Magnetotelluric Study in the Western Border of the Río de la Plata Craton (Chacopampeana Plain and Eastern Sierras Pampeanas)

C. POMPOSIELLO; A. FAVETTO; V. PERI; H. BARCELONA; L. OROZCO

Tandil

Encuentro; Second Biennial Meeting of the Latin-American Association of Paleomagnetism and Geomagnetism (LATINMAG); 2011

The electric resistivity provides a valuable constraint to define mantle structure, this information isindependent of the one obtained by seismology or other geophysical techniques. The bulk resistivity is controlled by temperature and composition, but it can be enhanced by the presence of fluids (water or melt), sulfites or graphite. Magnetotelluric (MT) studies performed in different continental zones showed that the lithosphere is very resistive (> 1000 ohm-m) and it was observed a decrease on the resistivity values (5-25 ohm-m) between 50 and 250 km deep, defining the top of the electrical asthenophere. So, the MT method becomes an useful tool to identify vertical and horizontal boundaries of crustal blocks in cratonic areas.This paper presents two dimensional (2D) inversion of MT data acquired along four transects in the Chacopampeana plain that provided resistivity models crossing the western border of Rio de la Plata Craton (2.1-2.3 Gy). The profiles are placed in Formosa (~ 24 ° LS), Santiago del Estero - Chaco (~ 27 ° LS), Córdoba (~ 31.5 ° LS) and San Luis (~ 34 ° LS) provinces.A regional characterizing was obtained from models, finding a very high resistive sector, at the eastern part, with typical resistivity values (>5.000 Ohm-m) for the ancient structures corresponding to the Río de la Plata Craton. The thickness of the resistive zone is variable, reaching a maximum depth of around 140 km. Below this depth the resistivity decreases showing the presence of the listosphere-astenophere boundary.