Jean Michel Legrand

Finite-element simulation of laminar swirling decaying flow induced by means of a tangential inlet in an annulus

Abstract This work is dedicated to the numerical modeling of hydrodynamics of an annular swirling decaying flow induced by means of a single tangential inlet in laminar flow regime. Complete Navier-Stokes equations have been solved by a finite element method using the FIDAP package. We have shown that a correct numerical modeling is strongly linked to the mesh generation, the design of which is crucial. Indeed, the tangential inlet induces recirculating flows, whose shapes and sizes are intimately depending on both the axial location from the swirl generator and the azimuthal position with respect to the tangential inlet axis. The swirl decay along the flow path has been characterized using various profiles of both tangential and axial velocity components, streamlines angles and local swirl intensity near both cylinders of the annulus. The mean swirl intensity in the whole annular gap thickness has been found to decrease exponentially from the entrance section.

Northwestern Overthrusting and Related Lateral Escape During the Brasiliano Orogeny North of the Patos Lineament, Borborema Province, Northeast Brazil

The Borborema province (BP) of northeastern Brazil, located between the Sao Luis and Sao Francisco cratons, represents a branching system of Precambrian orogens of the South American platform. It is composed of segments of Archean and Proterozoic crust that were deformed by the convergence of the West African and Sao Francisco-Congo cratons during assembly of the Brasiliano collage (650 to 500 Ma), a period of intense orogenic activity considered to be the strongest and most pervasive tectonic event that affected the Precambrian of the South American platform. The tectonic and kinematic history of the Brasiliano/Panafrican orogeny is fundamental for reconstructing South American and African Precambrian geology. The correlation between Neoproterozoic tectonic processes occurring in both continents should use structural elements, of regional or local character, with identical kinematic and metamorphic conditions manifested in both basement and supracrustal units. North of the Patos shear zone, subhorizontal...

U-Pb e Sm-Nd em Ortognaisses Riacianos e Estaterianos nos Terrenos Rio Piranhas-Seridó e Jaguaribeano, Província Borborema, Brasil

A zona de cisalhamento Portalegre separa os terrenos geologicos Rio Piranhas-Serido e Jaguaribeano do Dominio Setentrional da Provincia Borborema, com gnaisses bandados dos Complexos Caico e Jaguaretama representando os respectivos embasamentos destes terrenos. Analises U-Pb forneceram idades de 2.193 ± 16 Ma para os ortognaisses do Complexo Jaguaretama, resultados muito similares as determinadas para o Complexo Caico. Idades T DM Sm-Nd nesses Complexos forneceram valores neoarqueanos (ca. 2,5 Ga), com eNd(t) muito proximos ao CHUR. Intrudindo as rochas do Complexo Jaguaretama, destacam-se corpos alongados, foliados e com porfiros estirados, denominados de Suite Serra do Deserto. Estes forneceram idades de cristalizacao a 1.777 ± 8 Ma, ratificando um periodo extensional que ocorreu no Estateriano, bem representado no terreno Jaguaribeano por sequencias vulcanossedimentares e plutonicas Tipo-A. Augen gnaisses com texturas similares, denominados de Suite Poco da Cruz, sao encontrados intrudindo o Complexo Caico no terreno Rio Piranhas-Serido, porem, as idades registradas por todo este dominio sao predominantemente Riacianas (ca. 2,2 Ga) e de afinidades calcio-alcalinas, indicando que estes augen gnaisses possuem diferentes assinaturas e estao bem separados no tempo. Alem disso, alem dos dados geofisicos previos que sugerem esta divisao de Terrenos marcada pela Zona de Cisalhamento Portalegre, os Complexos Caico e Jaguaretama exibem diferencas composicionais marcantes. Corpos de anfibolitos alongados e concordantes a subconcordantes com o bandamento do Complexo Caico e importante contribuicao sedimentar na constituicao do Complexo Jaguaretama com importantes intercalacoes de marmores sao algumas destas diferencas.

Sistema Sm-Nd em rocha-total aberto versus fechado: comportamento isotópico em zonas de alta deformação

High strain shear zones of Brasiliano age, developed in Paleoproterozoic basement gneiss of the Caico region, Borborema Province, NE Brazil, were associated with medium- to low-grade metamorphism and deformational processes that transformed porphyritic augen gneiss into muscovite quartzite, modifying their original mineralogy and chemical properties. During the last hydrothermal event mobility of major, minor and trace elements was great, whereas the pattern of Rare Earth Elements was not changed. We carried out a Sm-Nd isotopic study in these rocks in order to understand the behavior of Nd isotopes during mylonite generation. T DM model ages at around 2.6 Ga and µNd (t) values for both protolith and transformed rock suggest that the Nd isotopic system remained closed, recording the original source rock signature, despite undergoing two superposed metamorphic events.These new Sm-Nd results provide important information on the geologic evolution of basement rocks in the central Rio Grande do Norte Terrane of the Borborema Province, NE Brazil.