The acid sulfate zone and the mineral alteration styles of the Roman Puteoli (Neapolitan area, Italy): clues on fluid fracturing progression at the Campi Flegrei volcano
<p>Active fumarolic solfataric zones represent important structures of dormant volcanoes, but unlike emitted fluids, their mineralizations are omitted in the usual monitoring activity. This is the case of the Campi Flegrei caldera in Italy, among the most hazardous and best-monitored explosive...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-10-01
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| Series: | Solid Earth |
| Online Access: | https://www.solid-earth.net/10/1809/2019/se-10-1809-2019.pdf |
| Summary: | <p>Active fumarolic solfataric zones represent important
structures of dormant volcanoes, but unlike emitted fluids, their
mineralizations are omitted in the usual monitoring activity. This is the
case of the Campi Flegrei caldera in Italy, among the most hazardous and
best-monitored explosive volcanoes in the world, where the landscape of
Puteoli is characterized by an acid sulfate alteration that has been active at
least since Roman time. This paper provides temperature, mineralogical,
textural, compositional and stable isotope data for those solfataric
terrains sampled at the crater and Pisciarelli slope of the Solfatara
volcano between 2013 and 2019. Temperatures vary between 40 and
95 <span class="inline-formula"><sup>∘</sup></span>C. Minerals include alunite with grain sizes generally larger
than 20 <span class="inline-formula">µ</span>m, alunogen, native sulfur, well-ordered kaolinite, and,
common at Pisciarelli, pyrite, illite and <span class="inline-formula">NH<sub>4</sub></span> sulfates. Sulfate
terrains have higher contents of Ti, Ba, Au, As, Hg and Tl relative to their
parent substrate. The Pisciarelli slope is anomalous in terms of the
presence of <span class="inline-formula">NH<sub>4</sub></span>. <span class="inline-formula"><i>δ</i><sup>34</sup></span>S values for sulfides and native S
range between <span class="inline-formula">−3.00</span> ‰ and 0.49 ‰ and from <span class="inline-formula">−4.42</span> ‰ to 0.80 ‰, respectively. Sulfates show <span class="inline-formula"><i>δ</i><sup>34</sup></span>S and
<span class="inline-formula"><i>δ</i><sup>18</sup></span>O values in the range of <span class="inline-formula">−2.78</span> ‰ to 2.09 ‰ and between 4.60 ‰ and 31.33 ‰,
respectively. The style of mineralization and the stable isotope
geochemistry do produce complex and not completely consistent
classifications and genetic constraints. We merge our data with
volcanological information, data from exploration drillings and geophysical
results. With the conceptual model, we suggest a series of shallow and deep
aquifers interconnected like “communicating vessels” through a main fault
system that downthrows Solfatara with respect to Pisciarelli. Fluid outflow
from the different discrete aquifers hosted in sediments – and possibly
bearing organic imprints – is the main dataset that allows determination of
the steam-heated environment with a supergene setting superimposed.
Supergene conditions and high-sulfidation relicts, together with the narrow
sulfate alteration zone buried under the youngest volcanic deposits, point
to the existence of an evolving paleo-conduit. The data will contribute to
monitoring and evaluating the volcanic hazards.</p> |
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| ISSN: | 1869-9510 1869-9529 |