Uranium-lead dating method at the Pará-Iso isotope geology laboratory, UFPA, Belém - Brazil

Analytical procedures for U-Pb isotope dilution analyses at the Pará-Iso isotope geology laboratory of the Federal University of Pará (UFPA) are described in detail. The procedures are applied to zircon, titanite, rutile, apatite, columbite-tantalite and whole rock. Reagent preparation and chemical processing are done in clean-room conditions. Samples are dissolved using TeflonTM microcapsules in steel jacket TeflonTM Parr InstrumentTM bomb or TeflonTM screw cap containers. U and Pb are separated using anion exchange AG 1x8 resin columns. Typical blanks for mineral sample amounts of 0.01 to 1.0 mg are less than 1 pg U and 20-30 pg Pb. Isotope analysis of the U and Pb from the same filament are carried out using a Finnigan MAT 262 mass-spectrometer in static and dynamic modes. The current analytical level is demonstrated on analyses of international standard zircon 91500 with three different 235U-205Pb and 235U-208Pb isotope tracers and whole rock standards. Results of analyses of two zircon samples are also presented

Brazilian Analog For Ancient Marine Environments On Mars

[No abstract available]8936329330Bibring, J., Mars surface diversity as revealed by the OMEGA/Mars Express observations (2005) Science, 307, pp. 1576-1581Christensen, P.R., Detection of crystalline hematite mineralization on Mars by the Thermal Emission Spectrometer. Evidence for near-surface water (2000) J. Geophys. Res, 105, pp. 9623-9642Connerney, J.E.P., Magnetic lineations in the ancient crust of Mars (1999) Science, 284, pp. 794-798Crowley, J.K., Spectral diversity of terrestrial banded iron formations and associated rocks: Implications for Mars remote sensing (2008) Lunar Planet Sci, 39, p. 1263Dalstra, H., Guedes, S., Giant hydrothermal hematite deposits with Mg-Fe metasomatism: A comparison of the Carajas, Hamersley, and other iron ores (2004) Econ. Geol, 99, pp. 1793-1800Fallacaro, A., Calvin, W.M., Spectral properties of Lake Superior banded iron formation: Application to Martian hematite deposits (2006) Astrobiology, 6, pp. 563-580Klein, C., Some Precambrian banded-iron formations (BIFs) from around the world: Their age, geologic setting, mineralogy, metamorphism, geochemistry, and origin (2005) Am. Mineral, 90, pp. 1473-1499Klein, C., Ladeira, E.A., Petrography and geochemistry of the least altered banded iron-formation of the Archean Carajas Formation, northern Brazil (2002) Econ. Geol, 97, pp. 643-651Squyres, S.W., In situ evidence for an ancient aqueous environment at Meridiani Planum, Mars (2004) Science, 306, pp. 1709-1714Trendall, A.F., The significance of iron-formation in the Precambrian stratigraphic record (2002) Spec. Publ. Int. Assoc. Sedimentol, 33, pp. 33-66Trendall, A.F., Basei, M.A.S., de Laeter, J.R., Nelson, D.R., Ion microprobe zircon, U-Pb results from the Carajas area of the Amazon craton (1998) J. S. Am. Earth Sci, 11, pp. 265-27

Durabilidade de madeira de eucalipto citriodora (Corymbia citriodora (Hook.) K.D. Hill & L.A.S. Johnson) tratada com CCA em ambiente amazônico Durability of eucalyptus citriodora wood (Corymbia citriodora (Hook.) K.D. Hill & L.A.S. Johnson) treated with CCA in the Amazon environment

A intensa exploração econômica tem causado diminuição do estoque original das espécies madeireiras amazônicas, incluindo aquelas de alta durabilidade natural destinadas a usos em contato com o solo. A escassez dessas madeiras resulta na elevação do preço, inviabilizando economicamente seu uso, sendo uma alternativa a substituição por espécies plantadas de rápido crescimento tratadas com preservativos. Outra vantagem, além da econômica, de utilizar espécies plantadas em substituição às tradicionais é ambiental, pois reduzirá a pressão exploratória sobre aquelas. Este estudo teve por objetivo avaliar o grau de degradação biológica de madeira de eucalipto citriodora (Corymbia citriodora (Hook.) K.D. Hill & L.A.S. Johnson) tratado por processo a vácuo e pressão com arseniato de cobre cromatado (CCA) e exposta em ensaio de campo em Rio Branco-AC. O ensaio foi implantado em maio de 2005 com estacas tratadas ou não com CCA. As variáveis avaliadas foram: 1) degradação por fungos, 2) degradação por cupins, e 3) região ou parte da peça afetada. A partir da terceira avaliação (47 meses de ensaio), 100% dos corpos de prova não tratados foram classificados com o grau de degradação máximo e, ao contrário, 100% dos tratados com CCA, decorridos 60 meses de ensaio, foram classificados com o grau mínimo. As partes não tratadas com maior e menor grau de degradação foram, respectivamente, o topo inferior e a parte aérea acima de 10 cm do solo. A degradação provocada por fungos foi levemente inferior à dos cupins. O ensaio aponta para a viabilidade técnica do uso de madeira tratada de eucalipto em substituição às espécies tradicionais da Amazônia.<br>The intense economic exploration has caused a decrease of the original stock of Amazon woody species, including those of high natural durability used in soil contact. The lack of those species results in increased price that makes economically unfeasible of the use, an alternative is the replacement by planted species of fast-growing treated with preservatives. Another advantage of to use species planted to replace the traditional species is environmental, because this will reduce the exploratory pressure on these species. The objective of this study is to evaluate the degree of biological degradation of eucalyptus citriodora wood (Corymbia citriodora (Hook.) K.D. Hill & L.A.S. Johnson) treated with chromated copper arsenate (CCA) under vacuum and pressure process and exposed in field experiment in Rio Branco-AC. The experiment was implemented in May 2005 with cuttings treated with CCA and not treated. The variables evaluated were: 1) degradation by fungi, 2) degradation by termites, and 3) region or part of the piece affected. After the 3rd evaluation (47 months of test), 100% of the specimens without treated were classified with the maximum degree of degradation and, in contrast, 100% of the specimens treated with CCA, after 60 months of test, were classified with the minimum degree of degradation. The parties of the pieces without treatment with the higher and the lesser degrees of degradation were, respectively, the inferior head and the aerial part above 10 cm of soil. The degradation caused by fungi was slightly lower than that of termites. The field experiment has shown that is technically feasible the use of eucalyptus wood to replace the traditional species of the Amazon