Gr?os detríticos de zirc?o do Grupo Itacolomi em sua área tipo, Quadrilátero Ferrífero, Minas Gerais: idades, proveniência e significado tect?nico

摘要

The Itacolomi Group in its type area, the homonymous ridge located in the southeastern portion of Quadrilátero Ferrífero mineral province in State Minas Gerais, is made up of a succession of metasandstones, metaconglomerates and phyllites, interpreted as fluvial to alluvial fan deposits accumulated in post-orogenic intermontane basins. In the type locality, the group is exposed in the form of a basal autochthonous package that unconformably overlies the 2.6-2.1 Ga Minas Supergroup, and an allochthonous block bounded by thrust faults. The c. 400m-thick autochthonous succession is weakly deformed and composed of metasandstones and metaconglomerates. Exposed in the Itacolomi Peak, the 145 m-thick finegrained metasandstones of the thrust sheet are intensively deformed. The detrital zircon age spectra obtained from these packages are slightly different. The spectra of the basal autochthonous package are clearly unimodal with age peaks at 2167, 2197 and 2203 Ma, whereas the age distributions of the upper thrust sheet are bimodal with peaks at 2156 and 2201 Ma. They indicated that the group was sourced essentially by the Paleoproterozoic arc-related granitoids of the Mineiro belt and Mantiqueira Complex, exposed respectively to the southwest and east of the Itacolomi ridge. The maximum deposition age of the group can be estimated at 2129 ± 11 Ma. These results confirm the post-orogenic nature of the Itacolomi succession, which accumulated in a back-arc/foreland setting in respect to the Paleoproterozoic orogen exposed in the Quadrilátero Ferrífero and adjacent areas.