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Timich, Marco, Rogério Guitarrari Azzone, Gaston Eduardo Enrich Rojas, Saulo Vieira da Silva Filho, Excelso Ruberti, and Celso De Barros Gomes. "Relações de contato entre rochas alcalinas máficas e sieníticas na Praia do Jabaquara, setor norte da Ilha de São Sebastião, SP." Geologia USP. Série Científica 19, no. 4 (December 20, 2019): 3–22. http://dx.doi.org/10.11606/issn.2316-9095.v19-157121.
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Relações de contato entre as rochas sieníticas do stock de Serraria e as rochas máficas plutônicas e hipoabissais do setor norte da suíte alcalina da Ilha de São Sebastião (Ilhabela) são descritas pela primeira vez, permitindo a indicação de relações temporais entre diferentes pulsos magmáticos. Os afloramentos apresentam variedade sienítica hololeucocrática hospedando mega-, macro- e microxenólitos de diferentes rochas, formando agmatitos. Cinco unidades principais são descritas: álcali feldspato sienitos, melassienitos, diabásios, cumulatos máficos (melagabros/clinopiroxenitos) e gabros heterogêneos. Geoquimicamente,o magmatismo alcalino bimodal encontrado na ilha é bem representado pelas rochas dos afloramentos estudados. A sequência de eventos magmáticos consiste em: colocação e cristalização de pulsos de magmas básicos alcalinos, em ambiente de câmara magmática, gerando as variedades gabroicas cumuláticas, principalmente melagabros e clinopiroxenitos com olivina, e brechas de matriz gábrica com evidências de reequilíbrio textural por ação de temperatura; intrusão de novos pulsos de magma básico alcalino, representados pelos fragmentos de diabásios, que apresentam também, reequilíbrio textural (textura granoblástica predominante); intrusão de pulso sienítico na câmara máfica que fragmentou o gabro já parcial ou totalmente cristalizado, transportando ampla proporção de xenocristais e xenólitos, o que gerou rochas classificadas como melassienitos; nova intrusão de pulso sienítico, que fragmenta todo o sistema formando um agmatito com megaxenólitos e microxenólitos de gabro cumuláticos, diabásios, agmatitos de matriz gabroica (gabros heterogêneos) e melassienitos; veios e diques de pegmatito e aplito de sienitos com quartzo cortam todos os litotipos. Todos os tipos amostrados como xenólitos apresentam algum grau de recristalização e de reação química com o magma sienítico final que os hospeda.
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Chương, Văn Đức, Trần Văn Thắng, Văn Đức Tùng, Phan Doãn Linh, and Lê Triều Việt. "Ophiolit zone of Thai Nguyen - Cao Bang." VIETNAM JOURNAL OF EARTH SCIENCES 25, no. 2 (March 19, 2018): 142–49. http://dx.doi.org/10.15625/0866-7187/25/2/11895.
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Ophiolit zone of Thai Nguyen - Cao Bang started from the border of Vietnam with China, then stretched in passing Cao Bang - Dong Khe - SacCan - to Thai Nguyen. The structure of the ophiolit zone devided into five complex :- Dunite - serpentinit - peridotite complex,- Folliation gabros complex,- Gabros - diabaz complex, ·- Bazan toleit complex,- Sediment of marginal complex.The formation of Ophiolit zone occurred in the beginingPermi and ending in the late of Triassis by overslip of Eurasian plate over Song Hien marginal sea.
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MOREIRA, César Augusto, Alice Marques PEREIRA, and Mara Lia Dias CAVALHEIRO. "Caracterização geoelétrica do gabro Santa Catarina, São Sepé (RS)." Pesquisas em Geociências 41, no. 1 (April 27, 2014): 15. http://dx.doi.org/10.22456/1807-9806.78029.
