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http://hdl.handle.net/2122/7339
Authors: | Freda, C.* Gaeta, M.* Giaccio, B.* Marra, F.* Palladino, D.* Scarlato, P.* Sottili, G.* |
Title: | CO2-driven large mafic explosive eruptions: a case study from the Colli Albani Volcanic District (Italy) | Journal: | Bulletin of Volcanology | Series/Report no.: | /73 (2011) | Publisher: | Springer | Issue Date: | 2011 | DOI: | 10.1007/s00445-010-0406-3 | Keywords: | Mafi c explosive erupt ions Py roclasti c flow Er uption magni tude Colli Al bani Po tassic volcan ism Car bonate assi milation |
Subject Classification: | 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions | Abstract: | Gene rally, the intensity and magnitude of explosive volcanic activity increase in parallel with SiO2 content. Pyro clasti cflow-forming eruptions in the Colli Albani ultrapotassic volcanic district (Italy) repres ent the most striking exception on a global scale, with volumes on the order of tens of cubic kilometres and K-foiditic compositions (SiO2 even<42 wt.%). Here, we reconstruct the pre-eruptive scenario and event dynamics of the ~456 ka Pozzolane Rosse (PR) eruption, the largest mafic explosive event of the Colli Albani district. In particular, we focus on the driving mechanisms for the unusually explosive eruption of a low-viscosity, mafic magma. Geologic, petrographic and geochemical data with mass balance calculations, supported by experimental data for Colli Albani magma compositions, provide evidence for significant ingestion of carbonate wall rocks by the Pozzolane Rosse K-foiditic magma. Moreover, the scattered occurrence of cored bombs in Pozzolane Rosse pyroclastic-flow deposits records carbonate entrainment even at the eruptive time scale, as also tested quantitatively by thermal modelling of magma–carbonate interaction and carbonate assimilation experiments. We suggest that the addition of free CO2 from decarbonation of country rocks was the major factor controlling magma explosivity. High CO2 activity in the volatile component, coupled with magma depressurisation, produced extensive leucite crystallisation at short time scal s, resulting in a dramatic increase in magma viscosity and volatile pressurisation, which was manifested a change of eruptive dynamics from early effusion to the Pozzolane Rosse's highly explosive eruption climax. |
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