Combined use of the centroid and matched filtering spectral magnetic methods in determining thermomagnetic characteristics of the crust in the structural provinces of Central Brazil

Spectral analysis of data acquired in twelve different aeromagnetic surveys of central Brazil has led to new insights in the magnetic characteristics of the lithosphere in the structural provinces of Tocantins and São Francisco. Since centroid-based spectral magnetic methods do not model the spectrum explicitly, they are used for the first time in conjunction with the matched filtering spectral modeling method to verify that appropriate slope segments are fit when determining source depths. The Tocantins province is characterized by subdued variations in the thickness of magnetized layers, most of which may be associated with structural discontinuities and subcrustal intrusions. In contrast, variations in thickness of magnetized crustal layers are more prevalent in the São Francisco province. The depths to the bottom of magnetized crust in the Tocantins province are, in general, less than 30-35. km, whereas they reach depths greater than 40. km in the São Francisco province. In parts of São Francisco craton, the depths to the bottom of magnetized crust are greater than the crustal thickness determined from seismic refraction and receiver function studies. However, these are indistinguishable in terms of resolution of the two methods. Analysis of heat flow data and results of thermal modeling indicate depths of Curie isotherms consistent with estimates from spectral analysis of aeromagnetic data. Hence the possibility that the uppermost part of mantle under the São Francisco craton may be ferromagnetic cannot be dismissed.