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Os métodos geofísicos são largamente empregados na pesquisa dos mais diversos tipos de depó- sitos minerais. Quando combinados com estudos diretos como geoquímica em amostras de solos ou rochas, possibilitam um aumento substancial na probabilidade de descoberta de jazimentos. Os métodos geofísicos elétricos são particularmente promissores em estudos voltados à busca de sulfetos devido ao contraste das propriedades físicas resistividade elétrica e cargabilidade. Este trabalho apresenta os resultados da aplica- ção dos métodos eletrorresistividade e polarização induzida, por meio da técnica de caminhamento elétrico, com o objetivo de avaliar o potencial mineral do gabro Santa Catarina, localizado no município de São Sepé (RS), numa região onde foram descritas várias ocorrências de ouro e sulfetos. Este gabro é classificado no domínio de Corpos Básico-Ultrabásicos Estratiformes, que reúne peridotitos, gabros e anortositos acamadados. Foram realizadas três linhas de caminhamento elétrico dispostas de forma radial, com cruzamento no centro da área e separação de 60° entre linhas e leituras de resistividade elétrica e cargabilidade em arranjo Wenner- -Schlumberger. A associação de áreas de baixa resistividade e alta cargabilidade obtida a partir de modelos de inversão bidimensionais permitiu definir zonas potencialmente mineralizadas, relacionadas com estruturas que condicionam a rede de drenagem no domínio do gabro. Pintas de ouro detectadas em campanha de prospecção geoquímica em sedimento de corrente à jusante do gabro podem ser originadas da lixiviação de depósitos contidos em fraturas, por ação de águas fluviais no domínio do gabro, possivelmente caracterizados por sulfetos e ouro associado.
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Pereira, Fabio Santos, Maria de Lourdes da Silva Rosa, and Herbet Conceição. "Condições de colocação do magmatismo máfico do Domínio Macururé, Sistema Orogênico Sergipano: Maciço Capela." Geologia USP. Série Científica 19, no. 3 (August 8, 2019): 3–29. http://dx.doi.org/10.11606/issn.2316-9095.v19-151464.
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O Maciço Capela é intrusivo nas rochas metassedimentares do Domínio Macururé, Sistema Orogênico Sergipano, no sul da Província Borborema. Ele é constituído por dioritos, hornblenditos, gabros e granitos, que hospedam enclaves tonalíticos e hornblendíticos. As formas e os contatos dos enclaves tonalíticos, aliados à presença de texturas de zoneamento inverso e oscilatório em cristais de plagioclásio e ao hábito acicular da apatita nos enclaves e dioritos sugerem coexistência de magmas máfico e félsico. Os piroxênios identificados nos gabros apresentam composições de enstatita, augita e diopsídio. Os anfibólios das rochas máficas são cálcicos e correspondem a pargasita, tschermakita e magnésio-hornblenda. A mica marrom dos hornblenditos, gabros e dioritos é rica na molécula de flogopita, enquanto a dos granitos é mais enriquecida em ferro. A granada, de ocorrência restrita aos hornblenditos e dioritos, é rica na molécula de almandina. O plagioclásio varia de albita a bytownita e o feldspato potássico é a microclina. A presença de titanita e epídoto magmáticos, coexistentes com silicatos máficos magnesianos, indica a cristalização sob condições de alta fO2, próximas ao tampão NNO. As estimativas de pressão forneceram um valor médio de 8,5 kbar, que corresponde a uma profundidade aproximada de 30 km. As temperaturas liquidus, obtidas com as composições de piroxênios e anfibólios, variam de 1.261 a 831°C. Temperaturas solidus, estimadas com o par anfibólio-plagioclásio, situam-se entre 775 e 614°C. Dados de química mineral e estimativas termobarométricas sugerem que as rochas do Maciço Capela cristalizaram-se a partir de magmas basálticos hidratados, em ambiente de arco continental.
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DAMASCENO, Fábio Bezerra, Carlos Dinges MARQUES DE SÁ, Bruno Luiz Leite MARTINS, Danilo dos Santos BARRETO, and Luan Kellvin Canuto da MOTA. "SULFETOS DO COMPLEXO GABRÓICO CANINDÉ, SISTEMA OROGÊNICO SERGIPANO." Geosciences = Geociências 39, no. 03 (September 29, 2020): 675–83. http://dx.doi.org/10.5016/geociencias.v39i03.14528.
