Isotope geochemistry of the mafic dikes from the Vazante nonsulfide zinc deposit, Brazil

The Vazante Group, located in the northwestern part of Minas Gerais, hosts the most important zinc mine in Brazil, the Vazante Mine, which represents a major known example of a hypogene nonsulfide zinc deposit. The main zinc ore is represented by willemite and differs substantially from other deposits of the Vazante-Paracatu region, which are sulfide-dominated zinc-lead ore. The age of the Vazante Group and the hosted mineralization is disputable. Metamorphosed mafic dikes (metabasites) that cut the metasedimentary sequence and are affected by hydrothermal processes recently were found and may shed light on the geochronology of this important geological unit. Zircon crystals recovered from the metabasites are xenocrystic grains that yield U-Pb conventional ages ranging from 2.1 to 2.4 Ga, so the basement of the Vazante Group is Paleoproterozoic or has metasedinientary rocks whose source area was Paleoproterozoic. Pb isotopes determined for titanite separated from the metabasites have common, nonradiogenic Ph compositions, which prevents determination of their crystallization age. However, the Pb signatures observed for the titanite crystals are in agreement with those determined for galena from the carbonate-hosted Zn-Pb deposits hosted by the Vazante Group, including galena from minor sulfide ore bodies of the Vazante deposit. These similarities suggest that the metalliferous fluids that affected the metabasites may have been those responsible for galena formation, which could imply a similar lead source for both nonsulfide and sulfide zinc deposits in the Vazante-Paracatu district. This common source could be related to deep-seated, basin-derived, metalliferous fluids associated with a long-lived hydrothermal system related to diagenesis and deformation of the Vazante Group during the Neoproterozoic. (c) 2005 Elsevier Ltd. All rights reserved.

CROCODYLOMORPH EGGS and EGGSHELLS FROM THE ADAMANTINA FORMATION (BAURU GROUP), UPPER CRETACEOUS of BRAZIL

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Groundwater geochemical evolution in the northern portion of the Guarani Aquifer System (Brazil) and its relationship to diagenetic features

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A new specimen of Stratiotosuchus maxhechti (Baurusuchidae, Crocodyliformes) from the Adamantina Formation (Upper Cretaceous), southeastern Brazil.

This is a report about the second occurrence and description of the third specimen of Stratiotosuchus maxhechti (Baurusuchidae, Crocodyliformes) from the Bauru Basin, Upper Cretaceous of southeastern Brazil. The material was found in the typical reddish, fine-grained sandstone from the Adamantina Formation, Bauru Group, Monte Alto County, São Paulo State. These strata are considered to be Campanian-Maastrichtian in age. It is the second skull of Stratiotosuchus maxhechti recovered where the choanal region and the skull-mandible articulation is preserved. The holotype of this species comes from the Adamantina Formation from southwestern São Paulo State, while this new specimen comes from its northern-central region, making possible biocbronological and paleoccological correlations among different geographically distant stratigraphic horizons within the Bauru Basin. The main osteologic contributions from this new specimen are the surangular taking part in the skull/mandible articulation and the presence of a relatively well-preserved choanal region, which are not seen in the holotype, furthering the knowledge of Stratiotosuchus maxhechti. Based on the features of this new specimen, an emended diagnosis is provided.

Semantic categories in the indigenous languages of Brazil

This article investigates which semantic categories, as defined in Functional Discourse Grammar, formally manifest themselves in a sample of native languages of Brazil, and the extent to which the distribution of these manifestations across categories can be described systematically in terms of implicational hierarchies. The areas subjected to investigation are basic interrogative words, basic demonstrative words, and nominalization strategies.

Astyanax pirapuan: a new characid species from the upper Rio Paraguay system, Mato Grosso, Central Brazil (Characiformes, Characidae)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Physa mezzalirai, a new cretaceous basommatophoran from Adamantina formation, Brazil.

This paper deals with a formal description of Physa mezzalirai (Basommatophora, Physidae), a new species of freshwater gastropod that lived in upper Cretaceous deposits, in sand-silty beds of Adamantina formation, Bauru basin, from Marlia, São Paulo state, Brazil. This formal description legitimates the availability of the name previously described in 2010 by same authors; being this paper the correct citation for the species name.

