Audiomagnetotelluric Investigation of the Colonia Depression, Săo Paulo - Brazil

About 35 km of Metropolitan Săo Paulo (SE Brazil), in the Precambrian cristalline basement, there is a striking circular morphological depression, with a diameter of 3.64 km. Based on previous geological and geophysical investigations it is believed that the origin of the Colonia ringstructure is an impact of a meteorite. The depression is filled with quaternary deposits rich in clay and organic components. In order to estimate the depth of the basement, a total of 29 scalar andiomagnetotellurlc (AMT) soundings covering the spectral frequency range 1-5000 Hz were carried out. Results from 1D modelling using both Bostick-Niblett transformation and Occam inversion show a basin-like shape of the sediment-basement interface.The AMT maximum depth of this interface is approximately at the centre of the depression and lies between 450 m and 500m.