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O Domínio Canindé, localizado na porção norte do Sistema Orogênico Sergipano, é composto por rochas metavulcânicas e metassedimentares do Complexo Canindé, sendo estas intrudidas pelo corpo gabroico denominado Complexo Gabroico Canindé. A ocorrência de mineralizações sulfetadas de Cu-Ni nos gabros já foi documentada anteriormente e será detalhada neste trabalho no que se refere à sua mineralogia e mineraloquímica, através de utilização microscopia óptica de transmissão e reflexão, de microssonda eletrônica e microscopia eletrônica de varredura. Análises por estes métodos microanalíticos permitiram identificar, em amostras coletadas nos afloramentos do Complexo Gabroico Canindé, a presença de pirita, calcopirita, pirrotita, pentlandita, esfalerita, violarita e spionkopita, com análises para os teores em elementos maiores e menores neles presentes. Entre os sulfetos identificados, a violarita (FeNi2S4) e a spionkopita (Cu39S28) ainda não haviam sido descritas anteriormente no Domínio Canindé. Evidências de alteração hidrotermal tardia nos gabros apontam para gênese dos minerais secundários violarita e spionkopita por alteração dos sulfetos primários de Ni e Cu respectivamente.
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Godoy, Antonio Misson, Otávio Augusto Ruiz Paccola Vieira, Larissa Marques Barbosa de Araújo, George Luiz Luvizotto, and Jefferson Cassu Manzano. "Ocorrência de Fe-Ti-V associado ao Magmatismo Gabro-Anortosítico da Serra da Alegria, Maciço Rio Apa, Mato Grosso do Sul." Geologia USP. Série Científica 20, no. 2 (April 16, 2020): 19–38. http://dx.doi.org/10.11606/issn.2316-9095.v20-148783.
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O Maciço Rio Apa constitui exposições de rochas paleoproterozoicas na porção extremo sul do Cráton Amazônico. A região é constituída por rochas do Complexo Rio Apa, Grupo Alto Tererê e pelo Grupo Amonguijá, formado pelas suítes Vulcânica Serra da Bocaina e Plutônica do Batólito Alumiador. O segmento norte do batólito é caracterizado por rochas ácidas-básicas da Serra da Alegria, ocorrendo, na parte central, rochas da Sequência Magmática Ácida-Intermediária, representadas pelo granito homônimo. No seu entorno, no sopé das escarpas, aflora a Sequência Magmática Gabro-Anortosítica da Serra da Alegria, composta por magnetita gabro, quartzo gabro a leuco gabro, pegmatito básico e anortosito. Essas rochas gabroides constituem uma ocorrência magmática, cumulática básica, estratiforme, semiconcordante, formada por processos de cristalização fracionada, por flotação dos plagioclásios em anortosito, nas porções superiores da câmara magmática e, na parte inferior, por segregação gravítica, a concentração de cumulus de óxido de ferro constitui magnetita gabro e magnetitito. Os minerais magmáticos identificados correspondem a andesina-labradorita, apresentando teor de anortita entre An36,76– An58,06 e clinopiroxênio cálcico do tipo ferro-augita e augita. Os óxidos de ferro predominantes são ferromagnetita, com valores de FeOt entre 88,03 e 92,98%, e titanomagnetita, com valores de TiO2 entre 1,13 e 6,39%. As fases subordinadas são representadas por vanádio magnetita, com valores de V2O5 entre 0,75 e 0,98%, e ilmenita. O magmatismo básico-anortosítico sin a pós-orogênico foi resultado da cristalização de um magma mantélico primário que, associado a processos de diferenciação, gerou variedades de gabros e diabásios de composições Fe-toleíticas e diferenciados anortosíticos, em ambientes de arco de ilha a intraplaca.
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De Jesus Rosa, Lauro Roberto, Adriane Machado, Cristine Lenz, Luciana Oliveira dos Santos, and Lucas Santana Menezes. "Análise multiespacial para mapeamento geológico: estudo de caso no corpo gabróico-granítico, Faixa de Dobramentos Sergipana / Multispacial analytics to geological mapping: case study at gabroic-granitic body, Sergipano Fold Belt." Caderno de Geografia 28, no. 53 (May 12, 2018): 337–61. http://dx.doi.org/10.5752/p.2318-2962.2018v28n53p337-361.