A new Pennsylvanian Oriocrassatellinae from Brazil and the distribution of the genus Oriocrassatella in space and time

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

The occurrence of Austrodiplostomum compactum (Lutz, 1928) (Digenea: Diplostomidae) metacercariae in the eyes of loricariid fish (Siluriformes: Osteichthyes: Loricariidae) from Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The geotectonic environments of Early Precambrian granulites in Brazil

A review is presented concerning Archaean granulites occurring in some old domains of the South American Platform, which was consolidated at the end of the Brazilian Cycle (900-500 Ma). The rocks occur in different geotectonic environments and show variable ages, structures and lithological associations. The most important complexes are the Atlantic Granulite Belt in the São Francisco Craton and the Goias Granulite Belt in the Central Goias Massif, both several hundred kilometres long. The former is composed of the Caraibas Complex, the Jequié Complex, the Salvador Complex and several minor granulite occurrences along the Brazilian coast in the States of Espírito Santo and Rio de Janeiro. The latter includes the large basic-ultrabasic complexes of Barro Alto, Tocantins and Canabrava. Both belts consist of massive or foliated rocks, banded or homogeneous and varying from acidic to ultrabasic in composition. They are the result of metamorphism affecting diversified supra- and infracrustal material. The Atlantic Granulite Belt lies between greenstone/granite terrains which show ovoid and boomerang-type dome structures. The contacts between both are either tectonic or transitional. Another occurrence of Archaean granulites comprises intercalations of palaeosomes and melanosomes within migmatites and anatectic rocks. These vary in size from small lenses to irregular complexes which may attain sizes of several hundred square kilometres. Apart from migmatites, they are associated with gneisses, schists and granitoid bodies. They are located in regions which underwent remobilization of varying intensity during the Middle and Late Precambrian. The rocks show polymetamorphism, K-feldspar blastesis, tectonic overprinting and isotopic rejuvenation. These granulites are in some cases very similar to those formed during the Middle Precambrian. In some places it is therefore quite difficult to distinguish between Early and Middle Precambrian granulites - the more so, since interpretations of radiometric age values are largely controversial. At present there is no evidence of granulitic rocks related to the Late Precambrian geotectonic cycles of Brazil. © 1979.

Palaeomagnetism of the Mesozoic Serra Geral Formation, southern Brazil

Palaeomagnetic results from 20 volcanic sequences and 11 intrusive bodies (sills and dykes) of the Serra Geral Formation (Paraná Basin) are reported in this paper. The sequences are widespread all over the basin, while sills and dykes (Ponta Grossa arch) come from the northeastern portion. Three mean palaeomagnetic poles were computed for the Serra Geral Formation, which account for a time interval of ∼ 15 Ma. Pole SG1 is located at 85°S,108°E (α95 = 1.1°, N = 18) and represents the main phase of the magmatic activity in the basin, with a mean age of ∼ 135 Ma. Pole SG2 is located at 82°S,38°E (α95 = 7.8°, N = 2) and represents a younger magmatic phase, with an associated age of ∼ 130 Ma. Pole SG3 (72°S,37°E; α95 = 6.8°, N = 10) is the youngest pole. It is computed from the intrusive rocks and its age is assumed to be not younger than 118 Ma, the lower limit of the 'Cretaceous normal magnetic interval'. These three poles describe a shifting path, which suggest that the South American platform moved ∼ 5° southwards and rotated ∼ 10° clockwise during the Lower Cretaceous, preceding the South Atlantic opening. © 1990.

Life strategies of some long-distance migratory catfish in relation to hydroelectric dams in the Amazon Basin

In this paper, we present evidence that the long-distance migratory catfish Brachyplatystoma filamentosum, B. flavicans, B. vaillantii, Goslinia platynema and Lithodoras dorsalis spawn in the headstreams of the Amazon river and its tributaries and that the estuary of the Amazon is the main nursery ground utilized by their alevins. The impact of hydroelectric dams on their populations are discussed in terms of interruption to fish migration routes up river and to larvae moving down river, provided that the hypothesis above holds. Ways of mitigating the impact are also considered. © 1991.

