U-Pb geochronology of the southern Brasília belt (SE-Brazil): Sedimentary provenance, Neoproterozoic orogeny and assembly of West Gondwana

The Brasília belt borders the western margin of the São Francisco Craton and records the history of ocean opening and closing related to the formation of West Gondwana. This study reports new U-Pb data from the southern sector of the belt in order to provide temporal limits for the deposition and ages of provenance of sediments accumulated in passive margin successions around the south and southwestern margins of the São Francisco Craton, and date the orogenic events leading to the amalgamation of West Gondwana. Ages of detrital zircons (by ID-TIMS and LA-MC-ICPMS) were obtained from metasedimentary units of the passive margin of the São Francisco Craton from the main tectonic domains of the belt: the internal allochthons (Araxá Group in the Áraxá and Passos Nappes), the external allochthons (Canastra Group, Serra da Boa Esperança Metasedimentary Sequence and Andrelândia Group) and the autochthonous or Cratonic Domain (Andrelândia Group). The patterns of provenance ages for these units are uniform and are characterised as follows: Archean- Paleoproterozoic ages (3.4-3.3, 3.1-2.7, and 2.5-2.4Ga); Paleoproterozoic ages attributed to the Transamazonian event (2.3-1.9Ga, with a peak at ca. 2.15Ga) and to the ca. 1.75Ga Espinhaço rifting of the São Francisco Craton; ages between 1.6 and 1.2Ga, with a peak at 1.3Ga, revealing an unexpected variety of Mesoproterozoic sources, still undetected in the São Francisco Craton; and ages between 0.9 and 1.0Ga related to the rifting event that led to the individualisation of the São Francisco paleo-continent and formation of its passive margins. An amphibolite intercalation in the Araxá Group yields a rutile age of ca. 0.9Ga and documents the occurrence of mafic magmatism coeval with sedimentation in the marginal basin. Detrital zircons from the autochthonous and parautochthonous Andrelândia Group, deposited on the southern margin of the São Francisco Craton, yielded a provenance pattern similar to that of the allochthonous units. This result implies that 1.6-1.2Ga source rocks must be present in the São Francisco Craton. They could be located either in the cratonic area, which is mostly covered by the Neoproterozoic epicontinental deposits of the Bambuí Group, or in the outer paleo-continental margin, buried under the allochthonous units of the Brasília belt. Crustal melting and generation of syntectonic crustal granites and migmatisation at ca. 630Ma mark the orogenic event that started with westward subduction of the São Francisco plate and ended with continental collision against the Paraná block (and Goiás terrane). Continuing collision led to the exhumation and cooling of the Araxá and Passos metamorphic nappes, as indicated by monazite ages of ca. 605Ma and mark the final stages of tectonometamorphic activity in the southern Brasília belt. Whilst continent-continent collision was proceeding on the western margin of the São Francisco Craton along the southern Brasília belt, eastward subduction in the East was generating the 634-599Ma Rio Negro magmatic arc which collided with the eastern São Francisco margin at 595-560Ma, much later than in the Brasília belt. Thus, the tectonic effects of the Ribeira belt reached the southernmost sector of the Brasília belt creating a zone of superposition. The thermal front of this event affected the proximal Andrelândia Group at ca. 588Ma, as indicated by monazite age. The participation of the Amazonian craton in the assembly of western Gondwana occurred at 545-500Ma in the Paraguay belt and ca. 500Ma in the Araguaia belt. This, together with the results presented in this work lead to the conclusion that the collision between the Paraná block and Goiás terrane with the São Francisco Craton along the Brasília belt preceded the accretion of the Amazonian craton by 50-100 million years. © 2003 Elsevier B.V. All rights reserved.

