Upper crustal structure of the northeast Paraná Basin, Brazil, determined from integrated magnetotelluric and gravity measurements

Abstract

Eight magnetotelluric (MT) soundings were performed as a continuation of an earlier audiomagnetotelluric (AMT) survey conducted in the northeastern border of the Paraná 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 stations 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 São 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 rocks appearing to distort the MT results; and (2) identification of important structural discontinuities, including a possible different crustal structure beneath the Paraná 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.