Modelos geotectonicos aplicados ao Pre-Cambriano superior do NE do Estado de Sao Paulo e areas adjacentes do Estado de Minas Gerais: uma discussao

The main geotectonics models presented during the last 25 yr to explain the evolution of the Late Precambrian (Brasiliano Cycle) terranes of the NE of the State of Sao Paulo and the adjacent areas of the State of Minas Gerais, domain of the Guaxupe Massif, SE Brazil, are presented and discussed. The models can be classified in: 1) classic; 2) mainly ensialic; and 3) applications of the plate tectonic theory. -from English summary

Tectonic setting and U/Pb zircon dating of the plutonic Socorro Complex in the Transpressive Rio Paraíba do Sul Shear Belt, SE Brazil

The Precambrian Rio Paraíba do Sul Shear Belt comprises a 200-km-wide anastomosing network of NE-SW trending ductile shear zones extending over 1000 km of the southeastern coast of Brazil. Granulitic, gneissic-migmatitic, and granitoid terrains as well as low- to medium-grade metavolcanosedimentary sequences are included within it. These rocks were affected by strong contractional, tangential tectonics, due to west-northwestward oblique convergence of continental blocks. Subsequent transpressional tectonics accomodated large dextral, orogen-parallel movements and shortening. The plutonic Socorro Complex is one of many deformed granites with a foliation subparallel to that of the shear belt and exposes crosscutting relationships between its tectonic, magmatic, and metamorphic structures. These relationships point to a continuous magmatic evolution related to regional thrusts and strike slip, ductile shear zones. The tectonic and magmatic structural features of the Serra do Lopo Granite provide a model of emplacement by sheeting along shear zones during coeval strike-slip and cross shortening of country rocks. Geochronological data indicate that the main igneous activity of Socorro Complex spanned at least 55 million years, from the late stage of the northwestward ductile thrusting (650 Ma), through right-lateral strike slip (595 Ma) deformation. The country rocks yield discordant age data, which reflect a strong imprint of the Transamazonian tectono-metamorphic event (1.9 to 2.0 Ma). We propose a model for the origin of calcalkaline granites of the Ribeira Belt by partial melting of the lower crust with small contributions of the lithospheric mantle during transpressional thickening of plate margins, which were bounded by deep shear zones. The transpressional regime also seems to have focused granite migration from deeper into higher crustal levels along these shear zones.

Mapeamento do contorno estrutural do embasamento da bacia sedimentar de Curitiba - PR

The sedimentary Curitiba basin is located in the Central-Southern part of the first Parananense plateau, and comprises Curitiba (PR), and part of the neighbour Municipalities (fig.1). It is supposed to be of Plio-Pleistocene age. It has a shallow sedimentary fulfillment, represented by the Guabirotuba formation (BIGARELLA and SALAMUNI, 1962) which is dristributed over a large area of about 3.000km2. The internal geometry, not entirely known yet, is actually object of detailed research, that shows its geological evolution to Cenozoic tectonic movements. For the purpose of this study the definition of the structural contour of the basement and their depo-centers is fundamental. This paper presents the results of the integration of surface and subsurface data, processed by statistical methods, which allowed a more precise definition of the morphostructural framework of the basement. For the analysis of the geological spacial data, specific softwares were used for statistical processing for trend surfaces analysis. The data used in this study are of following types: a) drilling logs for ground water; b) description of surface points of geological maps (CRPM, 1977); c) description of points of geotechnical drillings and down geological survey. The data of 223 drilling logs for ground water were selected out of 770 wells. The description files of 700 outcrops, as well as planialtimetric field data, were used for the localization of the basement outcrop. Thus, a matrix with five columns was set up: utm E-W (x) and utm N-S (y); surface altitude (z); altimetric cote of the contact between sedimentary rocks and the basement (k); isopachs (l). For the study of the basement limits, the analysis of surface trends of 2(nd) and 3(rd) degree polinomial for the altimetric data (figs. 2 and 3) were used. For the residuals the method of the inverse of the square of the distance (fig.4) was used. The adjustments and the explanations of the surfaces were made with the aid of multiple linear regressions. The analysis of 3rd degree polinomial trend surface (fig.3) confirmed that the basement tends to be more exposed towards NNW-SSE explaining better the data trend through an ellipse, which striking NE-SW and dipping SW axis coincides with the trough of the basin observed in the trending surface of the basement. The performed analysis and the respective images offer a good degree of certainty of the geometric model of the Curitiba Basin and of the morphostructure of its basement. The surface trend allows to sketch with a greater degree of confidence the structural contour of the topgraphic surface (figs. 5 and 6) and of the basement (figs. 7 and 8), as well as the delimitation of intermediate structural heights, which were responsible for isolated and assymmetric depocenters. These details are shown in the map of figures 9 and 10. Thus, the Curitiba Basin is made up by a structural trough stretching NE-SW, with maximum preserved depths of about 80m, which are separated by heights and depocenters striking NW-SE (fig. 11). These structural features seems to have been controlled by tectonic reactivation during the Tertiary (HASUI, 1990) and which younger dissection was conditioned by neotectonic processes (SALAMUNI and EBERT, 1994).