometry - are needed. Finally, for 40Ar/39Ar age determinations on large and pristine k-rich minerals are required, which in mid-proximal settings are easily retrievable.