Resumo

PEREZ LUJAN, Sofía et al. Velocidades sismicas de las unidades aflorantes en el flanco occidental de la Sierra de la invernada, precordillera de San Juan. Rev. Asoc. Geol. Argent. [online]. 2013, vol.70, n.2, pp.173-191. ISSN 0004-4822.

P-wave seismic velocity (Vp) determinations are shown in this work for a region in the western flank (Don Carmelo nature reserve) of the la Invernada range in the Ullúm Department of the San Juan Province. The velocities obtained using the seismic refraction method indicate Vp values of 550; 1.670 and 4.134 m/s and thicknesses of 1 m and 7 m approximately, for a two-layer over a higher Vp half space model. The exposed units show greywacke and well compacted sandstones, which have a good correlation with the deepest and higher Vp values of the seismic model. Also the lowest Vp values are consistent with alluvial material located in the shallower seismic layers (< 7m depth). Other units observed on the surface exhibit outcrops of diabases and gabros, which were not geophysically explored. However, a comparison between the observed lithologies and Vp values with a global database predicts the continuation at depth of mafic rocks associated with even higher Vp values than those determined at the surface. These results are of interest because they help us to identify an ophiolite belt in the Precordillera, a region presently characterized by an overthickened crust of 64 km.

Palavras-chave : Seismic refraction; Basement; P waves; Ophiolite; Precodillera; Petrology; Geophysics.

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