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Tectônica rúptil aplicada ao estudo de aqüífero em rochas cristalinas fraturadas na região de Cotia, SP; Brittle tectonics applyed to study of crystalline fractured-bedrock aquifer in Cotia, SP region

Alves, Fernando Machado
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 19/08/2008 Português
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O estudo da hidrogeologia em aqüífero cristalino fraturado apresenta como maior desafio a imprevisibilidade do meio, uma vez que o fluxo ocorre exclusivamente pelas fraturas. Neste sentido informações de atitude, abertura e conectividade de fraturas tornam-se essenciais no entendimento do fluxo da água subterrânea. O presente trabalho busca aplicar o conhecimento da tectônica rúptil para caracterizar o meio fraturado, com intuito de auxiliar o estudo hidrogeológico do aqüífero. A área de estudo está localizada na porção leste do Município de Cotia, SP, no contexto do Complexo Embu, de idade proterozóica, na porção central da Faixa Ribeira. Ocorrem predominantemente rochas granitóides, com permeabilidade primária desprezível, rochas cataclásticas relacionadas às grandes zonas de cisalhamento de Taxaquara e Caucaia do Alto, metassedimentos e coberturas aluviais cenozóicas, estas ao longo das principais drenagens. Os principais eventos tectônicos de caráter rúptil da região estiveram relacionados à reativação mesozóico-cenozóica, inicialmente com a ruptura continental e abertura do Oceano Atlântico Sul e, posteriormente, a formação do Rift Continental do Sudeste do Brasil (RCSB), e seus principais eventos de deformação. Os estudos foram desenvolvidos em duas escalas de trabalho. A primeira de semi-detalhe...

Zona de cisalhamento Ribeira: deformação, metamorfismo e termobarometria de veios sin-tectônicos; Not available.

Faleiros, Frederico Meira
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 12/06/2003 Português
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17.321534%
A Zona de Cisalhamento Ribeira, de natureza transcorrente destral e direção ENE, apresenta grande importância no zonamento metamórfico e estrutural do Supergrupo Açungui, no Vale do Ribeira (SP e PR). Dados petrográficos e microestruturais indicam uma longa história deformacional da zona de cisalhamento que é caracterizada por milonitos formados em condições desde fácies anfibolito (550-600ºC) até xisto verde (300-400ºC), seguido pela geração de brechas cataclásticas, veios de quartzo tardios e pela instalação de fraturas na qual inclusões fluidas tardias foram aprisionadas em condições de 85-150ºC. Estimativas de pressão e temperatura em grupos de inclusões presentes em veios de quartzo de diferentes gerações indicam que as movimentações finais ocorreram em uma trajetória de resfriamento quase isobárico. As relações geométricas entre quatro famílias principais de zonas de cisalhamento regionais com orientações NE, ENE, NNE e NE-ENE, aliadas aos padrões de foliações e lineações de estiramento e à distribuição espacial dos elipsóides de deformação não favorecem a aplicação dos modelos transpressivos numa hipótese de geração concomitante destas estruturas. A integração dos dados existentes sobre a história deformacional suportam a hipótese de uma evolução tectônica progressiva vinculada com convergência oblíqua entre placas...

Domino structures as a local accommodation process in heterogeneous shear zones

Moreira, Noel; Dias, Rui
Fonte: Department of Earth & Environmental Sciences, KU Leuven, Belgium Publicador: Department of Earth & Environmental Sciences, KU Leuven, Belgium
Tipo: Aula
Português
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27.547146%
Usually, deformation in rocks is heterogeneously distributed, concentrating on planar zones located between rigid blocks, named shear zones. The geometry and kinematic criteria analysis becomes essential to understand the shear zones dynamics; the dominoes are one of the structures which can be used as a shear kinematic criteria. However, for the application of these structures as kinematic criteria, it is necessary a careful analysis of the tectonic environment associated with these structures. These structures are developed under ductile-brittle to brittle regimes associated to a non-coaxial deformation and obeying Coulomb criterion for failure (Jaeger & Cook, 1981). Dominoes are characterized by the clear predominance of one shear family, that induces the block rotation during the deformation process. These structures are commonly associated to extensive regimes and in strike-slip environments their development is poorly known. In such non coaxial wrench domains, these structures are frequently interpreted as asymmetric boudins at mesoscale. Current work, in Abrantes region (Central Portugal), emphasizes the presence of two major Variscan deformation phases. The second one (D2) is associated with a NW-SE right-lateral non-coaxial shear component; This deformation increase to West...

