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Chemale F.,University of Brasilia | Dussin I.A.,University of Sao Paulo | Alkmim F.F.,DEGEO EM UFOP | Martins M.S.,Federal University of Minas Gerais | And 3 more authors.
Gondwana Research | Year: 2012

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 intraplate conditions: (i) the Lower Espinhaço Basin is marked by a volcano-sedimentary sequence with alluvial, fluvial and eolian deposits that were formed from 1.68. Ga to 1.80. Ga; (ii) the overlying sequence, called the Upper Espinhaço Basin, is a rift-sag basin that presents basal diamond-bearing continental deposits (the Sopa-Brumadinho Formation) with a younger zircon peak at 1192. Ma, which is the maximum age for deposition of the upper units. The obtained U-Pb detrital zircon data of the studied units show age groupings related to the orogenic cycles of Jequié (Neoarchean) and Transamazonian (Paleoproterozoic), which are associated with the stability period from 1.8. Ga to 0.91. Ga in the São Franscico Craton, and record deposition during at least the three basinal cycles. The Stenian-Tonian ages of the Upper Espinhaço Basin units (906. Ma to 1192. Ma) suggest a direct link with the evolution of the Rodinia Supercontinent and represent a marker for Mesoproterozoic to Early Neoproterozoic evolution in the São Franscico Craton and adjacent areas. © 2011 International Association for Gondwana Research.

Santos M.N.,University of Brasilia | Santos M.N.,Petrobras | Chemale F.,University of Brasilia | Dussin I.A.,State University of Rio de Janeiro | And 5 more authors.
Sedimentary Geology | Year: 2015

The Mesoproterozoic Conselheiro Mata Group is the uppermost sequence of the Proterozoic intracontinental Espinhaço basin that developed on the Congo-São Francisco Paleoplate. This sequence is represented by a marine shallow-water platform that experienced a sag phase followed by a rift phase in the Upper Espinhaço. We used combined sedimentological-stratigraphic descriptions of sections, whole-rock (WR) geochemistry and U-Pb detrital zircon dating to develop a regional paleogeographic evolution model of the sag phase. The succession corresponds to transgressive-regressive cycles in the following ascending order: 1) offshore to lower shoreface facies represented by quiescent periods and episodic sediment supply (Santa Rita Formation); 2) upper shoreface to foreshore and coastal desert facies with a reworking of the underlying units (Córrego dos Borges Formation); 3) lower shoreface with fallout of suspended fine sediments and a combination of unidirectional and oscillatory flows generated by storm waves (Córrego da Bandeira Formation); 4) tidal-influenced upper shoreface to foreshore facies with the migration of subaqueous dunes, wave swash in a beach environment and cycles of neap-spring tides (Córrego Pereira Formation); and 5) the resumption of lower-shoreface sedimentation and the subsequent development of a stromatolitic carbonate-siliciclastic platform (Rio Pardo Grande Formation). The geochemical data indicate that the studied units contain input from felsic rocks and sedimentary rocks. The basal marine to eolian sediments of the Galho do Miguel Formation are dominated by Rhyacian sources (2.1. Ga). The basal and intermediate units of the Conselheiro Group contain Archean, Rhyacian, Statherian and Calymmian-Ectasian (1.6-1.33. Ga) zircon grains, whereas Orosirian (1.9-2.0. Ga) sources dominate in the upper strata of the group. The study of this Stenian (Mesoproterozoic) intracratonic sequence provides clues to understanding the history of sedimentation and the potential source areas on the São Francisco Craton and adjacent areas, which are very useful for comparison to Phanerozoic intracratonic basins and the reconstruction of Paleoproterozoic and Mesoproterozoic supercontinents. © 2014 Elsevier B.V.

