Magnetometric and gamma spectrometric expression of Southwestern São Francisco Basin, serra selada quadrangle (1:100.000), Minas Gerais state

Abstract

Located in the southwestern portion of São Francisco Basin, the region covered by the Serra Selada quadrangle (1:100.000) contains deformed rocks of the Neoproterozoic Bambuí Group, unconformably overlain by Cretaceous sedimentary and volcaniclastic rocks of the Areado and Mata da Corda groups, respectively. The aerogeophysical data shows two main magnetometric domains. A low frequency anomalies domain is apparently related to deep structures of Precambrian basement. High frequency anomalies represent the volcaniclastic/epiclastic deposits of Mata da Corda Group. The Bambuí Group exhibits intermediate-to-high K and Th contents (1 to 3% and 10 to 16 ppm, respectively), while U-levels are around 2.5 ppm. Significant changes in these values are caused by the distribution of rock types, tectonic features and hydrocarbon exudations. Areado Group sediments show low K (<1 %), low Th (<10 ppm) and low U (<2 ppm). Mata da Corda Group successions and associated covers exhibit very low K (sub-traces), and high Th and U concentrations (>20 ppm and >3 ppm, respectively). These values seem to be strikingly influenced by weathering processes. The performed analyses confirm the applicability of aerogeophysical data in geological mapping, and represents an important tool for the study of both the tectonic scenario and hydrocarbon accumulations in southwestern São Francisco Basin. © 2012 Sociedade Brasileira de Geofísica.