Magnetic Anomalies in the Structural Provinces of Tocantins and San Francisco of Central Brazil - Results from Spectral Analysis of Aeromagnetic Data

In this work we report progress obtained in understanding the thermal structure of crust in two geologic provinces of central Brazil: Tocantins (eastern segment) and San Francisco. The study is based on spectral analysis of aeromagnetic data, obtained in 12 different surveys. The technique employed in data analysis is the scaled spectral slope method (Bhattacharyya and Leu, 1975, 1977). It allows determination of the depths to top and bottom of magnetized crust. According to the model results the depths to the bottom of magnetic sources fall in the range of 30-45 km in the province of Tocantins while it is in the range of 40-60 km in the province of San Francisco. The differences in depth values are considered indications of a systematic change in the deep thermal structures of these provinces.