In the present work we report results of a regional scale investigation of the thermal and magnetic characteristics of the crust in the southern sector of the geologic provinces of Tocantins and S？o Francisco, Brazil. Updated compilations of aeromagnetic and geothermal data sets were employed for this purpose. Use of such techniques as vertical derivative, analytic signal, and Euler deconvolution in analysis of aeromagnetic data has allowed precise locations of the sources of magnetic anomalies and determination of their respective depths. The anomalies in the Tocantins province are considered as arising from variations in the magnetic susceptibilities and remnant magnetizations of alkaline magmatic intrusions of the Tertiary period. The lateral dimensions of the bodies are less than 10 km, and these are found to occur at shallow depths of less than 20？km. On the other hand, the anomalies in the cratonic areas are related to contrasts in magnetic properties of bodies situated at depths greater than 20？km and have spatial dimensions of more than 50 km. Analysis of geothermal data reveals that the cratonic area is characterized by geothermal gradients and heat flow values lower when compared with those of the Tocantins province. 1. Introduction The geotectonic provinces of S？o Francisco and Tocantins are often considered as the main structural units in the eastern part of the South American platform [1, 2]. Geological and geophysical studies performed to date have allowed mapping of structural and tectonic features near the surface of these structures, but little is known about the vertical distributions at depths in the crust. One of the convenient ways of circumventing this difficulty is to evaluate aeromagnetic survey data and compare the results with those of geothermal studies. According to available information [3, 4] past attempts to integrate the results of aeromagnetic surveys were limited to incorporating standard corrections of technical operations. It became clear that a detailed review of aeromagnetic survey data is needed, focusing on the judicious use of corrections (leveling and microleveling, eliminating the effects of diurnal variation and the internal field) and use of advanced techniques of interpretation (vertical derivative, analytic signal, and Euler deconvolution). Also, “suture” techniques need to be employed in integration of data from several surveys in this area in obtaining a coherent analysis of the subsurface geological significance of the results and its correlations with structural features. Another parallel objective of
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