U-Pb geochronology of the 2.0 Ga Itapecerica graphite-rich supracrustal succession in the São Francisco Craton: Tectonic matches with the North China Craton and paleogeographic inferences

Abstract

LA-ICPMS U-Pb isotopic studies are conducted for key samples from the Itapecerica graphite-rich supracrustal succession and the crystalline basement in the southern São Francisco Craton (SFC). The detrital zircon analyses in paragneiss indicated a maximum deposition age of ∼2080Ma. The age spectra in the relative probability diagrams suggested the precursor basin was essentially fed with detritus from the accretionary complexes of the Mineiro belt (2470–2000Ma), which is the most preserved segment of the Minas Orogen. The basement rocks yielded zircon U-Pb crystallization ages between 2753±81 and 2679±61Ma, whereas the metamorphic overprint gave 2069±84Ma. One nearby charnockitic gneiss yielded a Sm-Nd garnet+whole rock linear array with an age of 2086±19Ma. The youngest ages estimate the timing of the regional prograde granulite facies metamorphism that also overprinted the Itapecerica rocks, given our upper intercept zircon U-Pb ages of 1997±20Ma and 1971±40Ma in paragneiss and quartzite, respectively. These ages also constrained the timing of the conversion of carbonaceous material into graphite in the Itapecerica mine – the second largest graphite mine in Brazil. The high-grade metamorphism was associated with the final docking of the Mineiro belt against the Neoarchean foreland. The Minas Orogen has geologic matches with the Jiao-Liao-Ji Orogen located in the present eastern margin of the North China Craton, where khondalites, UHT granulites, anatectic charnockites, as well as large graphite deposits are documented such as in the 1.97–1.88Ga Korean arc. The tectonic similarities between the two cratons support a relatively close position at the time frame. The dynamic scenario considers broadly coeval accretionary/collisional belts along the active margins of Archean blocks, the progressive closure of the Paleoproterozoic Ocean and final docking of the São Francisco/Congo paleocontinent against the active continental margin of the North China Craton. The work model allows new insights into the paleogeography of the core of supercontinent Columbia at ∼1.90Ga and the subsequent (1.78–1.50Ga) intraplate activity.