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Almeida J.D.A.C.D.,Federal University of Para | Dall'Agnol R.,Federal University of Para | Dall'Agnol R.,Instituto Tecnologico Vale Desenvolvimento Sustentavel | Leite A.A.D.S.,Terrativa Minerais S.A
Journal of South American Earth Sciences | Year: 2013

The Archean granites exposed in the Mesorchean Rio Maria granite-greenstone terrane (RMGGT), southeastern Amazonian craton can be divided into three groups on the basis of petrographic and geochemical data. (1) Potassic leucogranites (Xinguara and Mata Surrão granites), composed dominantly of biotite monzogranites that have high SiO2, K2O, and Rb contents and show fractionated REE patterns with moderate to pronounced negative Eu anomalies. These granites share many features with the low-Ca granite group of the Yilgarn craton and CA2-type of Archean calc-alkaline granites. These granites result from the partial melting of rocks similar to the older TTG of the RMGGT. (2) Leucogranodiorite-granite group (Guarantã suite, Grotão granodiorite, and similar rocks), which is composed of Ba- and Sr-rich rocks which display fractionated REE patterns without significant Eu anomalies and show geochemical affinity with the high-Ca granite group or Transitional TTG of the Yilgarn craton and the CA1-type of Archean calc-alkaline granites. These rocks appear to have been originated from mixing between a Ba- and Sr-enriched granite magma and trondhjemitic liquids or alternatively product of interaction between fluids enriched in K, Sr, and Ba, derived from a metasomatized mantle with older TTG rocks. (3) Amphibole-biotite monzogranites (Rancho de Deus granite) associated with sanukitoid suites. These granites were probably generated by fractional crystallization and differentiation of sanukitoid magmas enriched in Ba and Sr.The emplacement of the granites of the RMGGT occurred during the Mesoarchean (2.87-2.86 Ga). They are approximately coeval with the sanukitoid suites (∼2.87 Ga) and post-dated the main timing of TTG suites formation (2.98-2.92 Ga). The crust of Rio Maria was probably still quite warm at the time when the granite magmas were produced. In these conditions, the underplating in the lower crust of large volumes of sanukitoid magmas may have also contributed with heat inducing the partial melting of crustal protoliths and opening the possibility of complex interactions between different kinds of magmas. © 2012 Elsevier Ltd. Source


da Silva A.K.T.,Federal University of Para | Guimaraes J.T.F.,Instituto Tecnologico Vale Desenvolvimento Sustentavel | Lemos V.P.,Federal University of Para | da Costa M.L.,Federal University of Para | Kern D.C.,Museu Paraense Emilio Goeldi
Acta Amazonica | Year: 2012

The comparison of morphological, mineralogical and chemical data of a soil with anthropic horizons - Archeological Black Earth (ABE) and surrounding Argissolos (Typic Kandiudox or Ultisols) allowed the identification of the main process acting on the ABE formation from the town of Bom Jesus do Tocantins, southeastern Pará State. The similarity between the data in the subsurface horizons of ABE and surrounding soils indicates that the former was likely developed from Argissolos with later pedogenetic transformation by the input of organic and inorganic materials from ancient human settlements, which resulted in thickness of the surface horizon and higher concentrations of CaO and P2O5 (total content), Zn (trace content), available P and Zn (available content), and exchangeable Ca and Mg (exchangeable content) compared to surrounding Argissolos. Furthermore, such anthropic disturbance also resulted in changes in the subsurface horizon of Argissolos with ABE, such as high concentrations of P2O5 and available P. The Soil Taxonomy and Brazilian System of Soil Classification (BSSC) are suitable to identify soils with ABE, as they prioritize at the highest categorical level the main pedogenetic process acting on soil development and formation, related to the subsurface horizons, and later pedogenetic transformations in the surface horizon. However, this study proposes the addition of diagnostic properties such as ceramic and lithic artifacts, P2O5 and available P and Zn, organic C, Ca2++ Mg2+ (exchangeable content), CEC and base saturation in the surface horizon to classify and discriminate several kinds of anthropic soils in the Amazon region. Source


Mendoza M.R.,Federal University of Rio Grande do Sul | da Fonseca G.C.,Federal University of Rio Grande do Sul | Loss-Morais G.,Federal University of Rio Grande do Sul | Alves R.,Instituto Tecnologico Vale Desenvolvimento Sustentavel | And 2 more authors.
PLoS ONE | Year: 2013