Structural and geochronological studies of the Médio Coreaú domain, NE Brazil: Constraints on Brasiliano/Pan-African tectonic evolution in the NW part of the Borborema Province

Recent structural investigations and geochronological studies of rocks from the Médio Coreaú domain in the NW part of northeast Brazil's Borborema Province provide important constraints on the tectonic evolution of the region both preceeding and during the assembly of West Gondwana. Field observations of structural features and fabrics have revealed the presence of four distinct deformational phases in the MCD: D1, D2, D3 and D4. Only the early Paleoproterozoic gneisses record the D1 tectonic event and its preservation is cryptic owing to strong overprinting by the subsequent tectonic phases. The D2, D3 and D4 events affected younger supracrustal rocks and Neoproterzoic magmatic units, and U-Pb geochronological constraints show that all of these tectonic phases represent deformational events that occurred during Brasiliano collision between the West African craton and the NW part of the Borborema Province. The D2 phase, lasting between ca. 622 and 591 Ma, represents a frontal collision stage, which generated NW verging thrust-nappe systems, low-angle foliation, high-grade metamorphism and crustal anatexis. Transition to a strike-slip regime (D3) occurred at around 591 Ma when the region entered a phase of escape tectonics. During this time, the motion of crustal blocks towards NE and E was accommodated along numerous anastomosing shear zones. Syntectonic emplacement of granitoid plutons took place in transtensional domains of the shear zone system. The intrusion of late tectonic granitoids and rapid uplift and cooling of the orogen around 560 Ma as a result of D4 transpressional movements marked the end of the D3 transcurrent regime. These findings show that only the early Paleoproterozoic gneisses in the Médio Coreaú domain are polycyclic in nature. Rather than representing distinct orogenic events, the D2, D3 and D4 tectonic phases are a manifestation of progressive deformational events that developed in response to changes in the regional stress field during convergence and collision between the Borborema Province and its surrounding cratons.

Os granitóides brasilianos da faixa de dobramentos paraguai, MS e MT

The Brazilian Granitic Province from southeastern Mato Grosso do Sul and Mato Grosso region, central western Brazil, can be divided into two major groups and/or magmatic events related to the evolution of the Paraguay Fold Belt. The southern portion crops out in Mato Grosso do Sul State and is constituted by the Taboco, Rio Negro, Coxim and Sonora massifs forming NE-SW oriented, elongated small intrusions. The north portion crops out in Mato Grosso State and is constituted by the São Vicente, Araguaiana and Lajinha batholiths. Lithogeochemical aspects of the northern granites point to Type-I granites ranging from K calc-alkaline to high-K, peraluminous to metaluminous in composition, generated in an environment of continental collision and/or post- collision decompression. The southern granites are Type-I, from K calc-alkaline to high-K, peraluminous to subordinate metalummous, in a syn-collision continental arc environment with the exception of some pre-collisional facies from the Rio Negro Massif. The southern granites have less SiO 2 and K 2O, and are less differentiated and evolved than granites from the northern region. The four southern granites can be grouped into two subordinate sets with the degree of differentiation increasing from South (Taboco and Rio Negro) to North (Coxim and Sonora). The granitic rocks are characterized by a magmatism generated by melting of material from the lower crust which suggests that in this province the formation from non-cogenetic magmas with diversified compositions and distinct degrees of fractioning reaching more steady consolidated environments at the end of the collisional event in the southeastern Amazonian Craton.

Contexto tectônico dos granitóides neoproterozóicos da faixa de dobramentos paraguai, MS e MT

The Neoproterozoic Granitic Province from the southeast of Mato Grosso and Mato Grosso do Sul region is constituted by seven distinctive granitic bodies, emplaced in the epimetamorphic rocks of the Cuiabá Group and related to the evolution of Paraguai Folded Belt. The Northern portion crops out in Mato Grosso State and is constituted by São Vicente, Araguaiana and Lajinha batholiths; the Southern portion crops out in the Mato Grosso do Sul State and is represented the Sonora, Coxim Rio Negro and Taboco massifs. The structural evolution is evidenced by the presence of three deformational phases, the first one is characterized by axial planar foliation (S 1), parallel or sub parallel to S 0, with attitude N60E/70NW; the second constitutes the most important phase for the tectonic arrangement and is defined by a slaty and/or crenulation cleavages (S 2), with attitude N10W/30SW and contact metamorphism associated to the emplacement of granitic bodies, the third phase is characterized by a weak retrometamorphic cleavage (S 3) with attitude N10E/ 80NW, that evolves local and gradually to strike-slip shear zones. The geological data suggest that this province was formed syn- to post tectonic to the D2 deformational set associated to the end of the collisional event in the Southeastern of the Amazonian Craton.

