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Combined Sm-Nd isotope studies and U-Pb ages of detrital zircons have shown significant differences between the provenance patterns of Neoproterozoic metasedimentary successions in the Southern Brasília belt. The Vazante and Canastra groups are passive margin deposits with source areas in the Archean/Paleoproterozoic São Francisco Craton basement and Mesoproterozoic cover units. In literature, the younging trend of Nd model ages observed in the Vazante Group is interpreted as resulting from the contribution of the Neoproterozoic Goiás Magmatic Arc. Also, detrital zircons younger than 0.90 Ga were not recorded in the Vazante or Canastra groups, which zircon populations are older than 0.93 Ga. This work presents new Sm-Nd and Sr isotope data of metasedimentary rocks from the Vazante and Canastra groups, collected in a 400 km2 area in northwest Minas Gerais, Brazil. The improved database of previously published and new data corroborates with the younging pattern of TDM along the Vazante Group. Isochronic diagrams show that samples from Vazante and Canastra groups scatter along mixing lines between the fields defined by the older cratonic rocks and the more juvenile ones. Here we present the Tonian Intraplate Magmatism within the São Francisco Craton as the juvenile source. [ABSTRACT FROM AUTHOR]

This work presents the first Sm–Nd and Sr isotope TIMS data on the fine-grained fraction (<74 μm) of iron-rich deposits related to the November 5th, 2015 Mariana accident, caused by the rupture of the Fundão dam, an iron tailings pond operated by SAMARCO Mining. The failure of the Fundão dam provoked the gravitational flow of approximately 62 Mi m3 of a quartz and iron oxide-rich slurry composed of water, fine sand and silt, that flowed into the Gualaxo do Norte and Carmo rivers, and eventually along the whole Doce River. Samples were collected between 5 and 80 km downstream from the Fundão Dam, along the Santarém creek and the Gualaxo do Norte and Carmo rivers. XRD analyses show that samples are >90% composed of quartz and iron oxides (hematite, goethite and magnetite), with minor phyllosilicates (kaolinite and mica). Owing to sediment transport processes, heavy (hematite, goethite, magnetite) to light (quartz, phyllosilicates) mineral fractionation is observed. As with XRD data, major and trace element compositions also closely match those of the original Paleoproterozoic Cauê Formation BIF iron ore. The studied samples yielded δ Nd between −17.0 and −19.7 pptt (part per ten thousand), with the exception of one sample, with δ Nd of −23.2 pptt. Strontium 87Sr/86Sr ratios show variability between 0.7351 and 0.7729. The T DM ages scatter between 1.94 Ga and 2.75 Ga, with a negative correlation with phyllosilicate contents, indicating that the latter has preferential provenance from younger, more juvenile sources than the Cauê Fm itabirites. This interpretation is corroborated by two component mixing models of Nd and Sr isotope ratios, where the Nd–Sr isotopic signatures of the studied samples are compatible with >98% of the Cauê Fm itabirite component, mixed with a Neoproterozoic juvenile mafic rocks component, such as those from the ophiolitic assemblages of the distal Macaúbas Group, or tholeiitic mafic rocks of the Pedro Lessa suite. The reported Sm–Nd and Sr isotope compositions closely match those of the original iron ore and contrast with either those of the upriver or downriver Precambrian to Ordovician bedrock units. The firstly defined isotope signature can thus be potentially used as a proxy for ongoing suspended sediment dispersion studies farther downstream along the Doce River and in adjacent marine environment. Image 1 • First Sm-Nd and Sr isotope composition of proximal iron-rich sediment from the Mariana mining accident of November 2015. • Sm–Nd and Sr isotope composition is controlled by phyllosilicate mineral content, which tends to decrease downstream. • Sm-Nd and Sr isotope compositions match those of iron ore and contrast with those of the upriver or downriver bedrock units. • The firstly published signature is a proxy to sediment dispersion downstream along the Doce River and adjacent marine system. [ABSTRACT FROM AUTHOR]

