U–Pb ages and Hf-isotope data of detrital zircons from the late Neoarchean-Paleoproterozoic Minas Basin, SE Brazil

Because of its world-class iron ore deposits and promising Au and U mineralizations, the late Neoarchean to Paleoproterozoic Minas Basin (Minas Supergroup, SE of Brazil) is one of the best-studied basins in South America. However, the lack of datable interlayered volcanic rocks prevented discourse over ages of the strata, the sources and the nature of its ore deposits. In this paper, we present detrital zircon U–Pb age patterns coupled with Lu–Hf data for 18 samples, representing different stages of the Minas Basin evolution (∼2000 analyzed zircons). Age spectra for the main basal unit (Moeda Formation) show a classic rift-related detrital zircon pattern, characterized by multiple autochthonous sources, which in turn are much older than the age of deposition. Maximum age for the rifting event is constrained at ca. 2600 Ma. Detritus accumulated at the base of the Minas Supergroup were derived from Archean source rocks and their sedimentation was marked by differential uplift of the Archean crust, shortly after the 2730–2600 Ma high-K calc-alkaline magmatism (Mamona Event). The age of the BIF deposits is younger than 2600 Ma, most likely coinciding with the great oxygenation event between 2400 and 2200 Ma and the precipitation of banded iron deposits worldwide. Detrital zircons from the topmost units of the Minas strata suggest that tectonic inversion and closure of the basin took place at ca. 2120 Ma with the deposition of the synorogenic Sabará Group. Rhyacian zircon supply showing juvenile Hf signatures gives evidence of a late Rhyacian amalgamation between the Mineiro Belt and the craton. The εHf signatures support the hypothesis that the Archean crystalline crust of the craton was mostly built by crust–mantle mixing processes, with a successive decrease of εHf values in zircons crystallized after 3250 Ma and minor mantle-like additions after Paleoarchean times. Regionally, our dataset supports previous interpretations of a long-lived evolution of the southern São Francisco Craton comprising a succession of convergent island arcs, small microplate collisions, and development of Archean convergent and divergent basins that evolved between Archean and Paleoproterozoic times.Fil: Martínez Dopico, Carmen Irene. Universidade Federal de Ouro Preto; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lana, Cristiano. Universidade Federal de Ouro Preto; BrasilFil: Moreira, Hugo S.. University of Portsmouth; Reino UnidoFil: Cassino, Lucas F.. Universidade Federal de Ouro Preto; BrasilFil: Alkmim, Fernando F.. Universidade Federal de Ouro Preto; Brasi

U?Pb ages and Hf-isotope data of detrital zircons from the late Neoarchean-Paleoproterozoic Minas Basin, SE Brazil.

Because of its world-class iron ore deposits and promising Au and U mineralizations, the late Neoarchean to Paleoproterozoic Minas Basin (Minas Supergroup, SE of Brazil) is one of the best-studied basins in South America. However, the lack of datable interlayered volcanic rocks prevented discourse over ages of the strata, the sources and the nature of its ore deposits. In this paper, we present detrital zircon U? Pb age patterns coupled with Lu?Hf data for 18 samples, representing different stages of the Minas Basin evolution ( 2000 analyzed zircons). Age spectra for the main basal unit (Moeda Formation) show a classic rift-related detrital zircon pattern, characterized by multiple autochthonous sources, which in turn are much older than the age of deposition. Maximum age for the rifting event is constrained at ca. 2600 Ma. Detritus accumulated at the base of the Minas Supergroup were derived from Archean source rocks and their sedimentation was marked by differential uplift of the Archean crust, shortly after the 2730?2600 Ma high-K calc-alkaline magmatism (Mamona Event). The age of the BIF deposits is younger than 2600 Ma, most likely coinciding with the great oxygenation event between 2400 and 2200 Ma and the precipitation of banded iron deposits worldwide. Detrital zircons from the topmost units of the Minas strata suggest that tectonic inversion and closure of the basin took place at ca. 2120 Ma with the deposition of the synorogenic Sabar? Group. Rhyacian zircon supply showing juvenile Hf signatures gives evidence of a late Rhyacian amalgamation between the Mineiro Belt and the craton. The eHf signatures support the hypothesis that the Archean crystalline crust of the craton was mostly built by crust?mantle mixing processes, with a successive decrease of eHf values in zircons crystallized after 3250 Ma and minor mantle-like additions after Paleoarchean times. Regionally, our dataset supports previous interpretations of a long-lived evolution of the southern S?o Francisco Craton comprising a succession of convergent island arcs, small microplate collisions, and developmen