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Novos dados geológicos foram obtidos em um corpo gabróico-granítico na Faixa de Dobramentos Sergipana (Capela, SE), utilizando as técnicas de sensoriamento remoto e geoprocessamento integradas, em uma escala de semi-detalhe (1: 30.000). Esse corpo é constituído de um conjunto de rochas ígneas, compostas principalmente por gabros, ocorrendo ainda quartzo-dioritos e granodioritos. Nesse estudo, foram utilizados dados de magnetometria, de imagens de satélite Landsat 8 e dados TOPODATA, geoprocessados no software Quantum Gis. As informações obtidas, associadas a dados de trabalhos de campo, permitiram a identificação de novas litologias e estruturas, o que levou a uma melhor delimitação desse pluton no campo e a obtenção de um novo mapa geológico da região estudada. Com essas informações, foi possível concluir que o corpo estudado é resultado de vários pulsos magmáticos, associados a processos de mistura de magmas, que originaram uma grande variedade de rochas ígneas na área. Palavras-Chave: Sensoriamento Remoto, Geoprocessamento, Corpo Gabróico-Granítico.AbstractNew lithological data were obtained of a gabbroic-granitic body in Sergipano Fold Belt (Capela, SE), using remote sensing and geoprocessing as integrated techniques in a semi-detail scale (1:30,000). This body is composed of a number of igneous rocks, mainly gabbros, besides quartz-diorites and granodiorites. In this study, it was used magnetometry data, satellite images of Landsat 8 and TOPODATA data, geoprocessed in Quantum Gis software. With these data, coupled with information obtained in fieldworks, it was possible to identify new lithologies and structures, and as a consequence, to obtain a better field limits for this igneous pluton and a new geological map of the studied area. It is possible to conclude that these rocks are the result of many magmatic pulses, with several mixing processes, which originated a great variety of igneous rocks in the area.Keyword:. Remote sensing, Geoprocessing, Gabbroic-Granitic body.
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De Sousa, Flavio Alves. "IDENTIFICAÇÃO DAS ZONAS DE RECARGA E CARACTERIZAÇÃO DOS SISTEMAS FREÁTICOS DE IPORÁ - GO." Geoambiente On-line, no. 33 (May 25, 2019): 23. http://dx.doi.org/10.5216/revgeoamb.v0i33.52073.
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– Neste trabalho foram mapeadas as áreas de recarga do lençol freático no município de Iporá, bem como as características como litologia, tipo de solos e ocupação das terras. Foi desenvolvido através de diversas frentes, como: mapeamento e identificação das áreas de recarga através de imagem de satélite e uso de software de geoprocessamento; caracterização dos tipos de solos relacionados às zonas de recarga; medição da condutividade hidráulica dos solos nas zonas de recarga; caracterização do sistema freático e utilização de cálculos para estimativa de recarga, reserva permanente e reserva explotável. Foram identificados dois sistemas freáticos: aquífero fraturado e de dupla porosidade, sendo o de dupla porosidade desenvolvido em formações sedimentares como Furnas, Ponta Grossa e Aquidauana e o fraturado sobre rochas cristalinas como granitos e gnaisses, além de rochas alcalinas como gabros e piroxenitos. Os aquíferos apresentam reservas estimadas baixas devido ao tipo de estrutura geológica predominante no município se constituída por rochas fraturadas. Palavras-chave: Freático; explotação; recarga.
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Hernandez, Ciria C., Wenshu XiangWei, Ningning Hu, Dingding Shen, Wangzhen Shen, Andre H. Lagrange, Yujia Zhang, et al. "Altered inhibitory synapses in de novo GABRA5 and GABRA1 mutations associated with early onset epileptic encephalopathies." Brain 142, no. 7 (May 5, 2019): 1938–54. http://dx.doi.org/10.1093/brain/awz123.
