Abstract Salinas Formation occurs in a large region of the Northern Araçuaí orogen, Southeastern Brazil. It includes turbiditic wackes (> 10% matrix) to arenites (< 10% matrix), pelites and clast-supported conglomerates, metamorphosed from the biotite zone of the greenschist facies to the sillimanite zone of the amphibolite facies. Salinas Formation lies unconformably on the top of or in tectonic contact with the Macaúbas Group, and hosts Cambrian granitic intrusions dated between 540 and 500 Ma. Aiming to unravel sediment provenances for the Salinas basin, we present a detailed lithochemical (45 samples) study on low-grade rocks preserved from the regional deformation, which are found in the type area of the Salinas Formation. In addition, we compare them with deformed and more metamorphic rocks of similar composition but located in other basin sectors. The lithochemical data indicate limited chemical weathering in the sediment sources, good correlations with the mineralogical compositions in respect to the variable amounts of metamorphic minerals typical of pelitic (micas, garnet, and other peraluminous silicates) and psammitic (feldspars, quartz) fractions. The main provenances of sedimentary protoliths are clearly related to continental magmatic arc and active continental margin environments. U-Pb (SHRIMP) analyses performed on zircon grains from clasts of intermediate to felsic volcanic rocks, extracted from a clast-supported metaconglomerate, yield concordant zircon Pb 206 /U 238 ages from ca. 579 Ma to ca. 697 Ma, with most of the ages in the interval of 587 to 630 Ma. This indicates that the main primary sediment source is the Rio Doce magmatic arc (630-580 Ma), in very good agreement with the arc-related lithochemical signature. Eleven zircon crystals yield a Concordia age of 620 ± 10 Ma, representing an important Ediacaran volcanic episode in the tectonic evolution of the Araçuaí orogen.

ABSTRACT: The Espinhaço rift system encompasses taphrogenetic events from the Statherian to Tonian in the São Francisco-Congo (SFC) paleocontinent. The magmatism is represented mainly by metamorphosed anorogenic granites and rhyolites with subordinate amphibolites. Zircon U-Pb (LA-ICPMS and SHRIMP) ages from felsic (1748 ± 3 Ma and 1740 ± 8 Ma) and mafic (1725 ± 4 Ma) rock samples, coupled with previous studies suggest that the Espinhaço igneous province erupted from ca. 1.79 Ga to ca. 1.70 Ga. The felsic rocks show characteristics of A-type magmas. The negative εHf(t) data for meta-rhyolite zircons (-12.32 to -17.58), the moderate δ 18 O values (7.02 to 7.98) and the REE patterns suggest crustal melting related to an extensional environment. The mafic rock shows negative values of εHf(t) in zircons (-4.05 to -8.25) and moderate δ 18 O values (5.56 to 7.87). The results disclose a basaltic magmatism in continental intraplate setting whose parental magma could have been derived from the subcontinental lithospheric mantle with contamination of crustal material. These data coupled with coeval Espinhaço magmatism and mafic dyke swarms found to the south of the Espinhaço rift system reinforce the evidence of a long-lived Statherian silicic large igneous province (SLIP) on the SFC paleocontinental block.

ABSTRACT: The Serra Geral Formation belongs to the Paraná-Etendeka Magmatic Province (PEMP) and its geochemical and petrographic characteristics are not homogeneous. Many studies segment this group into six basaltic and two rhyolitic magma-types. It is believed that its extrusion occurred through crustal fissures in the Cretaceous, but some authors described the presence of conduits in the shape of basaltic ring structures (BRS) in the Água Vermelha region in the North of the province. The BRS rocks, based on textures and structures, were divided into four groups-central flow, basal flow, main ring dyke and lava flow-with a very similar petrography, composed of plagioclase (labradorite-bytownite), clinopyroxene (augite) and oxide (titanomagnetite) with intergranular texture. The whole-rock analyses of the basal and lava flows allow classifying them as tholeiitic basalts of the Paranapanema magma-type. Geochemical data interpretation suggests an enriched magma source, with low degree of partial melting, high depth of melt generation and without significant crustal contamination. The BRS experienced fractional crystallization on shallow magma chamber, influenced by successive new injections from different parental magmas which would be responsible for the pulses of effusion and explosion. Thus, the singularities of the BRS of Água Vermelha are important to comprehend the evolution of the PEMP.

RESUMO: Dados quimioestratigráficos de alta resolução em carbonatos da Formação Sete Lagoas (Grupo Bambuí) apresentam grandes variações nas composições isotópicas de C, O e Sr. Os calcários impuros na base da unidade mostram valores primários de δ 13C entre -1,0 e 0‰ e de δ 18O, entre -12,0 e -8,0‰. No entanto, alguns níveis de dolomitos indicam valores de δ 13C variando de +2,8 a -6,8‰ e razões 87Sr/86Sr altamente radiogênicas (>0,7111), além de baixas concentrações de Sr (<350 ppm) relacionadas a processos pós-deposicionais. Em contraste, os calcários puros no topo da unidade demonstram valores de δ 13C muito positivos entre +8,3 e +12,8‰, de δ 18O entre -10,0 e -6,0‰ e razões 87Sr/86Sr de 0,7073 a 0,7086, com altas concentrações de Sr (>900 ppm). Esses estão ligados a controles deposicionais na plataforma carbonática, tais como fluxos de água fluvial e/ou submarina, em que os carbonatos depositados no setor proximal exibem variações isotópicas de Sr significativas e os depositados no setor distal não estão sujeitos a tais controles, resultando em perfis isotópicos de Sr homogêneos. No entanto, as razões 87Sr/86Sr dos carbonatos distais são menos radiogênicas do que aquelas esperadas para o Ediacarano tardio (~0,7085). Essa discrepância sugere um ambiente deposicional em uma bacia marinha restrita, sem homogeneização isotópica de Sr com oceanos contemporâneos e, neste caso, as correlações globais baseadas na estratigrafia isotópica de Sr não são confiáveis.

ABSTRACT: High-resolution chemostratigraphic data of carbonates from the Sete Lagoas Formation (Bambuí Group) show large variations on the C, O, and Sr isotope compositions. Impure limestones at the base show primal δ13C values between -1.0 and 0‰, and δ18O values between -12.0 and -8.0‰. However, some dolostones demonstrate δ13C values varying from +2.8 to -6.8‰, highly radiogenic 87Sr/86Sr ratios (>0.7111), and low Sr concentrations (<350 ppm) related to post-depositional processes. In contrast, pure limestones at the top show very positive δ13C values between +8.3 and +12.8‰, δ18O values between -10.0 to -6.0‰, and 87Sr/86Sr ratios from 0.7073 to 0.7086, with high Sr concentrations (>900 ppm). They are linked to depositional controls on the carbonate platform, such as fluvial and/or submarine water influx, in which carbonates deposited on the proximal sector exhibit significant Sr isotopic variations and those on the distal sector were not subject to such controls, resulting in very homogeneous Sr isotope profiles. However, 87Sr/86Sr ratios of the distal carbonates are less radiogenic than carbonates expected for late Ediacaran (~0.7085). This discrepancy suggests a restricted marine basin without Sr isotopic homogenization with contemporary oceans and, in this case, global correlations based on Sr isotope stratigraphy are not reliable.