Ensino de Geociências na universidade

In colonial times, in Brazil, although intense mining activities occurred in the search for gold and diamonds, relevant geoscientific actions did not occur. In the 19th century, a few geological exploratory trips were made, from which several written contributions resulted. Moreover, important institutions were created, such as the National Observatory, the Meteorological Service, the Magnetic Observatory at Vassouras and the Mining School of Ouro Preto in 1876, The formal teaching of Geosciences in Brazil started only in 1957, with the ”Campaign for the training of geologists” (CAGE), that created and provided material and human resources to four Geology undergraduate courses. In Meteorology the first course was in 1973, in Oceanography in 1971 and in Geophysics in 1983. Now, 48 Brazilian universities offer 71 undergraduate courses in Geosciences, 33 in Geology, 3 in Geological Engineering, 14 in Meteorology, 13 in Oceanography and 8 in Geophysics. Fifty-seven graduate programs exist in Brazil, 13 of which are considered of excellence, indicating that the area is mature and consolidated. Most geologists and geophysicists were absorbed in geological mapping activities, as well as mining and oil exploration. Meteorologists dedicated themselves to meteorological and climatic monitoring, as well as to projects in hydroelectric, wind and solar energy. Graduates in Oceanography worked in institutions related to the environment, agriculture, and to the Ministry of the Navy. The atmospheric and oceanographic sciences are of global relevance in studies of climatic changes and global warming. In turn, the major challenge of geologists and geophysicists is to improve knowledge of the Brazilian territory, at the local and regional scale.No Brasil colonial, apesar de intensa atividade mineira na busca de ouro e diamantes, não houve práticas geocientíficas relevantes. No século XIX ocorreram diversas explorações geológicas, das quais resultou uma vasta contribuição escrita. Além disso foram criadas importantes instituições, como o Observatório Nacional, o Serviço Meteorológico, o Observatório Magnético de Vassouras e a Escola de Minas de Ouro Preto em 1876. O ensino formal de Geociências no Brasil foi iniciado apenas em 1957, com a Campanha de Formação de Geólogos (CAGE), que criou e forneceu recursos materiais e humanos para quatro cursos de graduação em Geologia. Na Meteorologia a graduação se iniciou em 1963, na Oceanografia em 1971, e na Geofísica em 1983. Atualmente, 47 universidades brasileiras oferecem 71 cursos de graduação nas Geociências. Há 33 cursos de Geologia, três de Engenharia Geológica, 14 de Meteorologia, 13 de Oceanografia e 8 de Geofísica. Há no Brasil 57 programas de pós-graduação em Geociências, 13 dos quais considerados de excelência, indicando que a situação atual da área é de consolidação e maturidade. Geólogos e geofísicos foram absorvidos, em sua maioria, pelas atividades de mapeamento geológico, exploração mineral e de petróleo. Meteorologistas dedicaram-se ao monitoramento meteorológico e climático, e também a projetos de energia hidroelétrica, eólica e solar. Na Oceanografia, os formados atuaram em órgãos relacionados com ambiente, agricultura e no Ministério da Marinha. Quanto à pesquisa, as ciências atmosféricas e oceanográficas são de grande relevância global, no estudo das mudanças climáticas e o aquecimento global. Por sua vez, o maior desafio de geólogos e geofísicos é o de melhorar do conhecimento do território brasileiro, na escala local ou regional

Palaeoproterozoic Assembly of the São Francisco craton crust, SE Brazil: New insights from U-Pb titanite and monazite dating

Isotopic U-Pb titanite and monazite data from the southern São Francisco craton better constrain the timing of the tectono-thermal event that led to the amalgamation of the craton and the crust that forms the basement of its fringing orogenic belts in the Palaeoproteroic. The data obtained from assemblages exposed in the Quadrilátero Ferrífero mining district and adjacent Palaeoproterozoic Mineiro belt magmatic arc terrane reveal two different age populations: a first metamorphic event between 2772 and 2613 Ma, followed by recrystallization or/and isotopic resetting in the interval of 2080-1940 Ma. The partial preservation of Neoarchaean ages in the craton interior suggests that the Palaeoproterozoic metamorphism did not exceed the minimum closure temperature for the titanite (between 650 C and 700 C), which is also reinforced by the absence of Palaeoproterozoic metamorphic zircons in the southern São Francisco craton. Combining new and existing Palaeoproterozoic data, we infer that the Archaean crust of the southern craton as well as the surrounding magmatic arcs were affected by a long-lived metamorphic event from ca. 2100 Ma to 1940 Ma. These age interval includes an episode of syn-collisional metamorphism between 2100 and 2070 Ma, which represents the amalgamation of the Archaean nuclei of both the São Francisco and Congo cratons, along with magmatic arcs and microcontinents. This collision led to closure of the large Palaeoproterozoic Minas basin, followed by orogenic collapse and development of a dome-and-keel architecture in time interval of 2070-2050 Ma. A period of slow cooling ( 1 C/Ma) succeeded these events and lasted until ca. 1940 Ma. Our results correlate with the Palaeoproterozoic metamorphic ages obtained in the various blocks forming the northeastern sector of the craton

Stabilization of the southern portion of the São Francisco craton, SE Brazil, through a long-lived period of potassic magmatism

Although the southern portion of the São Francisco craton in southeast Brazil encompasses one of the largest segments of Meso- to Neoarchaean crust in the South American plate, there is little understanding of the processes leading to cratonization of t

The Archean - Paleoprotorozoic evolution of Quadrilátero Ferrífero (Brazil): current models and open questions

