A Serra das Cambotas: terminação Meridional do Supergrupo Espinhaço no Quadrilátero Ferrífero, MG

Abstract

The stratigraphic positioning of rocks grouped as Cambotas Formation (Quadrilátero Ferrífero, southeast of São Francisco Craton) has been the subject of discussion since its characterization in the 1960s. Our study provides structural and stratigraphic data of the Cambotas Formation, obtained in its type-section along with the Tamanduá and Cambotas mountain ranges, with the aim of defining the stratigraphic-temporal relationships that characterize the Cambotas Formation and its surroundings. Also presents isotopic data (U-Pb in LA-ICP-MS) intended to shed light on the age of the unit, The large shear zone systems already described in the literature were observed, as well as the textural and sedimentological characteristics. The Cambotas Formation corresponds to a unit that groups together orthoquartzites and arcosian quartzites, whose basic stratigraphic relationship is controlled by tectonic contacts, through the Fundão-Cambotas Shear Zone System, and by the Córrego do Garimpo Fault. For provenance via U-Pb isotopic analysis in LA-ICPMS of detrital zircon grains, a sample collected from the Cambotas Formation in its type-section, in the homonymous mountain range, corresponding to fine-grained orthoquartzite, in which 210-zircon grains collected and analyzed. The results indicate maximum sedimentation age during the Statherian, around 1755 ± 71 Ma, the peaks of ages between 1923 and 3010 Ma indicates a significant contribution of Paleoproterozoic to Neoarquean sources. In the light of current stratigraphic knowledge, the peak of concordant analyzes with Statherian age (~ 1.7 Ga) discards the correlation between the Cambotas Formation and the Minas or Rio das Velhas supergroups. With this, we propose that the Cambotas Formation configure the southern termination of the Espinhaço Supergroup, corresponding to a restricted basin, with a multiplicity of source areas. This variety relates to the structural and stratigraphic complexity to which the northeastern region of the current Quadrilátero Ferrífero was subjected during its genesis. The sample provides an age similar to other works in the same area, validating the stratigraphic proposals presented.

Keywords: Cambotas Formation, Quadrilátero Ferrífero¸ U-Pb Geochronology.