Typology of the granitic stones of the cathedral of Evora (Portugal): A combined contribution of geochemistry and Fe-57 Mossbauer spectroscopy - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Journal of Cultural Heritage Année : 2002

Typology of the granitic stones of the cathedral of Evora (Portugal): A combined contribution of geochemistry and Fe-57 Mossbauer spectroscopy

Résumé

A geochemical study, including a detailed investigation of Fe by Mössbauer spectroscopy, was undertaken to characterise the different varieties of the stones in the cathedral of Évora (Portugal). Ten representative stone samples were collected. Bulk analytical techniques, including ICPES, INAA and XRF, were performed, as well as Mössbauer spectroscopy. The stones have consistent linear geochemical variations, well constrained by a limited number of inter-element ratios involving Ti, Mg, Fe and Al. Taking into account the REE distribution, the Mg, Fe and Ti contents and the Fe3+/Fe2+ ratio, two types of stones were distinguished. The type-1 stones show REE normalised patterns with negative Eu anomaly, and are relatively Al rich. The type-2 stones without Eu anomaly, more REE fractionated, are relatively LREE, TiO2, MgO and Fe2O3 rich. In agreement with the geochemical results, the Mössbauer data have shown that the Fe3+/Fe2+ ratio was correlated with the magmatic differentiation and further suggested that the presence of Fe (Ti) oxides is related to a higher magmatic evolution. Both stone types have a MgO/TiO2 ratio close to 2, which is characteristic of calco-alcaline granite. The chemical inter-element variation along the same constant ratio, as well as the REE pattern and the Fe oxidation state, seems to indicate a magmatic filiation from type-2 to type-1 stones. The combination of REE patterns and Fe/Mg, Ti/Mg and Fe3+/Fe2+ geochemical indexes could be used as efficient discrimination tools for other stones of monuments built of granite.

Dates et versions

hal-01350637 , version 1 (01-08-2016)

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Citer

Mohamed Nasraoui, João C. Waerenborgh, M.I. Prudêncio, Essaïd Bilal. Typology of the granitic stones of the cathedral of Evora (Portugal): A combined contribution of geochemistry and Fe-57 Mossbauer spectroscopy. Journal of Cultural Heritage, 2002, 3 (2), pp.127-132. ⟨10.1016/S1296-2074(02)01167-6⟩. ⟨hal-01350637⟩
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