Magnetic fabric of Araguainha complex impact structure (Central Brazil): implications for deformation mechanisms and central uplift formation

Yokoyama, Elder; Trindade, Ricardo Ivan Ferreira da; Lana, Cristiano de Carvalho; Souza Filho, Carlos Roberto de; Baratoux, D.; Marangoni, Y?ra Regina; Tohver, Eric
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
Relevância na Pesquisa
28.529946%
The weakening mechanisms involved in the collapse of compleximpact craters are controversial. The Araguainhaimpact crater, in Brazil, exposes a complexstructure of 40 km in diameter, and is an excellent object to address this issue. Its core is dominated by granite. In addition to microstructural observations, magnetic studies reveal its internal fabric acquired during the collapse phase. All granite samples exhibit impact-related planar deformation features (PDFs) and planar fractures (PFs), which were overprinted by cataclasis. Cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure. Fracture planes are systematically decorated by tiny grains (< 10 ?m) of magnetite and hematite, and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) are perfectly coaxial in all studied sites. Therefore, we could track the orientation of deformation features which are decorated by iron oxides using the AMS and AAR. The magneticfabrics show a regular pattern at the borders of the central peak, with orientations consistent with the fabric of sediments at the crater's inner collar and complex in the center of the structure. Both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of compleximpactstructures. The widespread occurrence of cataclasis in the central peak...

Magnetic fabric of Araguainha complex impact structure (Central Brazil): Implications for deformation mechanisms and central uplift formation

Yokoyama, E.; Trindade, R. I. F.; Lana, C.; Souza Filho, C. R.; Baratoux, D.; Marangoni, Y. R.; Tohver, E.
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
48.856025%
The weakening mechanisms involved in the collapse of complex impact craters are controversial. The Araguainha impact crater, in Brazil, exposes a complex structure of 40 km in diameter, and is an excellent object to address this issue. Its core is dominated by granite. In addition to microstructural observations, magnetic studies reveal its internal fabric acquired during the collapse phase. All granite samples exhibit impact-related planar deformation features (PDFs) and planar fractures (PFs), which were overprinted by cataclasis. Cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure. Fracture planes are systematically decorated by tiny grains (<10 mu m) of magnetite and hematite, and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) are perfectly coaxial in all studied sites. Therefore, we could track the orientation of deformation features which are decorated by iron oxides using the AMS and AAR. The magnetic fabrics show a regular pattern at the borders of the central peak, with orientations consistent with the fabric of sediments at the crater's inner collar and complex in the center of the structure. Both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of complex impact structures. The widespread occurrence of cataclasis in the central peak...

Magnetic fabric of Araguainha complex impact structure (Central Brazil): Implications for deformation mechanisms and central uplift formation

Yokoyama, E.; Trindade, R. I. F.; Lana, C.; Souza Filho, C. R.; Baratoux, D.; Marangoni, Y. R.; Tohver, E.
Fonte: Elsevier; Amsterdam Publicador: Elsevier; Amsterdam
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
28.529946%
The weakening mechanisms involved in the collapse of complex impact craters are controversial. The Araguainha impact crater, in Brazil, exposes a complex structure of 40 km in diameter, and is an excellent object to address this issue. Its core is dominated by granite. In addition to microstructural observations, magnetic studies reveal its internal fabric acquired during the collapse phase. All granite samples exhibit impact-related planar deformation features (PDFs) and planar fractures (PFs), which were overprinted by cataclasis. Cataclastic deformation has evolved from incipient brittle fracturing to the development of discrete shear bands in the center of the structure. Fracture planes are systematically decorated by tiny grains (<10 mu m) of magnetite and hematite, and the orientation of magnetic lineation and magnetic foliation obtained by the anisotropies of magnetic susceptibility (AMS) and anhysteretic remanence (AAR) are perfectly coaxial in all studied sites. Therefore, we could track the orientation of deformation features which are decorated by iron oxides using the AMS and AAR. The magnetic fabrics show a regular pattern at the borders of the central peak, with orientations consistent with the fabric of sediments at the crater's inner collar and complex in the center of the structure. Both the cataclastic flow revealed from microstructural observations and the structural pattern of the magnetic anisotropy match the predictions from numerical models of complex impact structures. The widespread occurrence of cataclasis in the central peak...

