Early Cambrian Suture Zone identified from Magnetotelluric Transects between

ALICIA FAVETTO; CRISTINA POMPOSIELLO; GISEL PERI; HERNAN BARCELONA

Darwin

Workshop; 21 Electromagnetic Induction Workshop; 2012

In different continental zones, magnetotelluric (MT) studies showed that the lithosphere is resistive (>1000Ohmm) meanwhile the top of the electrical asthenosphere. is defined by a decrease on the resistivity values(5-250 Ohmm) between 50 and 250km deep. The bulk resistivity is controlled by temperature andcomposition, but it can be enhanced by the presence of fluids (water or melt), sulfites or graphite So, the MTmethod allows to identify vertical and horizontal boundaries of crustal blocks in cratonic areas.This presentation shows the interpretation of MT data acquired along five transects in the Chacopampeanaplain that provided resistivity models crossing an Early Cambrian suture. The profiles are placed in Formosa(~S 24°), Santiago del Estero - Chaco (~ S27°), Santiago del Estero - Santa Fe (~S29.5º), Córdoba (~ S31.5°)and San Luis (~S34°) provinces.A regional characterizing was obtained from 2D models, finding a very high resistive sector, at the easternborder, with typical resistivity values for the ancient structures (>5000 Ohmm) probably associated with theRío de la Plata Craton (RPC). The thickness of the resistive zone is variable, reaching a maximum depth ofaround 140km. Below this depth the resistivity decreases showing the presence of thelithosphere-asthenosphere boundary.All lateral discontinuities observed in the resistivity models have been interpreted as the Early Cambriansuture, based on geotectonic. A tentative limit from approximately S23.5 to S34 for the western border of theRPC and the eastern border of Pampean Terrane or other block was provided from the joint interpretation ofthe models. These studies show new data about the deep structure in a region where there are no outcropsand deep geophysical studies. Furthermore, these anomalous areas are coincident with basement highs,which allowed to consider that the old crustal structures were reactivated by modern tectonic events..Keywords: Magnetolelluric, Suture, Rio de la Plata Craton, Pampean Terrane, Argentina