Publication Date:
2021-12-06
Description:
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 K2O, SiO2, 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 (22e4 ka activity), Campi Flegrei (60e15 ka)
and Ischia (75e20 ka), can be separated using major elements, CaOeSiO2, Na2O/K2OeCaO and CaOeMgO.
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 e Pomici di Base and Verdoline; Group 2 e Mercato and
Avellino), but separating tephras within a single group on the basis of glass composition can be
problematic.
Description:
Published
Description:
48-66
Description:
1V. Storia eruttiva
Description:
JCR Journal
Keywords:
Tephrochronology
;
Major and trace element
;
Discrimination diagrams
;
Somma-Vesuvius
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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