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

摘要

Spectral analysis of data acquired in twelve different aeromagnetic surveys of central Brazil has led to new insights in themagnetic characteristics of the lithosphere in the structural provinces of Tocantins and S?o Francisco. Since centroid-based spectralmagneticmethods do notmodel the spectrumexplicitly, 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 S?o 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 S?o Francisco province. In parts of S?o Francisco craton, the depths to the bottomof magnetized crust are greater than the crustal thickness determined fromseismic refraction and receiver function studies. However, these are indistinguishable in terms of resolution of the two methods. Analysis of heat flowdata and results of thermalmodeling 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 S?o Francisco craton may be ferromagnetic cannot be dismissed.