A MAGNETOTELLURIC INVESTIGATION OF THE ARAGUAINHA IMPACT STRUCTURE INMATO GROSSO-GOIAS, CENTRAL BRAZIL

With a diameter of 40 km the Araguainha Dome is the largest known impa ct site in South America. The main characteristics of the structure is its appearance as a set of imbricated circles and a central uplift wi th a diameter of 9 km. 25 magnetotelluric (MT) soundings were complete d across the structure, approximately defining five radial sections. T he MT responses in the frequency range from 1000 to 1 Hz show 1-D beha viour, in contrast to the longer periods where data indicate a strong anisotropy and a decline of the resistivity. 1-D modelling of the high -frequency data reveals a well-defined symmetric crystalline basement ring at 1000 m depth between the radii of 9 and 20 km, which seems to drop deeper further away from the centre. Inside the ring and toward t he centre, the top of the granites rises, outcropping at 1.5 to 2 km f rom the centre.