Structural framework of the iron district of Itabira, Iron Quadrangle, Minas Gerais

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.摘要 位于四角铁矿区（Iron Quadrangle）东北端的伊塔比拉铁矿区（Itabira Iron District），其宏观构造的成因目前仍存在诸多不确定性。伊塔比拉复向斜（Itabira synclinorium）以NE-SW向的大型向斜构造为典型特征，伴生背斜与向斜呈“雁列状（en echelon）”展布。研究通过解析原生构造与轴面片理、线性及面状构造间的关联，构建了该区域的三维构造模型。本次研究观测到，从考埃矿（Cauê mine）至康塞桑矿（Conceição mine），变形程度自东向西逐渐增强，且以考埃向斜、多伊斯科雷吉斯向斜与康塞桑向斜为代表的宏观构造褶皱轴发生旋转；上述现象可通过六期变形模型予以解释。考埃矿向康塞桑矿方向的构造缩短量逐步增大这一特征，可依托侧翼褶皱模型（flanking fold model）进行阐释。将该机制用于解释千米级褶皱的研究案例，此前已见于四角铁矿区圣丽塔向斜（Santa Rita Syncline）东翼的相关研究中。