Paleocirculations in shales: a mineralogical and geochemical study of calcite veins from the Tournemire tunnel site (Aveyron, France) - Ecole Nationale du Génie de l'Eau et de l'Environnement de Strasbourg Accéder directement au contenu
Article Dans Une Revue European Journal of Mineralogy Année : 2000

Paleocirculations in shales: a mineralogical and geochemical study of calcite veins from the Tournemire tunnel site (Aveyron, France)

Résumé

Compressional Pyrenean tectonic activities induced fractures in the Toarcian shales of the experimental site in the Toumemire tunnel (Aveyron, France). A combined petrological, mineralogical and geochemical study of oriented fractures, mainly filled with calcite, allowed observation and characterisation of four mineral parageneses (calcite, calcite and framboidal pyrite, calcite and cubic pyrite, and calcite and barite). Major- and trace-element contents of the vein calcite are positively correlated with those of the host rocks, especially at the shale-marl transition. These relationships are interpreted as resulting from short-distance migrations for the considered elements (Fe, Mn, Cu, Mo, ... ). The relatively constant chemical composition of the calcite implies negligible variations in the physico-chemical crystallisation conditions. Low uranium and high iron contents of the vein calcite suggest circulation of reducing fluids. The 87Srf86Sr ratios of the vein calcite range narrowly from 0.70841 to 0.70858, favouring a buffering by the surrounding shales. The two extreme 87Srf86Sr values were determined in samples located in or near the main faulted and brecciated zone, suggesting either external inputs or different water-rock ratios. With the exception of this main faulted and brecciated zone, microfissuring most probably favoured local and limited fluid migrations.
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Dates et versions

hal-00623863 , version 1 (15-09-2011)

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Régis Mathieu, Maurice Pagel, Norbert Clauer, Laurent de Windt, Jean-Yves Boisson, et al.. Paleocirculations in shales: a mineralogical and geochemical study of calcite veins from the Tournemire tunnel site (Aveyron, France). European Journal of Mineralogy, 2000, 12 (2), pp.377-390. ⟨10.1127/ejm/12/2/0377⟩. ⟨hal-00623863⟩
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