Publication Date:
2017-04-04
Description:
The Astroni volcano was built through seven eruptions that generated pyroclastic deposits and lava domes
within the Campi Flegrei caldera (southern Italy) 4.1–3.8 ka BP. Whole-rock geochemical and B–Sr–Nd
isotopic investigations were carried out on representative samples of all seven eruptions. The products vary
from tephriphonolites to phonolites, and from latites to trachytes. They show textural, mineralogical and
isotopic evidence of disequilibrium, including distinct clinopyroxene populations, rounded and/or resorbed
plagioclase and alkali-feldspar, and reverse-zoned phenocrysts of all these mineral phases. The Sr, Nd and B
isotopic composition of whole rocks is variable and correlated with the degree of chemical evolution,
suggesting open-system processes in addition to fractional crystallisation. Moreover, significant Sr-isotopic
disequilibrium between the phenocrysts and glass has been documented for one sample.
The chemostratigraphy of the products indicates that Astroni eruptions 1 through 5 were fed by magmas of
trachytic to phonolitic composition that were less enriched in radiogenic Sr and 11B up-section. This
variability has been interpreted as the result of mingling between at least two distinct magmatic endmembers,
one more evolved and the other less evolved. Another heterogeneous batch of magma, resulting
from almost complete mixing between the same two end-members, was drained during eruptions 6 and 7.
The more evolved end-member, characterised by 87Sr/86Sr≥0.7075, 143Nd/144Nd≤0.51247 and δ11B≥−8‰,
was very similar to the magma that fed the final phases of the Agnano–Monte Spina eruption, which
occurred a few centuries earlier in the Astroni vent area. The less evolved end-member had 87Sr/
86Sr≤0.70726, 143Nd/144Nd≥0.51251 and δ11B≤10‰, and was likely derived by fractional crystallisation of a
mantle-derived magma. An abrupt decrease in both the Sr isotope ratio and the Th content, detected at the
transition between Unit 4 and 5, suggests that another magma with a 87Sr/86Sr ratio intermediate between
those of the two identified end-members may have been involved in Astroni activity. The more evolved endmember
is interpreted as a residue of the Agnano–Monte Spina eruption that was invaded by either the
intermediate or the less evolved magmatic end-member, promoting mingling and triggering Astroni activity.
This study of Astroni provides insights for both short- and long-term volcanic hazard assessment, as the
Astroni volcano is the best example of a very close sequence of eruptions from the same vent area in the
Campi Flegrei caldera.
Description:
Published
Description:
135–151
Description:
2.3. TTC - Laboratori di chimica e fisica delle rocce
Description:
3.5. Geologia e storia dei vulcani ed evoluzione dei magmi
Description:
JCR Journal
Description:
reserved
Keywords:
Campi Flegrei caldera
;
B–Sr–Nd isotope geochemistry
;
Magma mingling/mixing
;
Chemostratigraphy
;
04. Solid Earth::04.08. Volcanology::04.08.03. Magmas
;
04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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