Lucia Castanheira de Moraes

Within plate, arc, and collisional Neoproterozoic granitic magmatism in the Araxá Group, Southern Brasília belt, Minas Gerais, Brazil

Three Neoproterozoic granitic episodes associated with the Araxa Group, in Southern Brasilia Belt between the cities of Araxa and Cascalho Rico, Minas Gerais State, Brazil, are characterized from the geologic, geochemical, and geochronological points of view. The earliest episode, of 833 Ma, generated in a within-plate environment, is represented by the Quebra Anzol Granite, which has: low 87 Sr/ 86 Sr = 0.706 ratios and e Nd(833) = -3.98; high levels of SiO 2 , Na 2 O, MnO, Nb, Y and Co; and low concentrations of Sr and Ba, with the absence of anorthite and presence of diopside, acmite, and positive Eu anomaly, therefore it may have been originated from mantle sources with small crustal contamination. The second episode, of 790 Ma, is represented by the pre-collisional Monte Carmelo Granitic Complex, which was partially remobilized in a collisional event around 630 Ma. It is metaluminous to peraluminous with low 87 Sr/ 86 Sr ratios of 0.706, high light rare earth elements fractionation relative to heavy rare earth elements, and negative Nb, Ta, Sr, P, and Ti anomalies. Their e Nd(790) = -2.218, with T DM = 1.29 Ga, indicate an origin from juvenile sources and reveal the existence of a late Mesoproterozoic magmatic arc in this region. The last granitic episode has taken place in a collisional tectonic environment between 642 and 630 Ma, generating peraluminous granites with muscovite, garnet, and tourmaline denominated Serra Velha, Tamandua, Pirapetinga, Galheirinho, Perdizes, Estrela do Sul, and Cascalho Rico. They have negative e Ndt , Nd model ages from Neo to Mesoproterozoic, and variable rare Earth elements enrichment patterns, with strong negative Eu anomalies.

Geology, geochemistry and petrology of basalts from Paraná Continental Magmatic Province in the Araguari, Uberlândia, Uberaba and Sacramento regions, Minas Gerais state, Brazil

This study covers the region between the cities of Sacramento and Araguari/Uberlândia (Minas Gerais State, Brazil), where basalt flows from the Parana Continental Magmatic Province outcrop. The investigated rocks present tholeiitic signature, with high titanium content, and are classified as Pitanga magma-type. The preserved basalt thickness is between 10 and 200 meters and individual flows do not exceed 15 meters thick. Flows were identified as sheet lobes, smaller and thinner flows units — stacked laterally and vertically forming compound lavas —, or frontal, centimetric lobes. The basalt flows show decimetric to metric intercalations of clastic sedimentary rock, with depositional characteristics that can vary from aeolian to lacustrine, and are important markers on prevailing environmental conditions. The plagioclases are dominantly labradorite and pyroxene is augite, whereas olivine can be hyalosiderite or hortonolite/ferrohortonolite. The behavior of the major, minor and trace elements is compatible with the presence of at least two parental magmas, which were subjected to fractional crystallization mainly of plagioclase, clinopyroxene, ilmenite and magnetite. There is a chemistry distinction between basalts from Sacramento to those from Araguari/Uberlândia region, the former one showing more evolved than the last one. The high (La/Lu)N values are indicative of partial melting of a garnet peridotite, while the Rare Earth Elements (REE) values are indicative of fractional crystallization.

Geochemistry of basaltic flows from a basalt ring structure of the Serra Geral formation at Água Vermelha dam, Triângulo Mineiro, Brazil: implications for the magmatic evolution of the Paraná-Etendeka Province

The Serra Geral Formation belongs to the Parana-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 Agua 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 Agua Vermelha are important to comprehend the evolution of the PEMP.

Geoquímica e proveniência sedimentar da Formação Uberaba (sudeste do Triângulo Mineiro, MG)

Manuscript ID: 20170032. Received in: 01/12/2017. Approved in: 04/26/2017. RESUMO: A Formação Uberaba, de idade campaniana e ocorrência restrita à região da cidade homônima, é composta de arenitos líticos e conglomerados de cor esverdeada, com possível contribuição vulcanoclástica. Nessa unidade ocorrem minerais pesados como ilmenita, granada, perovskita e magnetita, além de clinopiroxênio, plagioclásio, quartzo, calcita e apatita. A Formação Uberaba é marcada geoquimicamente por altos teores em Ba, Ta, La, Nb e Th, com padrões de elementos terras raras normalizados ao condrito fortemente fracionados (LaN/YbN = ca. 128) e planos (sem anomalia de Eu). Análises de química mineral das granadas detríticas da Formação Uberaba indicam predominância de chorlomita com afinidade com granadas crustais (G3). A proveniência sedimentar da Formação Uberaba corresponde a uma mistura de materiais de distritos alcalinos do Alto Paranaíba e derivados da erosão da Formação Serra Geral e dos grupos Canastra e Araxá. Os conglomerados produtores de diamante que ocorrem proximamente, em Romaria, foram considerados por alguns autores como correlatos à Formação Uberaba, porém a composição das granadas retiradas desses conglomerados é bastante diferente, plotando no campo de granadas mantélicas (G9/G10). Descarta-se, dessa forma, correlação entre essas duas unidades, e a Formação Uberaba, portanto, não é uma fonte provável dos diamantes aluvionares encontrados no rio homônimo.