Shear wave splitting in SE Brazil: an effect of active or fossil upper mantle flow, or both?

International audienceWe investigated the structure of the upper mantle beneath southeastern Brazil using teleseismic shear wave splitting measurements. Measurements were performed on seismic data recorded in the Ribeira and Brasilia Neoproterozoic belts, which wrap around the southern termination of the São Francisco craton and disappear westward under the Paraná basin. In the northern Ribeira belt, dominated by thrust tectonics, the fast shear wave polarization planes trend on average N080°E, whereas in the central domain, dominated by strike-slip tectonics, fast shear waves are polarized parallel to the structural trend (N065°E). Stations located above the main transcurrent fault display large delay times (> 2.5 s). Such values, among the largest in the world, require either an unusually large intrinsic anisotropy frozen within the lithosphere, or a contribution from both the lithospheric and asthenospheric mantle. Within the southern Brasilia belt, fast split shear waves are polarized parallel to the structural trend of the belt, at a high angle from the APM. Although part of our data set strongly favors an origin of anisotropy related to a fabric frozen in the lithospheric mantle since the Neoproterozoic, a contribution of the asthenospheric flow related to the present day plate motion is also required to explain the observed splitting parameters

EBSD-measured lattice-preferred orientations and seismic properties of eclogites

International audienceWe investigated the deformation mechanisms and the seismic properties of 10 eclogite samples from different localities (Alps, Norway, Mali and eastern China) through the analysis of their microstructures and lattice-preferred orientations (LPO). These samples are representative of various types and intensity of deformation under eclogitic metamorphic conditions. Omphacite and garnet LPO were determined from electron backscatter diffraction (EBSD) technique. Garnet appears to be almost randomly oriented whereas omphacite develops strong LPO, characterized by the [001]-axes concentrated sub-parallel to the lineation, and the (010)-poles concentrated sub-perpendicular to the foliation. In order to analyze the deformation mechanisms that produced such omphacite LPO, we compare our observations to LPO simulated by viscoplastic self-consistent numerical models. A good fit to the measured LPO is obtained for models in which the dominant slip systems are 1/2h110i{11 ¯ 0}, [001] {110} and [001] (100). Dominant activation of these slip systems is in agreement with TEM studies of naturally deformed omphacite. Seismic properties of eclogite are calculated by combining the measured LPO and the single crystal elastic constants of omphacite and garnet. Although eclogite seismic anisotropies are very weak (less than 3% for both P-and S-wave), they are generally characterized by a maximum P-wave velocity sub-parallel to the lineation and by a minimum velocity approximately normal to foliation. The mean P-and S-wave velocities are high (respectively, 8.6 and 4.9 km/s). The S-wave anisotropy pattern displays complex relationships with the structural frame but the fast polarization plane generally tends to be parallel to the foliation. Calculated reflection coefficients show that an eclogite/crust interface is generally a good reflector (Rc > 0.1), whereas an eclogite body embedded in the upper mantle would be hardly detectable

Aspectos Geoquímicos de Silicificações em Rochas Sedimentares no Rio Grande do Sul, Brasil

Some exposures of silicified sedimentary rocks and duricrusts occur in the central Depressão Periférica along the edge of the Paraná Basin in Rio Grande do Sul State, in southern part of Brazil. These silicified materials were firstly studied in the petrographic aspects by Silvério da Silva & Menegotto (2002). This paper presents geochemical results of the analysis on samples of sedimentary rocks and silica duricrusts collected in two profiles (Santa Maria and Cachoeira do Sul). The relationships between the sedimentary rocks and the duricrusts, as well their probable provenance and genesis, are discussed. Silicification occurs as lenses, concretions, nodules and pedotubules, in the Mesozoic sedimentary rocks of these profiles. Micro quartz predominates and forms the most part of the matrix. Fibrous chalcedony and mega quartz were present in minor amounts filling vughs. Three types of silicification were recognized: silcretes (SiO2>87%), silica rich concretions (SiO2 from 76.10 % to 86.76% SiO2) and sedimentary rocks with few silica cement. Gresen′s mass balance is presented to point out the gain of SiO2. The silica source is related to weathering processes of the minerals of the sedimentary rock and added to the groundwater.Some exposures of silicified sedimentary rocks and duricrusts occur in the central Depressão Periférica along the edge of the Paraná Basin in Rio Grande do Sul State, in southern part of Brazil. These silicified materials were firstly studied in the petrographic aspects by Silvério da Silva & Menegotto (2002). This paper presents geochemical results of the analysis on samples of sedimentary rocks and silica duricrusts collected in two profiles (Santa Maria and Cachoeira do Sul). The relationships between the sedimentary rocks and the duricrusts, as well their probable provenance and genesis, are discussed. Silicification occurs as lenses, concretions, nodules and pedotubules, in the Mesozoic sedimentary rocks of these profiles. Micro quartz predominates and forms the most part of the matrix. Fibrous chalcedony and mega quartz were present in minor amounts filling vughs. Three types of silicification were recognized: silcretes (SiO2>87%), silica rich concretions (SiO2 from 76.10 % to 86.76% SiO2) and sedimentary rocks with few silica cement. Gresen′s mass balance is presented to point out the gain of SiO2. The silica source is related to weathering processes of the minerals of the sedimentary rock and added to the groundwater

