TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 51 (No. 10), pp. 1047-1058, 1999

Geoelectric structure beneath limestones of the Sao Francisco Basin, Brazil

J. M. Travassos1 and P. T. L. Menezes2

1CNPq-Observatorio Nacional, 20921-400 Rio de Janeiro, Brazil
2FGEL/UERJ, 20559-900 Rio de Janeiro, Brazil

(Received November 30, 1998; Revised June 16, 1999; Accepted July 6, 1999)

Abstract: A reconnaissance MT survey was conducted in the southern portion of the Sao Francisco Sedimentary Basin, Brazil, for mapping the subsurface structure. The objective was to provide a regional model and in helping to select areas to be further surveyed with seismics. The data collected at seven EMAP-style spreads of 500 m, with an average spacing of 30 km. The field procedure allowed for the correction of statics and the production of 7 inverted models, smooth representations of the regional structure as seen below each site. A 2-D forward model tested and refined the regional structure revealed by the inversions and yielded an earth composed of 4 main geologic units. A 100 ohm.m limestone layer on the top of 20 ohm.m shales, followed by a 1000–200 ohm.m structured basement. Crustal resistivities do not change until reaching depths of more than 30 km. The model ends at a conductive half-space of 30 ohm.m. A suture zone between an orogenic belt and the Sao Francisco craton was modeled below the sedimentary section bringing its know limits 60 km to the east.

Corresponding author E-mail: jandyr@on.br

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