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Abstract We performed next generation sequencing on 1696 patients with epilepsy and intellectual disability using a gene panel with 480 epilepsy-related genes including all GABAA receptor subunit genes (GABRs), and we identified six de novo GABR mutations, two novel GABRA5 mutations (c.880G>T, p.V294F and c.1238C>T, p.S413F), two novel GABRA1 mutations (c.778C>T, p.P260S and c.887T>C, p.L296S/c.944G>T, p.W315L) and two known GABRA1 mutations (c.335G>A, p.R112Q and c.343A>G, p.N115D) in six patients with intractable early onset epileptic encephalopathy. The α5(V294F and S413F) and α1(P260S and L296S/W315L) subunit residue substitutions were all in transmembrane domains, while the α1(R112Q and N115R) subunit residue substitutions were in the N-terminal GABA binding domain. Using multidisciplinary approaches, we compared effects of mutant GABAA receptor α5 and α1 subunits on the properties of recombinant α5β3γ2 and α1β3γ2 GABAA receptors in both neuronal and non-neuronal cells and characterized their effects on receptor clustering, biogenesis and channel function. GABAA receptors containing mutant α5 and α1 subunits all had reduced cell surface and total cell expression with altered endoplasmic reticulum processing, impaired synaptic clustering, reduced GABAA receptor function and decreased GABA binding potency. Our study identified GABRA5 as a causative gene for early onset epileptic encephalopathy and expands the mutant GABRA1 phenotypic spectrum, supporting growing evidence that defects in GABAergic neurotransmission contribute to early onset epileptic encephalopathy phenotypes.
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Rosa, Lauro Roberto de Jesus. "Uso de geotecnologias para redefinição do Corpo Gabróico-Granítico Capela, Orógeno Sergipano / Geotecnologies for the redefinition of Gabbroic-Granitic Body Capela, Sergipano Orogeny." Caderno de Geografia 29, no. 57 (April 25, 2019): 609–27. http://dx.doi.org/10.5752/p.2318-2962.2019v29n57p609-627.
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Com o advento de novas tecnologias, a geologia avançou em seu conhecimento. E técnicas de sensoriamento remoto como magnetometria, imagens de satélite Landsat 8 e dados TOPODATA, que são geoprocessados em diferentes softwares como o Quantum Gis permitiram a redefinição de novos limites geológicos na região de Capela, Sergipe. Essas informações, associadas aos dados de trabalhos de campo, permitiram a identificação de novas litologias e estruturas, o que levou a uma melhor delimitação do pluton em questão e a obtenção de um novo mapa geológico da região estudada. Este corpo abrange uma sucessão de rochas ígneas, formado por gabros, relacionados com quartzo-dioritos, comumente associados a xenólitos dos metassedimentos da rocha encaixante. Sua forma pode estar relacionada a ação de falhas rúpteis e assume-se nesse trabalho que não há dois corpos gabróico-graníticos, como antes se interpretava na região, e sim apenas um único corpo, chamado Corpo Capela. Seu formato final se deve principalmente a ação das falhas tardias que deslocam o pluton na direção NE-SW.Palavras–chave: Sensoriamento Remoto, Geoprocessamento, Corpo Gabróico-Granítico.Abstract Geological knowledge advanced with new technologies. Moreover, remote sensory like magnetometry, Landsat 8 satellite images and TOPODATA data are geoprocessing by a diversity of software like Quantum Gis that makes possible the definition of new geological limits at the area of Capela, Sergipe. The information, with work field, made identification of new lithologies and geological structures, that makes a better delimitation of a pluton in the field and a new geological map for the study area. The body has a succession of igneous rocks constituted by gabbros, associated with quartz-diorites, associated with xenoliths of metasediments from the host rock. Its shape is related to the action as rupted faults. In this paper, one can assume that it does not have two gabbroic-granitic bodies like was interpreted before in the area, but just one called Corpo Capela. Its final shape it is because the action of late faults changes the pluton in the direction NE-SW.Keywords: Remote sensing, Geoprocessing, Gabbroic-Granitic body.
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Tribuzio, R., G. Manatschal, M. R. Renna, L. Ottolini, and A. Zanetti. "Tectono-magmatic Interplay and Related Metasomatism in Gabbros of the Chenaillet Ophiolite (Western Alps)." Journal of Petrology 60, no. 12 (December 1, 2019): 2483–508. http://dx.doi.org/10.1093/petrology/egaa015.
