Magnetotelluric evidences for the suture between the Río de la Plata and the Pampean cratons at 31º 40´, Córdoba province, Argentina

LÓPEZ DE LUCHI, M.G, ; POMPOSIELLO, M.C.; FAVETTO, A.; BOOKER, J.

Barcelona, España

Simposio; 6th International Symposium on Andean Geodynamics, (ISAG 2005; 2005

Institut de recherche pour le developpement, Universitat de Barcelona

Magnetotelluric (MT) soundings were made at 29 sites along an almost west-east profile at around 31.5º SL which extended from La Rioja to Santa Fe provinces in central Argentina. The profile cuts two main crustal domains: the Pampean terrane to the west and the Río de la Plata craton to the east. The objectives of the MT study are to define the nature of the boundary and the electrical resistivity structure of the crustal domains. The MT data set on apparent resistivity is used to define the geoelectrical structures in the region. Apparent resistivity responses indicate the ca 2.3-2.6 Ga Río de la Plata craton  contains extremely resistive crust whereas the Pampean terrane present a 4km layer of the most resistive rocks that were measured and changes in depth into a less resistive sector. Between 140-160 km a subvertical limit between the RIC and the PAT runs approximately along the border of the Sierra Chica .To the east of the zone a highly resistive crustal segment the RIC>grades into a sector of relatively enhanced conductivity below the Chaco?Paranaense basin. To the west the more resistive crustal segment is thinner and an area of enhanced conductivity appears below the block of the Sierra Grande de Córdoba. Based in these evidence the sharp lateral discontinuity observed in the resistivity model is conjectured to represent the suture between the RIC and the PAT. Our results in combination with the geological information suggest that the boundary between the RIC and the PAT is located at the east of the Sierras de Córdoba. In consequence the meaning of the ophiolite belts as representing crustal scale sutures remains unsolved.