U-Pb zircon and Sm-Nd geochronology of the dom Silverio group, SE Brazil: Implications for the evolution of the superposed Araçuai and Minas-Bahia orogens

The Aracuai orogen, the South American portion of the Brasiliano/Pan-African Aracuai-West Congo orogenic system (AWCO), formed during the EdiacaranCambrian assembly of West-Gondwana. The basement of a substantial portion of the Aracuai orogen comprises Archean and Paleoproterozoic rocks involved in the 2.1-2.0 Ga Minas-Bahia orogen. The Dom Silverio Group, which consists of mica schists containing layers and lenses of mafic, ultramafic, and Mn-rich rocks, as well as quartzites, graphite schists, marbles, and banded iron formations, defines a ca. 10 km-wide and 150 km-long belt in the southwestern portion of the Aracuai orogen. This succession, currently interpreted as deep marine deposits or an ocean-floor assemblage of uncertain age- Paleoproterozoic or Neoproterozoic-, potentially records processes involved in critical evolutionary stages of the superposed Minas-Bahia and Aracuai orogens. Aiming to characterize the age and tectonic significance of the Dom Silverio Group, we performed a geochronological and geochemical investigation on samples collected from selected lithotypes. U-Pb (LA-ICPMS) determinations on detrital zircons revealed two distinct age spectra. Zircons extracted from the lower Dom Silverio schists define a spectrum characterized predominantly by Neoproterozoic age clusters with a maximum depositional age of 601 +/- 10 Ma. Quartzites from the lower and upper sections of the group do not contain zircons younger than 1.9 Ga and show unimodal age distributions around 2067 Ma. The maximum depositional age estimated for these rocks is 2020 +/- 6 Ma. The spectrum of the lower section schist indicates the turbidites of the Ediacaran Salinas Formation as their most probable correlative. In contrast, the quartzites and schists of lower and upper sections correlate with the Orosirian Itacolomi Group, the post-collisional assembly of the Minas-Bahia orogen. Sm-Nd isotope analyses and whole-rock geochemistry allow the discrimination of two generations of mafic rocks. The older generation, showing TDM model ages = 1.92 to 3.6 Ga and epsilon(Nd(t)) =-12.93 to +4.63, represents components of the basement. The younger generation, with TDM model ages = 1.0 Ga to 1.25 Ga and epsilon(Nd(t)) = +0.05 to +2.29, is similar to the ophiolitic rocks that occur imbricated with Ediacaran metasedimentary successions in the central portion of the Aracuai orogen defining the Ribeirao o da Folha accretionary belt. They show Th/Yb and Nb/Yb ratios of the EMORB-OIB mantle array and Nb/Y and Zr/Y ratios compatible with OIB and oceanic plateau basalts. The Dom Silverio Group is thus a complex that involves members of the Aracuai and Minas-Bahia orogens. Their Ediacaran components materialize the southern extension of the Ribeirao o da Folha accretionary wedge and, as such, provide further evidence for oceanic consumption during the development of the southern Aracuai orogen.