Microstructures in vein systems associated with compressional tectonics in the Andean foothills. Tierra del Fuego.

CERREDO, M. E.; TASSONE A.; LODOLO E.; LIPPAI, H.;

Buenos Aires

Otro; X Reunión sobre microtectónica, Arturo J. Amos; 2001

Comisión de Tectónica de la A.G.A

The southernmost Andes of Tierra del Fuego underwent a Late Cretaceous to Early Tertiary regional crustal shortening which resulted in the building of a fold-and-thrust belt. In the Argentinean part of the island the thrusts, with a general WNW-ESE trend, root a detachment within the shales and mudstones of the Early Cretaceous Yahgán Formation. In the Andean foothills, around the southeastern eastern end of Lago Fagnano, the Yahgán mudstones host multiple sets of thin (<1cm) veins with quartz and carbonate infillings, the oldest of which often display a discontinuous box fold pattern. The complex vein network includes both oblique and bedding-parallel arrays. The earliest veins show coarse-grained primary growth textures which are variably overprinted by plastic, brittle and dissolution-precipitation microstructures. The geometry and internal fabrics of the different vein systems record repeated episodes of dilation, sealing and shearing which are interpreted as associated with the major Andean compression. Posthumous, straight, oxide-filled fractures as well as closely spaced joints are inferred to be related to the Fagnano Fault System strike slip activity