O arcabouço estrutural da região de Chega-tudo e Cedral, noroeste do Maranhão, com base em sensores geofísicos

The central-northern continental segment of the Brazilian coast, which straddles the boundary between the Pará and Maranhão States, is known in the geological literature as the Gurupi Region. The region is characterized by the presence of two main erosional Precambrian windows which expose small-sized Proterozoic shields in Phanerozoic sedimentary basins. Advances in the understanding of the Precambrian geological history of this area have been limited by the lack and quality of exposures due to the deep weathering profile developed. The use of airborne geophysics proved to be a helpful tool allowing a better definition of some lithological contacts and the shape of major tectonic features. The study area covers part part of the Gurupi Shear Belt, located in one of the Precambrian windows mentioned. This segment of the belt exhibits a variety of sedimentary- and igneous-derived supracrustal rocks in association with plutonic-derived metamorphic rocks. These rocks are structurally organized in three main NW-trending strips which were correlated to the Maracaçumé Complex, Gurupi Group and Tromai Suite. Sheared- and hydrothermally-altered basic and ultrabasic intrusive rocks are often found tectonically interlayered with the Gurupi Group rocks. All the above-mentioned rocks have been metamorphozed under low green-schist to low amphibolite facies conditions and affected by hydrothermal alteration. Diabase dikes crosscut the main Precambrian lithological units along several structural trends. Alluvial deposits along active drainages constitute the youngest lithologic units in the area. The kinematic and geometric analysis of the main tectonic structures observed allows the definition of the area as a shear-belt segment, characterized by steeply-dipping planar structures which are indicative of an oblique left-hand continental collision. The area is also characterized by the presence of a relatively narrow NW-trending highlystrained zone developed along carbonaceous metapelitic lithologic units. This corridor is well ...