New petrography, geochemistry and Sm-Nd and Sr data from the orthogranulites of the Juiz de Fora complex in southern Rio de Janeiro State and compiled information provide insights on the petrogenetic and tectonic evolution. The complex comprises several geochemical groups including mafic orthogranulites (three tholeiitic and one alkaline) and felsic orthogranulites (three calc-alkaline and one tholeiitic/low K calc-alkaline). New geochemical and isotope data, combined with available U-Pb data suggest a long evolutionary history from the Paleoproterozoic to the Neoproterozoic. The oldest magmatic episode produced juvenile to slightly contaminated arc-type Rhyacian rocks, as well as granitic rocks related to collision or post-collision episodes. Altogether these rocks integrate part of a dismembered Rhyacian orogen within the Ribeira belt. Few TDM Nd model ages yielded 2.75 to 2.58 Ga, suggesting minor Archean contribution for magma genesis. Some of the basic granulites' bodies yield Meso-to Neoproterozoic TDM Nd model ages, which may refer to an extensional magmatism. Orthogranulites present granulite facies paragenesis, related to the youngest tectonic episode in the Juiz de Fora Complex (Brasiliano Orogeny). The new data are potentially important for Paleoproterozoic reconstruction models, due to the predominantly juvenile character of the Juiz de Fora complex, as similarly worldwide. [ABSTRACT FROM AUTHOR]

Sedimentary provenance analysis based on lithogeochemistry and isotope data has been extensively applied in the investigation of ancient sedimentary successions. This approach contributes to understand the tectonic setting in which these strata were deposited and to recognize major provenance patterns in time and space. The Ediacaran to Cambrian Bambuí Group is exposed in the São Francisco craton (SE Brazil) and represents the sedimentary record of a foreland basin system developed during the assembly of the West Gondwana. Different lines of evidence indicate that this basin system evolved into a confined setting, due to the overloads imposed on the western and eastern margins of the São Francisco paleoplate by the diachronic Brasília and Araçuaí orogenic systems, respectively. New whole-rock lithogeochemistry and Sm–Nd isotopic data were applied to evaluate the overall sedimentary provenance patterns of the Bambuí strata exposed in the southern portion of the São Francisco craton (i.e., within the Sete Lagoas basement high) and to identify its possible sources. Coupled (La/Yb) n and Th/Sc ratios with 147Sm/144Nd and εNd isotopes allowed the recognition of three contrasting source patterns associated with different 2nd order sequences. The lower sequence comprises carbonate ramp deposits and shows highly heterogeneous and more negative εNd ranging from −10.5 to −4.5, as well as Th/Sc and (La/Yb) n ratios between 0.6 and 0.7 and 0.54 and 0.76, respectively. The provenance patterns point toward intermediate-dominated and isotopically evolved crustal sources, with mean T DM model ages between 1.5 and 2.0 Ga. The overlying 2nd-order sequence is composed of fine-to medium-grained siliciclastics grading upward into platformal oolitic calcarenites and calcilutites. This succession exhibits homogeneous and less negative εNd (t) values between −6.8 and −5.2, with low Th/Sc (0.6–0.8) and (La/Yb) n (0.60–0.84) ratios. The uppermost Bambuí 2nd-order sequence, marked by greenish siltstones and arkoses grading upward into storm-bedded arkoses and lithic sandstones, shows homogeneous εNd (t) ranging from −8.5 to −6.1, slightly more negative than the underlying successions, and relatively higher Th/Sc and (La/Yb) n ratios ranging from 0.7 to 1.3 and 0.85 to 1.28, respectively. The Sm–Nd isotopic signature of the upper deposits indicates felsic-dominated and more isotopically juvenile crustal sources with T DM model ages of 1.5–1.7 Ga , characteristics compatible with Ediacaran arc-related rocks and post-tectonic granites exposed in the Araçuaí orogen. Our data indicate that the Proterozoic cratonic covers, their correlatives in the surrounding orogens, and magmatic rocks from the Araçuaí orogen acted as major sedimentary sources during the first evolutionary stages of the Bambuí basin-cycle in the Sete Lagoas basement high, which behaved as a forebulge depocenter. During the deposition of the overlying sequences, the Araçuaí orogen rocks became increasingly important in sourcing the Ediacaran- Cambrian foreland system in this depocenter. Besides revealing the major provenance patterns through the evolution of an ancient and partially confined foreland basin system, our data also demonstrates that even minor changes in the Sm–Nd system might be useful as reliable elements on the provenance analysis of sedimentary systems elsewhere. [Display omitted] • Sm–Nd isotopes and trace elements are used as provenance proxies in the Bambuí Group. • Felsic vs. mafic and juvenile vs crustal provenance changes are revealed along stratigraphy. • Geochemical and isotopic variations are related to tectonic activity in adjacent orogenic belts. [ABSTRACT FROM AUTHOR]