Constitutive Law and Flow Mechanism in Diamond Deformation

Yu, Xiaohui; Raterron, Paul; Zhang, Jianzhong; Lin, Zhijun; Wang, Liping; Zhao, Yusheng
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 19/11/2012 Português
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27.665325%
Constitutive laws and crystal plasticity in diamond deformation have been the subjects of substantial interest since synthetic diamond was made in 1950's. To date, however, little is known quantitatively regarding its brittle-ductile properties and yield strength at high temperatures. Here we report, for the first time, the strain-stress constitutive relations and experimental demonstration of deformation mechanisms under confined high pressure. The deformation at room temperature is essentially brittle, cataclastic, and mostly accommodated by fracturing on {111} plane with no plastic yielding at uniaxial strains up to 15%. At elevated temperatures of 1000°C and 1200°C diamond crystals exhibit significant ductile flow with corresponding yield strength of 7.9 and 6.3 GPa, indicating that diamond starts to weaken when temperature is over 1000°C. At high temperature the plastic deformation and ductile flow is meditated by the <110>{111} dislocation glide and a very active {111} micro-twinning.

Hydrothermal alteration in an exhumed crustal fault zone: Testing geochemical mobility in the Caleta Coloso Fault, Atacama Fault System, Northern Chile

Hoshino, Kenichi; Cembrano, José; Faulkner, Daniel R.; Mitchell, Thomas M.; Fujita, Kazuna; Rempe, Marieke; Gomila, Rodrigo; Morata Céspedes, Diego Antonio; Arancibia, Gloria
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo de revista
Português
Relevância na Pesquisa
17.787314%
Artículo de publicación ISI; Crustal scale strike slip fault zones have complex and heterogeneous permeability structures, playing an important role in fluid migration in the crust. Exhumed faults provide insights into the interplay among deformation mechanisms, fluid–rock interactions and bulk chemical redistributions. We determined the whole-rock geochemistry andmineral chemistry of the fault core of the Caleta Coloso Fault inNorthern Chile, in order to constrain the physical and chemical conditions that lead to strong hydrothermal alteration. The strike-slip Caleta Coloso Fault core has a multiple-core architecture, consisting of alternate low strain rocks (protolith, weakly deformed protolith and protocataclasites) and high-strain strands (cataclasites and discrete band of ultracataclasite) derived from a Jurassic tonalite. Hydrothermal alteration associated with fault-related fluid flow is characterized by a very low-grade association consisting of chlorite, epidote, albite, quartz and calcite. Chlorite thermometry indicates T-values in the range of 284 to 352 °C, no variations in mineral composition or T-values were observed among different cataclastic units. Mass balance and volume change calculations show significantly larger chemical mobility in the protocataclasites than in the cataclasite (and ultracataclasite). This suggests that fluid flow and chemical alteration are strongly controlled by deformation being protocataclasite relatively more permeable than cataclasite. Chlorite precipitation and grain reduction in cataclasite (and ultracataclasite) would reduce permeability acting as a barrier for fluid flow. Chemical mobility and volume changes in the Coloso Fault core suggest different effective fluid/flow ratios during amalgamation of subsequent and subparallel deformation bands that finally control the fracture–channeling allowing fault-related fluid–flow into each of them.

Enhancement of fluid permeability during shear deformation of a synthetic mud

Zhang, Shuqing; Cox, Stephen
Fonte: Royal Asiatic Society Publicador: Royal Asiatic Society
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
37.547146%
This study concerns the effect of stress paths on permeability and permeability anisotropy in a synthetic mud at conditions where cataclastic flow is dominant. The synthetic mud is composed of 10 wt.% montmorillonite, 40 wt.% illite, and 50 wt.% silt-sized quartz. In the experiments where the mud was first consolidated at 90 MPa effective pressure (pe) and then also sheared at 90 MPa pe, permeability decreased continuously with increasing shear displacement; subsequent shear deformation at 30 MPa and 20 MPa effective pressure resulted in permeability increases. The permeabilities parallel to and across the mud layer are similar during shear deformation at 90 MPa pe and remain so during shear deformation at lower pe. In the experiments where shear deformation commenced at 30 MPa pe after an initial consolidation at 90 MPa, permeability increased significantly with increasing displacement. Combined effects of reducing mean effective stress and shear sliding result in permeability enhancement up to two orders of magnitude. The permeability parallel to the shear direction is one order of magnitude higher than that across the shear plane. Our shear deformation experiments at high pressures confirm the importance of stress path on the evolution of fluid permeability during shear deformation. The experimental results clearly indicate that to effectively enhance permeability and to channel fluids along shear zones in wet sediments...