Neoproterozoic glacial deposits from the Araçuaí orogen, Brazil : age, provenance and correlations with the São Francisco craton and West Congo belt.

Abstract

Glacigenic diamictite successions of the Macaúbas Group are widespread in the western domain of the Araçuaí orogen, east of the São Francisco craton (Brazil). Diamictites also occur on this craton and in the African counterpart of the Araçuaí orogen, theWest Congo belt. Detrital zircon grains fromthe matrix of diamictites and sandstones from the Macaúbas Group were dated by the U–Pb SHRIMP technique. The geochronological study sets the maximum depositional age of the glacial diamictites at 900 Ma, and indicates multiple sources for the Macaúbas basin with ages ranging from 900 to 2800Ma. Sm–Nd TDM model ages, determined on whole rock samples, range from 1.8 Ga to 2.5 Ga and get older up-section. Comparison of our data with those from the cratonic area suggest that these glacial deposits can be correlated to the Jequitaí and Carrancas diamictites in the São Francisco craton, and to the Lower Mixtite Formation of the West Congolian Group, exposed in Africa. The 900–1000 Ma source is most probably represented by the Zadinian–Mayumbian volcanic rocks and related granites from the West Congo belt. However, one of the most voluminous sources, with ages in the 1.1–1.3 Ga interval, has not been detected in the São Francisco-Congo craton. Possible sources for these grains could occur elsewhere in Africa, or possibly from within the Brasília Belt in western central Brazil.