UPPER CRUSTAL STRUCTURE OF THE NORTHEAST PARANA BASIN, BRAZIL, DETERMINED FROM INTEGRATED MAGNETOTELLURIC AND GRAVITY MEASUREMENTS

Eight magnetotelluric (MT) soundings were performed as a continuation of an earlier audiomagnetotelluric (AMT) survey conducted in the northeastern border of the Parana basin, a large intracratonic basin located in central eastern South America and constituted by Silurian to Jurassic sedimentary rocks with Lower Cretaceous sill-type magmatic intrusions and overlying volcanics. Two of the MT station, were carried out near two deep petroleum wells. The remaining MT soundings were done on a profile traversing two important gravity features: a positive anomaly near the border of the states of Sao Paulo and Minas Gerais and a strong (trending NW-SE) linear gradient. Major findings of an integrated interpretation of the MT survey and of available gravity data are as follows: (1) inhomogeneities and/or strong magnetization of the superficial volcanics and diabase intrusions in the Paleozoic sedimentary rock's appearing to distort the MT results; and (2) identification of important structural discontinuities, including a possible different crustal structure beneath the Parana basin compared to the region on the north, a thickening of the crust toward the NE, and the probable existence of a trough (graben?) within the basin, characterized by a thick accumulation of sediments and basalts.