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Solid Earth An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 08 May 2019

Research article | 08 May 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Solid Earth (SE).

The acid-sulfate zone and the mineral alteration styles of the Roman Puteolis (Neapolitan area, Italy): clues on fluid fracturing progression at the Campi Flegrei volcano

Monica Piochi1, Angela Mormone1, Harald Strauss2, and Giuseppina Balassone3 Monica Piochi et al.
  • 1Osservatorio Vesuviano, Istituto Nazionale di Geofisica e Vulcanologia, Naples, I-80124, Italy
  • 2Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität, Münster, 48149, Germany
  • 3Dipartimento di Scienze della Terra, dell'Ambiente e delle Risorse, Università Federico II, Naples, I-80134, Italy

Abstract. Active fumarolic solfataric zones represent important structures of dormant volcanoes, but unlike emitted fluids, their mineralization are omitted in the usual monitoring activity. This is the case for the Campi Flegrei caldera in Italy, among the most hazardous and best-monitored explosive volcanoes in the World, where the landscape of Puteolis is characterized by acid sulfate alteration that is 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 2012 and 2019. Temperatures vary between 40° and 95 °C. Minerals include alunite with grain sizes generally larger than 20 µm, alunogen, native sulfur, well-ordered kaolinite, and, common at Pisciarelli, pyrite and NH4-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 NH4. δ34S values for sulfides and native S range between −3.00 and 0.49 ‰ and from −4.42 to 0.80 ‰, respectively. Sulfates show δ34S and δ18O values in the range of −3.35 to 3.80 ‰ and between 0.3 and 31.33 ‰, respectively. The style of mineralization and the stable isotope geochemistry do produce complex and not completely consistent classifications and genetic information. 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 biological imprints – is the main dataset that allows determination of the steam-heated environment with a supergene settings 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 a paleo-conduit. The data will contribute to monitor and evaluate the volcanic hazards.

Monica Piochi et al.
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Monica Piochi et al.
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Short summary
The Campi Flegrei caldera in Italy displays a high temperature acid sulfate alteration zone developing in its most active sector. Repeated surveys of hydrothermal mineralizations conducted between 2012 and 2019 allow evaluating the volcano dynamics. A steam-heated environment dominates a paleo-conduit in the area. The fluid supply derives from shallow and deep aquifers interconnected like communicating vessels.
The Campi Flegrei caldera in Italy displays a high temperature acid sulfate alteration zone...