THE THRUST CONTACT BETWEEN THE CANASTRA AND VAZANTE GROUPS IN THE SOUTHERN BRASILIA BELT: STRUCTURAL EVOLUTION, WHITE MICA CRYSTALINITY AND IMPLICATIONS FOR THE BRASILIANO OROGENY

CLAUDIO DE MORISSON VALERIANO; AGNES IMPICCINI; MANUELA DE OLIVEIRA CARVALHO1; GUSTAVO DINIZ OLIVEIRA; PAMELA ALEJANDRA APARICIO GONZÁLEZ

Brazilian Journal of Geology

Zeppelini

Año: 2016 vol. 46 p. 567 - 583

Two regional thrust-sheets of Neoproterozoic metasedimentary rocks occur in the southern Brasilia belt, northwest Minas Gerais. The lower one comprises the Vazante Group, that is formed in the studied area, from base to top, by the Serra do Garrote (metapelites interlayered with carbonaceous phyllite), Serra do Poço Verde (beige to pink stromatolitic metadolomite with interlayered greenish slates), Morro do Calcário (gray stromatolitic metadolomite interlayered with gray slates) and Serra da Lapa (phyllite with dolarenitic lenses interlayered with slates) formations. The upper thrust sheet consists of the Canastra Group (Paracatu Formation): laminated sericite phyllites and carbonaceous phyllites interlayered with quartzite. The Braziliano orogeny resulted in four phases of compressive deformation, associated to low grade metamorphism. The first two (D1, D2) are ductile while the third and fourth ones (D3 and D4) are brittle-ductile. D1 developed a slatyS1 cleavage subparallel to the primary layering, with shallow to steep dips to NW. D2 developed crenulation cleavage associated with tight to isoclinal folds. D3 and D4 phases developed crenulations and open folds and kink bands. S3 dips steeply to NW, while S4 has moderate to steep dips to NE and SW. White mica crystallinity (Kübler index) measurements in metapelites indicate that both the Canastra and Vazante groups reached anchizone/epizone conditions, and metamorphic discontinuities along thrust planes indicate that the peak of metamorphism pre-dated thrust tectonics.