The Statherian Natividade Basin evolution constrained by U–Pb geochronology, sedimentology, and paleogeography, central Brazil

Abstract

The tectonostratigraphic evolution of the intracontinental Natividade Basin is evaluated by zircon U/Pb analysis of one sample of acidic metavolcanic rock observed at the bottom of the depositional succession and three samples of metasedimentary rocks collected at different stratigraphic levels. The metavolcanic sample yielded a 1824 Ma zircon U–Pb age, and the youngest detrital zircon grains from the metasedimentary sequence resulted in a maximum depositional age of 1776 Ma for the paleobasin. The isotopic data associated with the analysis of stratigraphy, paleogeography, and sedimentary environments converge to the interpretation that the Natividade Group evolved from the late Paleoproterozoic (Statherian), possibly entering the early Mesoproterozoic. The sedimentation is interpreted to have occurred between the deposition of the Araí and the Traíras/Serra da Mesa groups. This understanding is due to the absence of continental sediments in the Natividade Basin (which could corroborate the correlation with the Araí Basin) and the absence of detrital zircon grains younger than 1.5 Ga (which would support the correlation with the Traíras/Serra da Mesa groups). The metavolcanic rocks are observed only locally and are interpreted as the result of melting by crustal rifting that was greatest in the south, related to the Araí Group, and decreased northwards of the study region. The mechanical subsidence responsible for the deposition of the Araí Group continental sediments was not observed in the Natividade Basin. The thermo-flexural subsidence responsible for the Natividade Basin evolution allowed the deposition of complex sedimentary environments related to mixed siliciclastic platforms and shallow water turbidite facies. Based on bibliographic studies and fieldwork data, our geological model suggests that the Almas Block was possibly a high paleorelief area, separating the Araí Basin to the south and the Natividade Basin to the north. This assertion is based on the following facts for the study area: i) there is no occurrence of the Veadeiros Supergroup sediments; ii) Nowadays in the region, there are many high relief areas related to quartzite layers and several granitic units that are resistant to denudation processes; iii) deposition of the shallow water turbidite present at the Natividade Group needed elevated source areas to control the sedimentation; iv) The predominance of carbonates and mass flow deposits in the southern portion of Natividade Group, near to Almas Block, suggests a lower depth of the sea to the south of the basin. Further north, the predominance of fine-grained terrigenous deposits suggest a deeper basin; v) it is common in rift-sag environments the preservation of elevated blocks as an isostatic compensation mechanism. The integrated analysis conducted allowed the following conclusions: the Natividade Basin evolution is not coeval with the Araí or the Traíras/Serra da Mesa basins and is classified as a sag-type basin in which the sedimentary environments resulted in massive carbonate accumulation in a complex platform controlled by the basement paleorelief.