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.
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2 resultados
Resultados da Pesquisa
Item Evidence for change in crust formation process during the Paleoarchean in the São Francisco Craton (Gavião Block) : coupled zircon Lu-Hf and U-Pb isotopic analyses and tectonic implications.(2022) Santos, Cláudia dos; Zincone, Stéfano Albino; Queiroga, Gláucia Nascimento; Bersan, Samuel Moreira; Lana, Cristiano de Carvalho; Oliveira, Elson Paiva deThe continental crust growth/evolution processes and the tectonic regime through Eo- and Paleoarchean times are enigmatic due to the scarcity of preserved crust. The Gaviao ̃ Block, S ̃ ao Francisco Craton (Brazil), contains exposed and well-preserved Eo-Paleoarchean crust remnants, providing a rare opportunity to investigate these issues. Here, we describe new U-Pb ages and Hf isotope data of 3.51–3.4 Ga tonalites and diorites from the Gaviao ̃ Block and compare these with previously published Lu-Hf data from Hadean/Eo-Paleoarquean zircons from the Gavi ̃ ao Block and other primitive cratons. The Eo- to Paleoarchean evolution of the Gaviao ̃ Block is registered by ca. 360 Myr of continuous magmatic events from ca. 3.66 Ga to 3.30 Ga. From the available Hf data, we interpret that each of the events younger than 3.6 Ga registers a new juvenile addition that assimilated older crust, whereas the rocks older than 3.6 Ga are exclusively formed through the reworking of a Hadean, and to a less extent early Eoarchean crust. The shift in the crust generation process with the input of juvenile material into the Gavi ̃ ao Block has been documented within the ~ 3.8–3.5 Ga time in other primitive cratonic complexes including the Wyoming, Pilbara, Kaapvaal, Slave, Singhbhum, and Yilgarn. As documented in these other cra- tons, our data suggest that a shift in the Hf isotope record to rocks younger than 3.6 Ga reflects a transition from stagnant-lid to mobile-lid tectonics in the crust formation process of the S ̃ ao Francisco Craton. This change in the geodynamic regime appears to have been global at ca. ~ 3.8–3.5 Ga and facilitated the extraction of juvenile melts, crustal reworking, evolved magmatism, and the production of stabilizing melt-depleted lithospheric mantle.Item Oceanic crust and mantle evidence for the evolution of tonian-cryogenian ophiolites, southern Brasiliano Orogen.(2020) Werle, Mariana; Hartmann, Leo Afraneo; Queiroga, Gláucia Nascimento; Lana, Cristiano de Carvalho; Silva, Juliana Pertille da; Michelin, Cassiana Roberta Lizzoni; Remus, Marcus Vinicius Dorneles; Roberts, Malcolm; Castro, Marco Paulo de; Leandro, Carolina Gonçalves; Savian, Jairo FranciscoUnravelling the complexity of tonian-cryogenian (950–680 Ma) evolution of ophiolites requires the search for rare mineral systems and their quantification with varied techniques. Ophiolites in the Brasiliano Orogen are widely distributed over 2,000 km along the eastern half of South America. We selected two ophiolites from different geotectonic settings of the Sul-Riograndense Shield, southern Brasiliano Orogen, to delimit the evolution of the oceanic phase of the orogen. The southern portion of the Bossoroca ophiolite is inserted in the Sao ˜ Gabriel juvenile terrane and contains rare metasomatic tourmaline in chloritite close to serpentinite and metamorphosed Cr-spinel. The southern Bossoroca ophiolite was intruded by Cerro da Cria and Ramada Granites and the U-Pb-Hf isotopic study of zircon from these rocks constrains the crustal evolution of the Sao ˜ Gabriel juvenile terrane. Capan´e ophiolite has similar age (793–715 Ma) as the Bossoroca ophiolite and was inserted in the Porongos fold-thrust belt with preserved Cr-spinel of mantellic composition. Integrated use of Cr-spinel mineral chemistry, B isotopes in tourmaline in the Bossoroca ophiolite and zircon U-Pb-Hf isotopes of granites associated with the southern Bossoroca ophiolite revealed several steps in the evolution of the ophiolites in the Dom Feliciano Belt. Capan´e Cr-spinel cores have mantle-derived compositions (Mg# 0.66 – 0.69; Cr# 0.51 – 0.53), tourmaline from the Bossoroca ophiolite is dravite and has δ11B = 0 to + 3, and granites crystallization ages are 578 ± 3.2 and 612 ± 12 Ma (εHfzrn = − 10 to − 25). Zircon from other dravite occurrences of the Bossoroca ophiolite were previously dated at 920 Ma. We unraveled the main steps in the evolution of ophiolites from the southern Brasiliano Orogen, with emphasis on the Bossoroca and Capan´e ophiolites, during their trajectory from mid-ocean ridge (920 Ma), formation of dravite in oceanic crust, preservation of mantellic cores in Cr-spinel, and intrusion of craton-generated granites at 612–578 Ma.