Dose de exposição radiométrica de granitos do estado de Rondônia, Brasil

This work evaluated the activity concentration of the radioelements K, eU and eTh in samples of granites from Rondônia State, Brazil. The statistical analysis of the data indicated that they fit lognormal distributions. The modal values correspond to about 11% for K, 29 ppm for eU and 85 ppm for eTh. Directsignificant correlations were found among the concentrations of the three radioelements, i.e. r = 0.71 (between K and eU), r = 0.72 (between K and eTh), andr = 0.72 (between eU and eTh), suggesting congruency of their accumulation in minerals occurring in the rocks analyzed. The activity concentration data allowed estimate the absorbed dose rate in air at 1 m above the ground, which also fits a lognormal distribution characterized by a mode of 2.7 mSv/y that is slightly higher than the average worldwide exposure of 2.4 mSv/y. The results obtained also allowed evaluate if the granites analyzed are radiometrically suitable as building and ornamental materials. © 2009 Sociedade Brasileira de Geofísica.

Geocronologia do maciço Granítico Sararé no SW do Cráton Amazônico

Sararé Massif occurs in the southwest Mato Grosso state intruded into Mesoproterozoic units of the Jauru Block inside the Amazonian Craton. It presents an extension of approximately 80 km2 and NW-SE tectonic structures control the elongated shape. It is constituted by three major monzogranitic petrographic facies, represented by leucocratic, reddish, isotropic, equi-inequigranular to locally porphyritic rocks. The composition indicates S-type, peraluminous, with indicatives of late- to post-kinematic magmatism. Geochronological studies with 40Ar/39Ar in biotites and muscovites resulted in ages of 903 to 906 Ma was interpreted as massif rocks cooling period and U-PB 917 ± 18 Ma. ages points to the crystallization of the intrusive body. The massif is formed by melting of material of the upper crust, in an environment of continental collision and/or of post-collisional decompression at the ending of the Aguapeí-Sunsás event, in more stable environments of consolidation and tectonic stabilization of the Amazonian Craton.

Estudo geofísico de vazamento de combustíveis em posto de abastecimento

The geoelectrical methods have been widely used in research involving the evaluation and monitoring of areas with environmental risk. This paper presents the results of applying the Electrical Resistivity method by electrical profiling technique to investigate the fuel presence in soil and groundwater proceeding in station gas, located in an urban area Caçapava do Sul (RS), on soil in situ, from modification of Caçapava granite. The results suggest an association between low resistivity anomalies zone with potentially degraded from underground tanks worthless on the form of free phase, now represented as residual phase. The results of the model inversion are consistent with the standards expected for hydrocarbons present in the saturated zone. The electrical resistivity method proved to be an important tool for assessment and environmental monitoring in conjunction with direct methods of investigation.

Caracterização Tecnológica das Rochas Ornamentais do Maciço Capão Bonito, SP

The Capão Bonito Granitic Massif is situated in the south portion of the São Paulo State and represents an elongate body with general direction NE-SW, intrusive in epimetamorphic rocks of Açungui Group (Votuverava Formation), and in granitic rocks of the Três Córregos Complex. It is partially covered by sedimentary rocks of the Paraná Basin (Itararé Group). As the chief type we have red sienogranite, holo to leucocratic with biotite and rare hornblende, inequigranular with medium to coarse grains to porphiritic and isotropic to slightly cataclastic textures of marginal zones. This granite was analyzed for petrographics (composition, structure and texture), chemical composition (major elements), physical and mechanical (water absorption, resistance to abrasion, impact of hard body and efforts of compression and traction) and chemical attack aspects. The results were compared to suggested values for granitic rocks used for ornamental purposes. The whole massif shows compositional, textural, structural (related to isotropy) and chemical (major elements) characteristics very homogeneous. The varieties of sienogranite named commercially as Capão Bonito or Rubi Red Granite showed results very similar to each other, with some variations in the physical and mechanical resistance resulting of the penetrative brittle deformation of regional occurrence, evidenced by differences in the microfissural index.