MicroRNAs are key regulators of eukaryotic gene expression whose fundamental role has already been identified in many cell pathways. The correct identification of miRNAs targets is still a major challenge in bioinformatics and has motivated the development of several computational methods to overcome inherent limitations of experimental analysis. Indeed, the best results reported so far in terms of specificity and sensitivity are associated to machine learning-based methods for microRNA-target prediction. Following this trend, in the current paper we discuss and explore a microRNA-target prediction method based on a random forest classifier, namely RFMirTarget. Despite its well-known robustness regarding general classifying tasks, to the best of our knowledge, random forest have not been deeply explored for the specific context of predicting microRNAs targets. Our framework first analyzes alignments between candidate microRNA-target pairs and extracts a set of structural, thermodynamics, alignment, seed and position-based features, upon which classification is performed. Experiments have shown that RFMirTarget outperforms several well-known classifiers with statistical significance, and that its performance is not impaired by the class imbalance problem or features correlation. Moreover, comparing it against other algorithms for microRNA target prediction using independent test data sets from TarBase and starBase, we observe a very promising performance, with higher sensitivity in relation to other methods. Finally, tests performed with RFMirTarget show the benefits of feature selection even for a classifier with embedded feature importance analysis, and the consistency between relevant features identified and important biological properties for effective microRNA-target gene alignment. © 2013 Mendoza et al. Source


da Costa M.A.C.,Geological Survey of Brazil SGB CPRM | de Sousa M.Z.A.,Federal University of Mato Grosso | Dall'Agnol R.,Federal University of Para | Dall'Agnol R.,Instituto Tecnologico Vale Desenvolvimento Sustentavel | And 2 more authors.
Journal of South American Earth Sciences | Year: 2016

The Serra da Providência batholith includes the type area of the homonymous suite, the oldest rapakivi magmatic assemblage in the SW of the Amazonian craton (1.60-1.53 Ga). In the midwest portion of this massif, besides wiborgites/pyterlites and granophyric syenogranites, a leucosyenogranite facies and porphyritic rhyolites constitute new rock varieties recently described in that area. UPb LA-MC-ICP-MS zircon ages of 1574 ± 9 Ma and 1604 ± 3 Ma, respectively, were obtained for these new varieties and confirm their link with the Serra da Providência magmatism, whereas the subvolcanic rocks are older than the main rock varieties and were formed in a precursor event. These granitic facies are metaluminous to peraluminous, alkali-calcic, A2-type, ferroan granites. Their FeOt/(FeOt + MgO) ratios vary from 0.83 to 0.98 and suggest that these rocks were crystallized from oxidized-to reduced-A-type magmas, where the leucosyenogranites and granophyric sienogranites tend to be formed under more reduced conditions. They show fractionated REE patterns with very pronounced to weak negative Eu anomalies. The presence of granophyric textures and miarolitic cavities in equigranular syenogranitic facies suggests that these rocks were formed at shallow crustal depths, lower than 3 km. Three samples of leucosyenogranite have silica contents higher than 75% and low K/Rb ratios (<150), similarly to the tin specialized granites described in the Amazonian craton. Two distinctive groups of mafic rocks were recognized in the study area: porphyritic and equigranular gabbronorites. They correspond to tholeiitic basalts, with #Mg varying from 37 to 41 in porphyritic gabbronorites and 51 to 65 in equigranular gabbronorites. The low to moderate #Mg suggests that these rocks were crystallized from more evolved basaltic magmas. The porphyritic gabbronorites are enriched in TiO2, FeOt, K2O, P2O5 and REE compared to the equigranular gabbronorites that are enriched in MgO and CaO. The porphyritic gabbronorites have significant negative Eu anomalies a feature not observed in the equigranular gabbronorites. Porphyritic gabbronorites geochemical characteristics are similar to calc-alkaline basalts, whereas equigranular gabbronorites are similar to continental basalts. Petrographic, geochemical, and geological data of the felsic facies and the presence of associated mafic rocks corroborate the bimodal and post-collisional character of this magmatism. The occurrence of porphyritic rhyolites associated with shallow level plutonic granites in the Serra da Providência batholith reinforces the similarities between the Rondonian granites and the classical Fennoscandian rapakivi granites. © 2016 Elsevier Ltd. Source


Valadares R.B.S.,University of Sao Paulo | Valadares R.B.S.,Instituto Tecnologico Vale Desenvolvimento Sustentavel | Otero J.T.,National University of Colombia | Pereira M.C.,Federal University of Vicosa | Cardoso E.J.B.N.,University of Sao Paulo
Acta Botanica Brasilica | Year: 2015

In Orchidaceae, association with symbiotic fungi is required for seed germination and seedling development, thereby being the main energy source during the first steps of germination. Colombia is one of the countries with the greatest biodiversity of orchids, with an estimated 3,200 species, but few studies on orchid mycorrhiza have been conducted. In our study, we isolated and sequenced the internal transcribed spacer rDNA region of fungi from two co-occurring Colombian epiphytic orchids, I. utricularioides and P. pusilla, both belonging to the subtribe Oncidiinae. All sequences were recognized as belonging to the genus Ceratobasidium, known to be a common orchid mycorrhizal fungus in both tropical and temperate orchids. One sequence was 100% similar to fungi isolated from I. utricularioides in Costa Rica in a previous study. I. utricularioides was confirmed to be a specialist, associating with only one clade of mycorrhizal fungi. However, P. pusilla was shown to be a generalist, associating with three clades. This finding indicates that the variation in mycorrhizal specificity could be an important factor in the co-existence of orchids. The high affinity between the subtribe Oncidiinae and Ceratobasidium was also reinforced. © 2015, Sociedade Botanica do Brasil. All rights reserved. Source

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