Fluids circulation during the variscan metamorphism of diabase dikes in the Rocroi massif (Ardennes) : a combined study of fluid inclusions and mass transfers of chemical elements
Résumé
Greenschist facies mafic dikes in the Cambro-Ordovician basement of the Rocroi Massif (southern Ardennes, France) have been used as quantitative sensors of fluid flow and fluid-rock interactions. After their consolidation, dikes have suffered a Variscan polyphase metamorphism under greenschist conditions. The major phase is a syncleavage metamorphism registered only at the dike margins. The nature and volume of metamorphic fluids were first estimated by Potdevin et al. (l99la) from mass balance calculations. Results indicate the infiltration of an H2-CO2 fluid, which caused carbonatation of the metabasite assemblage. Quartz-calcite-chlorite veins occur in the metamorphosed dikes. They are contemporary with the paragenesis of calcite, chlorite, albite, quartz and rutile of the syncleavage metamorphic stage and contain abundant fluid inclusions, some of them are rich in N1. The fluid inclusion analysis shows the circulation in tension gashes, of three main fluid types during syncleavage metamorphism. These fluid types can be classified in the following systems: H2O-Na-Cl, H2O-NaCl-N2-CH4-CO2-C2H6-H2 and N2-CH4-CO2-C2H6-H2. Results on early fluid inclusions are consistent with pressure estimations from paragenesis (P = 200 to 300 MPa). Fluid pressure between 150 and 420 MPa and temperature conditions were determined by combination of paragenesis data and chlorite geothermometry. The origin of these fluids is unclear. They could be the product of the devolatilization of enclosing rocks.
Domaines
GéochimieOrigine | Fichiers produits par l'(les) auteur(s) |
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