EM - Escola de Minas
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6
Notícias
A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.
Navegar
2 resultados
Resultados da Pesquisa
Item Deciphering the source of multiple U–Pb ages and complex Hf isotope composition in zircon from post-collisional charnockite-granite associations from the Araçuaí orogen (southeastern Brazil).(2020) Melo, Marilane Gonzaga de; Lana, Cristiano de Carvalho; Stevens, Gary; Hartwig, Marcos Eduardo; Pimenta, Marcel Sarcinelli; Nalini Júnior, Hermínio AriasGiant post-collisional magmatic systems are marked by an intricate diversity of zircon ages and Hf isotopic signatures. Granites and charnockites from such systems are in high contrast with simple isotopic composition of modern granites, which often record no more than one crystallization age. Despite the complexity, the assortment in ages and isotopic compositions can be explored to extract vital information to understand magma histories, isotope fractionation and magma sources. Here we focused on a charnockite-granite association (Barra do Sao ˜ Francisco pluton - BSFP) formed during the post-collisional stage of the Araçuaí orogen (southeastern Brazil). The chemical composition of these rocks points towards a metaluminous to slightly peraluminous character, ferroan and calc-alkalic to alkalic signature. Zircons extracted from the BSFP show a large scatter in the U–Pb age distributions (from 614 to 498 Ma), indicating a complex history of magmatic processes during the wanning stages of the orogeny. Detailed discrimination analysis based on texture, chemistry and U–Pb data established well-defined age groups (groups I to III); each of which reveales a significant part of this post-collisional magmatic evolution (ca. 614-552 Ma, ca. 528-513 Ma and ca. 510-498 Ma). Zircon xenocryst cores of Group I have a broad age distribution (ca. 614-552 Ma) that mirror the age distribution within the magmatic and inherited zircon populations from the country rock (Carlos Chagas batholith). The other two age groups are present in all samples and are interpreted here as antecrysts (Group II: ca. 528-513 Ma) and autocrysts (Group III: ca. 510-498 Ma). All charnockite samples show negative εHf(t) (from − 7.4 to − 0.5) and Calymmian to Ectasian model ages (TDM = 1.58-1.21 Ga), indicating contribution from heterogenous sources. The granites exhibit more negative εHf(t) values (from − 9.3 to − 5.9) and largely older model ages (TDM = 1.68-1.49 Ga), indicating that the charnockite and granite magmas were derived from the different crustal sources. These Hf isotopes data are a robust evidence of different source rocks for these magmas with different water activities. The age of the zircon autocrysts and antecrysts can be interpreted as an evidence for a prolonged pluton assemblage probably combined with slow magma cooling during the post-collisional stage of the Araçuaí orogen.Item O efeito do microfissuramento no desenvolvimento de patologias em rochas ornamentais : o exemplo dos granitos Branco Viena e Branco Itaúnas.(2019) Calegari, Salomão Silva; Soares, Caroline Cibele Vieira; Hartwig, Marcos Eduardo; Medeiros Júnior, Edgar Batista de; Marques, Rodson de Abreu; Pontello, MarianaO objetivo do presente estudo foi o de investigar as causas das patologias (pequenos pontos acastanhados) que surgem nos granitos Branco Viena e Branco Itaúnas durante ou logo após o seu desdobramento em chapas, o que afeta a sua comercialização. Para tanto, estes materiais foram analisados quanto a suas propriedades físicas, químicas e mineralógicas. Os resultados revelaram diferenças marcantes na densidade, abertura e padrão de distribuição de microfissuras entre os dois materiais, bem como na porosidade aparente, absorção d’água e velocidade de propagação de ondas ultrassônicas. Os dados revelaram que as patologias são causadas pelo microfissuramento dos materiais, sendo este efeito mais pronunciado no granito Branco Itaúnas. Os pontos acastanhados (óxido de Fe) são o produto da alteração química (acelerada) de cristais de granada (Almandina)