The Quadril atero Ferrífero is a metallogenic district (Au, Fe, Mn) located at the southernmost end of the S~ao Francisco craton in eastern Brazil. In this region, a supracrustal assemblage composed of Archean greenstone and overlying NeoarcheanePaleoproterozoic sedimentary rocks occur in elongated keels bordering domal bodies of Archean gneisses and granites. The tectonomagmatic evolution of the Quadrila tero Ferrífero began in the Paleoarchean with the formation of continental crust between 3500 and 3200 Ma. Although this crust is today poorly preserved, its existence is attested to by the occurrence of detrital zircon crystals with Paleoarchean age in the supracrustal rocks. Most of the crystalline basement, which is composed of banded gneisses intruded by leucogranitic dikes and weakly foliated granites, formed during three major magmatic events: Rio das Velhas I (2920e2850 Ma), Rio das Velhas II (2800e2760 Ma) and Mamona (2760e2680 Ma). The Rio das Velhas II and Mamona events represent a subduction-collision cycle, probably marking the appearance of a modern-style plate tectonic regime in the Quadrila tero Ferrífero. Granitic rocks emplaced during the Rio das Velhas I and II events formed by mixing between a magma generated by partial melting of metamafic rocks with an end member derived by recycling gneissic rocks of older continental crust. After deformation and regional metamorphism at ca. 2770 Ma, a change in the composition of the granitic magmas occurred and large volumes of high-K granitoids were generated. The ca. 6000 m-thick Minas Supergroup tracks the opening and closure of a basin during the Neo- archeanePaleoproterozoic, between 2600 and 2000 Ma. The basal sequence involves continental to marine sediments deposited in a passive margin basin and contain as a marker bed the Lake Superior- type Caue^ Banded Iron Formation. The overlying sediments of the Sabara Group mark the inversion of the basin during the Rhyacian Minas accretionary orogeny. This orogeny results from the collision be- tween the nuclei of the present-day S~ao Francisco and Congo cratons, generated the fold-and thrust belt structure of the Quadril atero Ferrífero. Afterwards, the post- orogenic collapse resulted in the deposition of the Itacolomi Group and in the genesis of the dome-and-keel structure. In this paper, we review current knowledge about the 1500 Ma long-lasting tectonomagmatic and structural evolution of the Quadril atero Ferrífero identifying the most compelling open questions and future challenges

The ancestry and magmatic evolution of Archaean TTG rocks of the Quadrilatero Ferra-fero province, southeast Brazil

Combined LA-ICP-MS and SHRIMP U-Pb ages from Quadrilátero Ferrífero (QF) province reveals for the first time three main periods of TTG magmatism in the southern part of the São Francisco Craton (Brazil). These periods - described here as the Santa Bar

Unravelling a Proterozoic basin history through detrital zircon geochronology: The case of the Espinhaco Supergroup, Minas Gerais, Brazil

New U-Pb in situ zircon dating provides a new approach for the study of the Espinhaço Supergroup units exposed in the São Francisco Craton and Araçuaí Orogen. Located in Southern Espinhaço, Minas Gerais, the following two basins were formed in intra

Ensino de Geociências na universidade

RESUMO No Brasil colonial, apesar de intensa atividade mineira na busca de ouro e diamantes, não houve práticas geocientíficas relevantes. No século XIX ocorreram diversas explorações geológicas, das quais resultou uma vasta contribuição escrita. Além disso foram criadas importantes instituições, como o Observatório Nacional, o Serviço Meteorológico, o Observatório Magnético de Vassouras e a Escola de Minas de Ouro Preto em 1876. O ensino formal de Geociências no Brasil foi iniciado apenas em 1957, com a Campanha de Formação de Geólogos (CAGE), que criou e forneceu recursos materiais e humanos para quatro cursos de graduação em Geologia. Na Meteorologia a graduação se iniciou em 1963, na Oceanografia em 1971, e na Geofísica em 1983. Atualmente, 47 universidades brasileiras oferecem 71 cursos de graduação nas Geociências. Há 33 cursos de Geologia, três de Engenharia Geológica, 14 de Meteorologia, 13 de Oceanografia e 8 de Geofísica. Há no Brasil 57 programas de pós-graduação em Geociências, 13 dos quais considerados de excelência, indicando que a situação atual da área é de consolidação e maturidade. Geólogos e geofísicos foram absorvidos, em sua maioria, pelas atividades de mapeamento geológico, exploração mineral e de petróleo. Meteorologistas dedicaram-se ao monitoramento meteorológico e climático, e também a projetos de energia hidroelétrica, eólica e solar. Na Oceanografia, os formados atuaram em órgãos relacionados com ambiente, agricultura e no Ministério da Marinha. Quanto à pesquisa, as ciências atmosféricas e oceanográficas são de grande relevância global, no estudo das mudanças climáticas e o aquecimento global. Por sua vez, o maior desafio de geólogos e geofísicos é o de melhorar do conhecimento do território brasileiro, na escala local ou regional