Abstract The Itabira Iron District, located at the northeastern end of the Iron Quadrangle, still presents some uncertainties regarding the tectonic origin of its macrostructure. The Itabira synclinorium is characterized by a large synformal structure in the NE-SW direction, with anticlines and synclines distributed "en echelon". The analysis of the relationship between the primary structures and the plane-axial schistosity, linear and planar structures, allowed the development of a three-dimensional model for the region. The increase in deformation from E to W, observed from the Cauê mine to the Conceição mine, and the rotation of the axes of the macrostructural folds, characterized by the Cauê, Dois Córregos, and Conceição synclines, are explained in this study by a model with six deformation phases. The increase in shortening from the Cauê mine towards the Conceição mine can be explained based on the flanking fold model. The application of this mechanism to explain kilometric-scale folding has been presented for the eastern flank of the Santa Rita Syncline in the Iron Quadrangle.

ResumoO presente trabalho se concentra na aba leste do sinclinal Santa Rita, (Dorr 1969), a partir da região conhecida como Fábrica Nova. Importantes depósitos de minérios de ferro estão localizados nos flancos dessa estrutura, como os de Timbopeba, Alegria, São Luiz, Tamanduá, Almas e Fábrica Nova. Esse sinclinal é uma dobra de escala sub-regional de direção axial N-S com raízes no embasamento adjacente do Complexo Santa Bárbara e seccionada pela falha de Água Quente. A investigação propõe a hipótese de que o arcabouço estrutural da região é resultante da superposição de pelo menos três fases de deformação sobre a nappe Ouro Preto. A mina de Fábrica Nova, localizada na porção central da área estudada, está inserida em uma estrutura sinformal de eixo 100/20, o sinforme de Fábrica Nova. Para a geometria particular dessa região, é proposto um modelo com base no mecanismo de dobramento por Flanking Folds (Passchier 2001). Esse mecanismo se daria através de um encurtamento crustal de direção E-W da fase de deformação F4.

AbstractThis study focuses on the eastern flank of the Santa Rita syncline (Dorr 1969), with specific emphasis on the region known as Fábrica Nova. Important iron ore deposits are located on the flanks of this structure, such as Timbopeba, Alegria, São Luiz, Tamanduá, Almas and Fábrica Nova. The Santa Rita syncline is a fold with N-S axial direction and of subregional scale, with roots in the adjacent basement of the Santa Bárbara Complex and sectioned by the Água Quente thrust fault. The hypothesis of this study is that the structural framework of the region resulted from the superposition of at least three deformation phases on the Ouro Preto nappe. The Fábrica Nova mine, located in the central portion of the study area, is embedded in a synformal structure with a 100/20 trending axis named Fábrica Nova synform. The proposed model to explain the particular structural geometry of this region is based on the flanking folding mechanism (Passchier 2001). This mechanism may have been developed by E-W crustal shortening during the F4 tectonic deformation phase.