CONICET | Buscador de Institutos y Recursos Humanos

In this paper attention is focused upon dykes of carbonate fault breccia from the Cerro La Chilca area, Eastern Precordillera, central-western Argentina, which provide some clues on the probable mechanism of both fault movement and dyke injection. Breccia dykes are seen intruding Upper Carboniferous sedimentary rocks, as well as in the Triassic La Flecha Trachyte Formation. The timing of breccia dyke emplacement is constrained between the uppermost Triassic and the Early Miocene. The study presented here supports a tectonic-hydrothermal origin for these breccia dykes; fragmentation and subsequent hydraulic injection of fluidized breccia are the more important processes in the entire breccia dykes development. Brecciation can be triggered by seismic activity which acted as a catalyst. The escape of fluidized material must be attributed to high hydrostatic pressure establishing the direction of least pressure. Previous studies have shown that cross-strike structures have had an important role in the evolution of this Andean segment since at least Triassic times. These structures represent pre-existing crustal fabrics that could have controlled the emplacement of the dykes. The dykes, which are composed mostly of carbonate fault breccia, were evidently injected upward along WNW fractures.

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