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Scuola di Dottorato "Archimede" in Scienze Comunicazione e Tecnologie, Ciclo XXVII,a.a. 2015-2016 Università della Calabria

A thin reddish-brown Surface Coating (SC) layer has diffusely covered many outcrops of Vulcano Island (one of the Aeolian Islands), located in the Tyrrhenian Sea, south Italy. Vulcano, in the last 120ka has been subjected to volcanic activities including both eruptions (pyroclastic and lava types in shoshonitic and leucite-tephritic series) and fumarolic degassing. The SC that has been formed on almost all these lithologies appears as a reddish (sometimes pinkish) brown glass-like rind with a greasy luster which adheres to substratum and fills and completely seals its surface irregularities. The precise formation process of the SC is what we have tried to model in the present work. The SC in Vulcano, like other active volcanic precincts, includes amorphous silica associated with a sulfate phase as jarosite mineral. Jarosite as a basic hydrous sulfate of potassium and iron is the head member of jarosite subgroup. Under the microscope, SC is consisted of a micro laminated layer (less than 1μm to 7μm in thickness) which is composed of alternative dark and light laminae. The light laminae are composed of jarosite, while the darker ones are made of almost pure silica. In many cases of the SC, the laminae encompass lenticular areas containing coarser mineral crystals and noticeable number of glass shards, very fresh to altered in different grades, within an inexplicit background. The relations between all these components (laminated portion and the trapped area between different subsets of laminae) creates some particular textures such as lentic/eye texture; convoluted texture (flow of laminae); branching, rejoining, and tee-shaped perpendicular junctions of the laminae. These particular textures are quite comparable to the patterns of Liesegang Bands in the microscopic scale. Permeability of the rock; the presence of reactants such as oxygen, iron, and sulfur; and a potential fluid to be supersaturated are required factors for developing the Liesegang bands. The porous surface of the pyroclastic deposits of Vulcano can be exposed to the acidic fluids (produced by the interaction between water and fumarolic gases) and the availability of the iron and sulfur can provide the suitable condition to form the Liesegang patterns. PhD School in Science, Communication and Technologies, Earth Sciences Curriculum, Ciclo XXVII, a.a.2014 Università della Calabria

Dottorato di Ricerca Scienze della Terra, XXI Ciclo, a.a. 2008-2009 Università della Calabria

Dottorato di Ricerca in Scienze della Terra, XXII Ciclo, a.a. 2009 Università della Calabria

Scuola di Dottorato "Archimede" in Scienze ,Comunicazione e Tecnologie, Ciclo XXVI, a.a. 2013 Università della Calabria

Scuola di Dottorato "Archimede" in Scienze ,Comunicazione e Tecnologie, Ciclo XXVI, a.a. 2007-2013 Università della Calabria

Dottorato di Ricerca in Scienze della Terra, XXIII Ciclo, a.a. 2009 Università della Calabria

International audience; We have analysed and determined the source of 138 fragments of neolithic obsidian coming from 36 sites of the French Mediterranean area (Midi). This study has required not only the development of a new non-destructive analytical method, but also the definition of the composition of the different obsidian sources in the Western Mediterranean. The method of analysis proposed is X-ray fluorescence. To eliminate surface effects due to the form of the archaeological samples, we have used the ratios of the selected elements (Nb, Y, Zr, Rb, Sr) instead of their concentrations. Discriminant diagrams allow a clear individualisation of the different domains of chemical composition, corresponding to the geological obsidians of Pantelleria, Lipari, and Sardinia. The great majority of the archaeological obsidians analysed can be attributed quite definitely to one of these three sources. Five pieces of unworked obsidian, coming from the middle reaches of the Rhône, originate quite certainly from a source exterior to the Western Mediterranean. We have not been able to localise this source.; Nous avons analysé et déterminé la provenance de 138 pièces néolithiques en obsidienne, issues de 36 sites du Midi méditerranéen de la France. Cette étude a nécessité, d'une part la mise au point d'une nouvelle méthode d'analyse non destructive et, d'autre part, la définition des domaines de composition des différentes sources d'obsidienne de la Méditerranée occidentale. La méthode d'analyse proposée est la fluorescence X. Pour éliminer les effets de surface, liés aux formes des échantillons archéologiques, on a utilisé les rapports des intensités des éléments sélectionnés (Nb, Y, Zr, Rb, Sr) au lieu de leurs concentrations. Des diagrammes discriminants permettent d'individualiser nettement divers domaines de composition chimique, correspondant aux obsidiennes géologiques de Pantelleria, de Lipari et de la Sardaigne. La grande majorité des obsidiennes archéologiques analysées se rattache nettement à l'une ou l'autre source. Cinq morceaux d'obsidienne non travaillés, trouvés dans la moyenne vallée du Rhône, proviennent très certainement d'une source extérieure à la Méditerranée occidentale qu'il n'a pas été possible de localiser.