O Grupo Sabara no Sinclinal Dom Bosco, Quadrilatero Ferrifero: uma revisão estratigráfica

Abstract

THE SABARA GROUP IN DOM BOSCO SYNCLINE, QUADRILATERO FERRIFERO: A STRATIGRAPHIC REVIEW The Sabara Group represents a Paleoproterozo ic metavolcanic and metasedimentary sequence that lies on top of the Minas Supergroup, the most important Paleoproterozoic sequence of the Quadrilatero Ferrifero in Minas Gerais. Although firstly defined as Sabara Formation (Gair 1958) some authors have suggest to rank the Sabara rocks as a Group, due to the expressive thickness of the sedimentary and volcanic pile, especially in the Ouro Preto area (southeast Quadrilatero Ferrifero) and in the Sabara area (northwest Quadrilatero Ferrifero). Our data support a stratigraphic division of the Sabara rocks into two formations: the basal Saramenha Formation and the Estrada Real, herein proposed. The Sabara Group is still considered to be undivided in some areas in which these two units can not be recognized or do not crop out. The Saramenha Formation consists of metadiamictites, metaritmites, metapelites, schists (mostly chlorite- schists), phyllites and lenses of dolomite. The unit is correlated to the typical Sabara Formation rocks in the Ouro Preto area. The Estrada Real Formation is represented by sandstones, metaconglomerates, metadiamictites and thin layers of iron formation. Previous contributions had considered those rocks to be part of the Itacolomi Group, the youngermost Precambrian lithostratigraphic unit of the Quadrilatero Ferrifero. The Itacolomi Group is mostly composed by impure metasandstone and grain supported metaconglomerates which overlie the Sabara rocks in erosional and angular unconformity. Several other isolated quartzite massifs are correlated to the Itacolomi Group, and include the quartzites of Chapada-Lavras Novas region (southeastern Quadrilatero Ferrifero), the quartzites of the Pires range, next to Congonhas, in the Southwest, the Frazao peak in the east and the Ouro Branco range in the south. However, the structural data collected in quartzites in all these areas are similar to the structural data presented by the Sabara Group, according to our collected structural data. The lack of reliable geochronological data, together with the herein proposed structural correlations as well as some observed contact relationships, support the lithostratigraphic correlation of such isolated quartzite massifs to the Estrada Real Formation.