Análise estrutural do Grupo Rio Pardo: sudeste do Estado da Bahia

O Grupo Rio Pardo esta localizado no sudeste do Estado da Bahia e geologicamente, marca a transição entre o Cráton do São Francisco e a Faixa Araçuaí. Trata-se de uma sequência metassedimentar de baixo grau metamórfico, de idade meso a neoproterozoica, depositadas sobre um embasamento de idade paleoproterozoica a arqueana. O Grupo Rio Pardo é constituído das seguintes unidades litoestratigráficas, da base para o topo: Formação Panelinha formada por metapsefitos e metagrauvacas; Subgrupo Itaimbé, compreendendo as Formações Camacã (metapelitos e lentes carbonáticas), Água Preta (metarenitos e metassiltitos), Serra do Paraíso (metacarbonatos e quartzitos) e Santa Maria Eterna (metacarbonatos e quartzitos). No topo desta sequência, discordantemente sobre as anteriores, depositou-se a Formação Salobro, constituída de metapelitos e metapsefitos. O Grupo Rio Pardo esta dividido em duas unidades litoestruturais, separadas pela falha inversa Rio Pardo-Água Preta com transporte tectônico para nordeste. A Unidade Litoestrutural 1, que abrange o setor norte, possui características autóctones com estruturas associadas à primeira fase de deformação. A Unidade Litoestrutural 2, localizada a sudoeste da falha inversa, caracteriza um bloco subautóctone com dobramentos fechados relacionados à segunda fase de deformação. Um terceiro evento deformacional esta registrado na borda oeste da bacia. A vergência tectônica do Grupo Rio Pardo para NE se explica pela mudança do regime deformacional e da orientação dos eixos principais da deformação no decorrer do evento orogênico colisional brasiliano no setor norte da faixa Araçuaí, onde o transporte tectônico para norte serviu de motor para a deformação no Grupo Rio Pardo.The Meso- to Neoproterozoic Rio Pardo Group is located in the southeastern region of the Bahia State and consists of low-grade metasedimentary rocks deposited on Paleoproterozoic to Archean basement. From the base to the top, the metasedimentary rocks are grouped into the following sequences: Panelinha Formation consisting of coarse-grained immature clastics; the overlying Itaimbé Subgroup which is made up of the Camacã Formation (metapelites with local carbonates), the Água Preta Formation (fine-grained metapsamites and local carbonate lenses), Serra do Paraíso Formation (metacarbonates and quartzites) and the Santa Maria Eterna Formation (metaconglomerates and metacarbonates). The Salobro Formation was deposited unconformably on this sequence and consists of coarse-grained immature and local finegrained clastic rocks. The Rio Pardo Group was affected by three successive folding events, which were recorded in two litho-structural units. The litho-structural unit 1 is located in the northeastern part of the basin, and the litho-structural unit 2, in the southwestern part of the basin. These units are separated by the Rio Pardo-Água Preta inverse fault, trending NW-SE and dipping SW. The first unit is autochthonous and monophasic and displays open folds and slaty cleavage, changing gradually towards southwest into large overturned folds with axial plane schistosity. The second unit is polyphasic and shows large folds with NE vergence. A third folding is represented by folds and foliations present at the western margin of the basin. The NE vergence of the Rio Pardo Group can be explained by changes in the deformation regime and in the direction of the principal axis of deformation in the north sector of the Araçuaí belt during the Brasiliano collision orogen. The tectonic transport to the north could be the cause of deformation of the Rio Pardo Group

