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The increasing application of cryptotephra studies is leading the identification of new tephra marker layers the sources of which in many cases may not be known or may be ambiguous. In this contribution, we discuss the controls on tephra geochemistry in the context of establishing the provenance of an unknown tephra layer. We use the RESET database ( https://c14.arch.ox.ac.uk ), which contains major and trace element data for a number of European silicic tephra erupted in the period 100 ka to ca 10 ka, to define new and modify existing tectonic setting discrimination diagrams for use with volcanic glass analyses. Bivariate plots of the elements Rb, Nb, Ta, Y and Th and K 2 O, SiO 2 , FeO and MgO can be used to identify tephra from different tectonic settings. New, detailed glass chemistry shows that tephra from the productive Neapolitan volcanic centres, Somma-Vesuvius (22–4 ka activity), Campi Flegrei (60–15 ka) and Ischia (75–20 ka), can be separated using major elements, CaO–SiO 2 , Na 2 O/K 2 O–CaO and CaO–MgO. In each of these centres, the tephrostratigraphic record is characterized by the repeated occurrence of similar glass compositions, punctuated by significant changes in magma chemistry. The glass compositions of successive eruptions from Campi Flegrei are similar but there is a significant change in the composition following the Campanian Ignimbrite, and there are comparable compositional changes at Ischia following the Monte Epomeo Green Tuff eruption and at Somma-Vesuvius following the Verdoline event. Distinguishing different tephras from a single volcanic centre is more problematic, and in some instances even impossible, without good chronological and stratigraphic control and/or high-resolution trace element glass data. At Somma-Vesuvius certain major elements can be used to separate glasses from the major chronological phases (Group 1 – Pomici di Base and Verdoline; Group 2 – Mercato and Avellino), but separating tephras within a single group on the basis of glass composition can be problematic. [ABSTRACT FROM AUTHOR]

Abstract: The Campi Flegrei caldera collapsed 39ka in the Neapolitan area (southern Italy) after the Campanian Ignimbrite eruption. This eruption, recognized as the largest and the most cataclysmic volcanic event in the Mediterranean area over the past 200ka, extruded not less than 300km3 of trachytic magma. Controversy exists over the timescales required to assemble such large volume of silicic melt and thus whether large magmatic reservoirs can actually persist below active volcanic systems over prolonged periods of time. Uranium-series analyses have been performed on Campanian Ignimbrite whole-rocks, glass matrixes and separated minerals, and the obtained results have been interpreted in combination with data on Sr, Nd, and Pb isotopes from literature. The compositionally most evolved sample which is most radiogenic with respect to Sr isotopes records a reference age of 71ka. By contrast, U–Th internal isochrones of the three compositionally least evolved samples give identical initial Th isotope ratios and yield consistent ages predating the eruption by up to 6.4ka. The highest Pb and Nd isotopic ratios and 230Th/232Th activity ratios together with the oldest reference age of the most evolved samples suggest the existence of a resident magma body possibly related to a magmatic system that is known to have fed earlier magmatic activity in the Campi Flegrei area. Conversely, the younger age of the least evolved and least radiogenic magma dates the crystallization/differentiation event of a chemically and isotopically new magma batch entering the reservoir of the resident magma some few thousand years before the cataclysmic eruption. Therefore, the time preceding this large caldera-forming eruption during which the large volume of Campanian Ignimbrite magma assembled and mixed is 6.4±2.1ka. [Copyright &y& Elsevier]