Suíte plutônica Alumiador, grupo Amonguijá, maciço rio apa - MS

The Rio Apa Massif corresponds the southern portion of the Amazon Craton and is located in the southwest of Mato Grosso do Sul State. It consists on Paleoproterozoic rocks of Rio Apa Complex, Alto Tererê Group and Amonguijá Group, is subdivided into Alumiador Plutonic Suite and Serra da Bocaina Volcanic Suite. The volcanic suite is comprises sub volcanic, volcanic and varied volcanoclastics rocks with composition ranging from alkali-rhyolitic to rhyolite types. The plutonic suite corresponds to an N-S elongated batholith and is characterized by four main segments delimited by NW-SE faults. The southern and central main segments, discussed in this paper, are characterized by the following petrographic facies: medium to fine grained hornblende-biotite monzogranites, coarse grained biotite monzogranites, graphic biotite sienogranites and muscovite sienogranites and the northern segment is contemporaneous and is composed of two different sequences of rocks, one acid and another of basic to ultrabasic composition. The southern and central segment consists of to chemically compatible rocks with the types I and A Granites. These are calc-alkaline rocks of high potassium to the shoshonitic and subalkaline. Constitute sin-collisional granites of metaluminous the peraluminous characters of the Amonguijá Magmatic Arc, but they exhibit late litotypes with chemical characteristics of post tectonic granites from intraplate environment.

Relação do meio físico com o manejo sustentável de plantio de eucalipto em áreas de terrenos acidentados - A Fazenda Santa Edwirges, Vale do Paraíba, Sudeste do Brasil

This study intends to evaluate the effects of landscape physical elements (rocks and relief) associated with silviculture activities. The study was carried out on a small farm (Fazenda Santa Edwirges) covered by Eucalyptus forested situated in the Paraiba do Sul Basin, Southeast Brazil. The methodology consisted of detailed geological and geomorphological studies at 1:10,000 scale, and laboratory analysis of soil physical properties. The results showed three geologic-geomorphologic associations (ridge escarpment with granitic rocks, steep and gentle hills cut by shear zones and gentle hill with alluvial sediments) present high vulnerability for the development of the physical processes such as accelerated erosion landslides and flooding. In contrast, mountains associated with gneissic rocks present smaller vulnerability and high resilience for the development of the physical processes. The results have showed the importance of considering the interactions among landscape physical for the eucalyptus forest management contributing to a better selection area for eucalyptus cultivation and minimize adverse environment impact in road design.

Radon emissions related to the granitic Precambrian shield in southern Brazil

The equivalent uranium (eU) activity concentration was analysed in selected granite samples at several sites in Porto Alegre, Southern Brazil, to obtain information on the radon (222Rn) generation by the aquifer rock matrices. Radon analyses of ground water and soil samples were also performed. Several samples exhibited a dissolved 222Rn activity concentration exceeding the World Health Organization maximum limit of 100 Bq l-1. The dissolved radon content in ground waters from the Fractured Precambrian Aquifer System exhibited a direct significant correlation with the eU in the rock matrices, which is a typical result of water-rock interactions. Variation in the soil's porosity was confirmed as an important factor for 222Rn release, as expected, due to its gaseous nature. Thus, although the calcic-alkaline to alkaline Precambrian granitoid rocks of the study area are important reservoirs for underground resources, they can release high amounts of radon gas into the liquid phase. © 2013 Copyright Taylor and Francis Group, LLC.

Correlação entre propriedades petrográficas e comportamento tecnológico e de alterabilidade das rochas ornamentais silicáticas Diamante Negro (BA), Ocre Itabira e Banco Galaxy (ES)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Geologia estrutural aplicada às rochas ornamentais na Pedreira Knawa, Cláudio (MG)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Geologia e mineralogia de pegmatito mineralizado em estanho e metais associados (Nb, Ta, Zn, Cu, Pb), Mina Bom Futuro, Rondônia

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Caracterização petrológica, geoquímica e geocronológica (U/Pb e Ar/Ar) do maciço sararé Nova Lacerda-MT

Pós-graduação em Geologia Regional - IGCE