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Título

The Espinhaço Supergroup in the Southern Espinhaço Front: new detrital zircon U-PB ages and statistical analyses from the region of Serra do Cipó, Minas Gerais

Texto do resumo

In the region of Serra do Cipó, the homonymous range is a segment of the Southern Espinhaço Range (SER), a fold-and-thrust belt marking the limit between the Araçuaí Orogen and the São Francisco Craton. To clarify local stratigraphic issues, we performed statistical analyses on new and compiled detrital zircon U-Pb ages from the SER and adjacent regions. The new data come from representative samples from the study area, formerly classified into the Espinhaço Supergroup or the Macaúbas Group. In addition to these results, we compiled available detrital zircon U-Pb ages from studies addressing the various individual formations of the Espinhaço Supergroup (Mesoproterozoic) and the Macaúbas Group (Neoproterozoic), as well as the Costa Sena Group (Paleoproterozoic) and the Jequitaí Formation (Neoproterozoic), all previously suggested as candidate classification options for the local rocks or found in the vicinities of the study area. All data – from our samples and compiled – were evaluated by Kernel Probability Density (KPD) distributions, cumulative frequency charts and Kolmogorov-Smirnov tests, the former complemented by Multidimensional Scaling (MDS) for visual representation. Based on the resulting curves, test results and scatter diagrams, three sets are clearly distinguishable: i) samples from the Barão do Guaicuí and Meloso formations (the Costa Sena Affiliation Group); ii) samples from the base of the Espinhaço Supergroup up to the Sant Rita Formation (the Espinhaço Affiliation Group); and iii) samples from the remaining Upper Espinhaço Supergroup, the Macaúbas Group and the Jequitaí Formation (the Macaúbas-Jequitaí Affiliation Group). Our new data from Serra do Cipó were obtained from five siliciclastic (quartzites and metaconglomerates) samples representative of the local rocks. The detrital zircon grains are well-rounded, indicating sediment maturation during transport. From all methodological perspectives, all our samples show strong affinity with the Espinhaço Supergroup, and in particular with our Espinhaço Affiliation Group. The most prevalent age sets are Neoarchean (2.9-2.6 Ga) and Rhyacian-Orosirian (2.2-2.0 Ga). The maximum deposition ages indicated by the youngest zircon grains (YZG) are of Calymmian age in two samples (1581 ± 35 Ma and 1579 ± 40 Ma), Statherian in two samples (1613 ± 47 Ma and 1656 ± 26 Ma) and Orosirian in one sample (1831 ± 26 Ma). The analytical-statistical results coupled with the petrographic features and faciological associations observed in the context of each sample suggest correlation of the local outcropping units with the São João da Chapada, Sopa-Brumadinho, Galho do Miguel and Santa Rita formations of the Espinhaço Supergroup. The data do not support the presence of pre-Espinhaço units in the region of Serra do Cipó. Even though the YZG criterion does not preclude the presence of the younger Macaúbas Group and Jequitaí Formation in the study area, the detrital zircon age spectra obtained for our samples are significantly dissimilar to the regional detrital ages from these units. Especially, Sthenian and Tonian detrital ages, typical of the Macaúbas Group and the Jequitaí Formation, are absent in our data. Possible source areas of zircons are Archean-Paleoproterozoic basement blocks from the region and Statherian rift suites. Likely sources of Calymmian zircons, however, remain unknown, although possible distant areas of this age exist in the Northern Espinhaço Range.

Palavras Chave

Espinhaço Supergroup; detrital zircons; U-Pb dating; geochronology; Southern Espinhaço Range