Tendinopathy of the anterior compartment of the ankle

OBJETIVO: Análise retrospectiva da etiopatogenia, diagnóstico e opções de tratamento nos casos de tendinopatias do compartimento anterior do tornozelo (TCAT). MÉTODO: No período de setembro de 1998 a fevereiro de 2009, 13 pacientes foram operados por tendinopatia do compartimento anterior do tornozelo. A casuística constou de 10 pacientes do sexo masculino e três do feminino. O lado direito foi acometido em 12 pés e um do esquerdo. A média de idade foi de 35 anos (15-67). A etiologia foi traumática em oito pacientes e em cinco, degenerativa (atraumática). O tempo médio do diagnóstico ao tratamento foi de 19 meses (1-60) e o seguimento foi de 34 meses (4-127). O diagnóstico foi feito através da história e exame clínico. A ressonância magnética foi realizada em nove pacientes para estadiamento e planejamento. O tratamento cirúrgico foi personalizado para cada caso (sinovectomia, ressecção de ventre muscular, solidarização com o tendão adjacente e enxerto livre de tendão semitendíneo). Para a avaliação dos resultados foram utilizadas as escalas: 1) graduação subjetiva de satisfação, 2) AOFAS e 3) Maryland. RESULTADO: Em relação à escala de graduação subjetiva de satisfação, 12 pacientes satisfeitos e um paciente insatisfeito. A média da escala AOFAS foi de 80 pontos, a média da escala Maryland foi de 86 pontos. CONCLUSÃO: O tratamento cirúrgico é eficaz para recuperação funcional. As técnicas cirúrgicas devem ser personalizadas. A opção do enxerto livre de tendão semitendíneo é eficiente nas falhas maiores que cinco centímetros.OBJECTIVE: To carry out a retrospective analysis of the etiopathogeny, diagnosis and therapeutic options in cases of tendinopathies of the anterior compartment of the ankle. METHOD: 13 patients underwent surgery between September 1998 and February 2009; ten men and three women. The right side was involved in twelve patients and the left in one. The averaging age was 35 years of age (15-67). The etiology was traumatic in eight patients and degenerative (non-traumatic) in five. The average time to diagnosis was 19 months (1 - 60) and the average follow-up time was 34 months (4 - 127). The diagnosis was made by anamnesis and clinical findings. Magnetic resonance imaging was performed in nine patients, for staging and planning. The surgical treatment was personalized in each case (debridement, resection of the muscle, grafting with the adjacent tendon, and free graft of the semitendinosus tendon). The following scales were used for the evaluation: 1) subjunctive satisfaction scale, 2) AOFAS and 3) Maryland. RESULTS: In relation to the subjective satisfaction scale, 12 patients were satisfied and one was dissatisfied. The average AOFAS scale was 80 points, and the average Maryland scale was 86 points. CONCLUSION: Surgical treatment is effective for restoring function. The surgical techniques must also be personalized. The free graft of the semitendinosus tendon option is effective for gaps larger than five centimeters

Capacitor Cilíndrico Excêntrico

Uhuru is an African American student publication that ran from Fall 1977 through February 1980. Articles cover campus and current events from an African American perspective. The newsletter contains information on BATU, meeting minute briefs, brief campus news, historical facts, interviews with prominent black figures, and sports information.https://ecommons.udayton.edu/uhuru/1008/thumbnail.jp

Avaliação preliminar dos argilominerais das folhas de Camobi e Santa Maria, Rio Grande do Sul

O trabalho não apresenta resumo

Idades Rb-Sr das rochas da região de Bananal - SP

Este trabalho apresenta novos dados geocronológicos Rb-Sr, em rocha total, dos principais tipos litológicos da região limítrofe dos estados de São Paulo e Rio de Janeiro, no contexto da Serra do Mar, com o objetivo de caracterizar a seqüência de eventos geológicos e as possíveis relações entre as rochas presentes. Os paragnaisses, predominantes na região, os núcleos ortognáissicos, considerados como embasamento da seqüência paraderivada, e os leucogranitos, injetados em ambos, forneceram diagramas isocrônicos que convergem para uma época ao redor de 700 Ma, interpretada como o processo metamórfico gerador das rochas gnáissicas, o qual também propiciou, através de fusão parcial, a formação dos leucogranitos. A proximidade dos pontos relativos a estas litologias, no diagrama de evolução do Sr, reforça esta consideração. Como representante dos granitos ambientados tectonicamente em expressivas zonas de cisalhamento dúcteis, relativamente comuns na região, o granito Getulândia, analisado radiometricamente, forneceu a idade de 514 Ma, se enquadrando entre os corpos graníticos tardi-tectônicos relacionados ao Ciclo Brasiliano tardio, que se estendeu até o Cambriano Médio.New Rb/Sr whole rock isochron ages have been determined for the main lithological units that occur in São Paulo and Rio de Janeiro States. These rocks belong to the "Serra do Mar" domain. The purpose of mis work is to characterize the sequence of the geological events as well as the possible relationship between the different rocks. The geochronological data suggest that the paragneisses and the basement rocks, represented by orthogneiss nuclei, were generated under amphibolite conditions around 700 Ma. At the same time the leucogranites were generated by partial melting processes and injected into both gneiss types. Tarditectonic granitic magmatic activities took place within ductile shear zones. One of the granites, the Getulândia granite, yielded an age of 514 Ma, falling in the range of the late Brasiliano Cycle which extended into the Middle Cambrian