O registro de petrotramas do granito moderna e dos granitos adjacentes, São Luiz do Anauá, Roraima

Abstract

Several Paleoproterozoic A-type granite bodies intrude the Guiana shield in the Amazonian craton, among them, Moderna granite (1.81 Ga), located between São Luiz do Anauá city and Moderna village, in the southeast of Roraima state. Magnetic anisotropy analyzes (AMS, IRM and thermomagnetic) combined with field and microstructural focus petrographic data, were used to identify the field of stresses during the Moderna granite emplacement and correlate it with regional tectonics. The monzogranite with variations for syenogranite Moderna, presents NW-SE elongation in the contact zone between the calc-alkaline Martins Pereira (1.96 Ga) and Caroebe (1.89 Ga) granites, in transitional contact with these units, marked by hydrothermal alteration features, which do not affect the orientation of the rock's magmatic fabric and is responsible for its characteristic red color, associated with plastic deformation. The magnetic fabric, marked by magnetite, and magmatic fabric orientations of the three analyzed rock units have genetic equivalence and main direction around the E-W to NE-SW axis, in agreement with the regional structural framework that controls the Orosirian plutons emplacement in the central portion of the Guiana shield. Although there is a great difference in age, reported in the literature, between the crystallization of the granite units analyzed, these rocks developed minerals fabrics with similar orientation and strain mechanisms, indicating that the granite emplacements occurred syn-kinematicly under a dextral transpressive tectonic regime with plastic strain. Localized shear zones, sub-parallel to magmatic foliation orientation, demonstrate the persistence of the effort field at the end of the plutonic housing, while discrete posterior shear zones, NW-SE direction, deform restricted portions of the rock units in solid state.