Étude structurale et metallogénique des gisements d'émeraude de Colombie : contribution à l'histoire tectono-sédimentaire de la cordillère orientale de Colombie

Abstract : The Colombian emerald deposits, hosted in the Lower Cretaceous series, form two zones along the western and eastern flanks of the Eastern Cordillera (western and eastern zones). Within both zones, metallogenic processes, hydrothermal fluid composition and fluid-rock interaction are similar. However, detailed structural mapping and geometric analysis evidenced that structural controls synchonous with the mineralization are drasticaly different from the western to the eastern zone: the western emerald deposits, as the Muzo and Coscuez ones, are characterized by compressive structures formed along tear faults, whereas the eastern emerald deposits, as the Chivor one, present extensional structures branched on a brecciated level which acted as a local detachment, gravity driven. This brecciated level corresponds to an evaporite dissolution residue. Petro-structural studies of veins and breccias show that high fluid pressures enhanced the propagation of the thrusts within the western deposits, where fluidization phenomena and associated hydraulic fracturing occurred. Regional cross-sections coupled with radiometrie datating of the emerald deposits show that : 1) at the time of the Eocene-Oligocene boundary, when the western deposits formed, the western side of the Eastern Cordillera became a fold-and-thrust belt and experienced clockwise bloc rotations, prior to the major uplift of the Cordillera during the Andean phase (middle Miocene) ; 2) on the eastern side of the Cordillera, the emerald deposits are hosted in an unic regional stratigraphic level containing evaporites. The emerald mineralization occurred at the time of the Cretaceous-Tertiary boundary, during a thin-skinned extensional tectonic event. This event predates the Andean major uplift of this eastern part of the Cordillera. In this area, Andean uplift results from right-lateral transpressional tectonics.
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Yannick Branquet. Étude structurale et metallogénique des gisements d'émeraude de Colombie : contribution à l'histoire tectono-sédimentaire de la cordillère orientale de Colombie. Sciences de la Terre. Institut National Polytechnique de Lorraine, 1999. Français. ⟨NNT : 1999INPL048N⟩. ⟨tel-01749901⟩

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