Goncalves C.C.,DEGEO EM UFOP | Hirth G.,Brown University | Lagoeiro L.,DEGEO EM UFOP
Revista Escola de Minas | Year: 2012

Samples of Banded Iron Formation (BIF) with different quartz and hematite contents were deformed in axial compression experiments in a Griggs-type apparatus, at T = 900oC, P =1.5 GPa and strain rates of 10-5 and 10-6 s-1. The aim is to investigate the mineral phase that controls the rheology of multi-phase rocks and to determine the processes that control the observed rock strength. BIF samples from Quadrilátero Ferrífero region-Brazil were cored perpendicular to the foliation, which is defined by parallel bands of quartz and iron oxide. Sample strength decreases with increasing hematite content and decreasing strain rate. At a strain rate of 10-5 s-1, samples with well-developed compositional banding showed higher strength. At the slower strain rate of 10-6 s-1 no difference between samples with or without compositional banding is observed. For comparison, at 10-6 s-1, the highest quartz content sample is as weak as the highest hematite content sample at 10-5 s-1. Strain is localized in hematite-rich layers. One intriguing observation is that quartz grains within the more deformed hematite-rich bands show more evidence for crystal-plastic deformation than grains in quartz-rich bands.

Sanchez M.G.P.,DEGEO EM UFOP | Gomes N.S.,DEGEO EM UFOP | Carneiro M.A.,DEGEO EM UFOP | Goncalves M.A.,DEQUI ICEB UFOP | Delicio M.P.,DEGEO EM UFOP
Revista Escola de Minas | Year: 2010

This work describes the main mineralogical, physical and geochemical characteristics of the diatom lutites of the Villingota Member of the Tosagua Formation, located in the Progreso Basin in the Southwest of the Equatorian coast, with the view of using them as raw materials in the ceramic industry by means of alkaline activation. The studied pelites of the Villingota Member are composed of a complex mixture characterized by their chemical composition with predominance of silica, carbonate, and alumina, as well as by their varied microfossil fauna that includes diatoms, radiolarians, spicules and foraminifers. The alkaline activation of this natural mixture turned possible the manufacture of geopolymers, which are inorganic materials that can substitute binders and mineral products.

This article presents the results of a petrogenetic and geochemical study carried out for granitoid plutons of the G1 Suite of the Araçuaí orogen, exposed in the region between Governador Valadares and Ipanema (MG). The G1 Suite comprises three distinct lithofacies, namely enderbitic-tonalitic, granodioritic-tonalitic and granitic, which show chemical characteristics similar to an expanded calc-alkaline, metaluminous to slightly peraluminous I-type assemblage. Investigation results indicate that each individual G1 lithofacies represents an evolutionary stage of granitic magmatism, the enderbitic-tonalitic and granitic corresponding to the least and most differentiated components, respectively. Together with the volcanic rocks of the Rio Doce Group, the studied G1 rocks made up the magmatic arc of the Araçuaí orogen, developed on a continental margin between 630 and 585 Ma.

Meunier J.D.,Aix - Marseille University | Varajao A.F.D.C.,DEGEO EM UFOP | Varajao C.A.C.,DEGEO EM UFOP | Colin F.,Aix - Marseille University | Grauby O.,Aix - Marseille University
Journal of South American Earth Sciences | Year: 2013

Due to the poor preservation of old peat formations and the limited research developed on them, the contribution of peat oxidation to the global C cycle at geological scales is poorly understood. Iron duricrusts containing abundant well-preserved plant structures have been reported above Humic Gleysols in the Uberaba Plateau (Brazil). We show that the iron accumulation results from an in-situ impregnation of peat, fast enough to preserve the plant structures. The formation of iron oxides results from two processes: precipitation in the pores and C/Fe replacement. The iron duricrusts were probably triggered by oxidation of the peatland following dry climatic events during the last 50 kyr. The large amount of iron dissolved in peatland waters was immobilized contemporaneously with the destruction of organic matter. The oxidation of organic matter from the lower peat, dated at ca 24-27 kyr BP, may have released between 0.08 and 2.26 kg CO2 m-2 yr-1 in the atmosphere. These rates are in a good agreement with present-day measurements of CO2 release from drained peatlands. Although peatland formation has been identified as a significant contributor to the global CO2 uptake, our findings suggest that natural peatland oxidation should also be considered as a source of atmospheric CO2 during past climate change. © 2012 Elsevier Ltd.

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