Interpretación Geofísica (Magnética) Sierras de Chepes y de las Minas

Abstract

This report and accompanying 1:250.000 scale magnetic interpretation map covering the Sierra de Chepes, Sierra de Las Minas and the southernmost part of the Sierra Los Llanos is a product of the Geoscientific Mapping of the Sierras Pampeanas cooperative project between the Australian Geological Survey Organisation (AGSO) and the Dirección Nacional del Servicio Geológico (DNSG) of the Subsecretaría de Minería, República de Argentina. This report and map provide details on one of the three separate high-resolution, airborne geophysical survey carried out for the project, covering an area of about 9000 km2 in the southern part of La Rioja Province. The other two surveys were carried out over the northern Sierras de Córdoba (Córdoba Province) and Sierras de San Luis – Comechingones (San Luis and Córdoba Provinces), and the results are reported elsewhere (Hungerford & others, 1996 a & b). For the airborne geophysical survey, magnetic and radiometric (U, K, Th) data were obtained by World Geoscience along flight lines spaced 500m apart, from a nominal height of 100m. To assist the aeromagnetic interpretation, magnetic susceptibilities were measured during field work of exposed rock types. The magnetic data from the airborne survey were processed by Hungerford Geophysical Consultants (HGC) and radiometric data were processed by AGSO. The data were interpreted by HGC and geoscientists from AGSO at 1:1.000.000 scale and a number of geophysical domains have been identified. In conjunction, some individual aeromagnetic anomalies were modelled in order to obtain a dip and an estimation of the depth to source. The interpretation of the aeromagnetic data indicates a regional geological discontinuity between the granitoids and metasediments of Sierra de Chepes and Los Llanos in the north and the granitoids of Sierra de Las Minas in the south. The rocks in the north are generally more magnetic, and in the south there is evidence for a large domain associates with granitoids which either is remanently magnetised or is underline by a very low magnetic granitoids or metasediments.