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Abstract The Jurassic Chenaillet ophiolite in the Western Alps consists of a gabbro–mantle association exhumed to the seafloor through detachment faulting and partly covered by basaltic lavas. One of the Chenaillet gabbroic bodies includes mylonites that are transected by a network of felsic veins, thereby testifying to the interplay of ductile shearing and magma emplacement. The deformed gabbros preserve clinopyroxene porphyroclasts of primary magmatic origin, which are typically mantled by amphibole (titanian edenite) and minor secondary clinopyroxene. Titanian edenite and secondary clinopyroxene also occur as fine-grained syn-kinematic phases locally associated with fine-grained plagioclase. The felsic veins are made up of anorthite-poor plagioclase and minor titanian edenite. Geothermometric investigations document that the ductile gabbro deformation and the crystallization of the felsic veins occurred at 765 ± 50 °C and 800 ± 55 °C, respectively. With respect to undeformed counterparts, the deformed gabbros are variably enriched in SiO2 and variably depleted in Mg/(Mg + Fetot2+) and Ca/(Ca + Na). In addition, the deformed gabbros show relatively high concentrations of incompatible trace elements such as rare earth elements (REE), Y, Zr and Nb. The felsic veins are characterized by low Mg/(Mg + Fetot2+) and Ca/(Ca + Na), high SiO2 and high concentrations of incompatible trace elements. Relict clinopyroxene porphyroclasts from the deformed gabbros display a rather primitive, mid-ocean ridge-type geochemical signature, which contrasts with the trace element fingerprint of titanian edenite from both the deformed gabbros and the felsic veins. For instance, titanian edenite typically has relatively high REE abundances, with chondrite-normalized REE patterns characterized by a pronounced negative Eu anomaly. A similar trace element signature is shown by secondary clinopyroxene from the deformed gabbros. Amphibole from both the deformed gabbros and the felsic veins displays high F/Cl values. We show that the SiO2-rich hydrous melts feeding the felsic veins were involved in the high-temperature gabbro deformation and that melt–gabbro reactions led to major and trace element metasomatism of the deforming gabbros.
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Santos, Renata Barrêto, Thaíse Maria Fontes Kálix, Felisbela Maria Costa Oliveira, Evenildo Bezerra de Melo, Suely Andrade da Silva, and Márcio Luiz Siqueira Campos Barros. "CARACTERÍSTICAS PETROGRÁFICAS DE ROCHAS ESCURAS E SUA CORRESPONDÊNCIA COM ALTERABILIDADE, RESISTÊNCIAS E ÍNDICES FÍSICOS; EXEMPLO DO PRETO SÃO MARCOS." HOLOS 3 (July 3, 2014): 20. http://dx.doi.org/10.15628/holos.2014.1805.
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As rochas silicáticas escuras, como os gabros, cuja composição apresenta mais plagioclásios e minerais ferromagnesianos, sobretudo piroxênios, anfibólios e micas, mostram maior tendência à alteração, seja em meio anidro (oxidação), seja em meio aquoso, através da hidratação. Rochas escuras sofrem limitações para aplicação, seja em ambientes úmidos ou secos, graças à susceptibilidade às alterações. A grande quantidade de rejeitos poderá ser minorada através da melhor adequação da explotação (extração das pranchas e blocos) aos elementos marcadores de deformação. Assim, é necessária a análise prévia e localização da frente de produção na pedreira, de acordo com a forma e orientação do sólido segundo o qual a rocha tende a se partir naturalmente. Quanto aos índices físicos, o “Preto São Marcos” apresenta maior densidade que as rochas silicáticas claras. Os valores de porosidade e absorção d’água se mostraram compatíveis com aqueles da NBR 15844:2010, assim como as resistências mecânicas. A produção de britas a partir dos rejeitos das pedreiras contribui para redução da agressão ao meio ambiente e uso sustentado.
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Pehrsson, Sally, Simon Hanmer, and Otto van Breemen. "U–Pb geochronology of the Raglan gabbro belt, Central Metasedimentary Belt, Ontario: implications for an ensialic marginal basin in the Grenville Orogen." Canadian Journal of Earth Sciences 33, no. 5 (May 1, 1996): 691–702. http://dx.doi.org/10.1139/e96-052.
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The Raglan gabbro belt of the Ontario Grenville Orogen is coincident with the top of the Central Metasedimentary Belt boundary thrust zone, a major mid-crustal shear zone separating the Central Gneiss Belt in the footwall from the Central Metasedimentary Belt in the hanging wall. It has been suggested that the gabbros making up the belt are coeval, that they formed in a marginal basin within the Central Metasedimentary Belt, and that they formed a horizon of Theologically stiff material that controlled the localization of the top of the boundary thrust zone during its initiation as the marginal basin closed at ca. 1190 Ma. U–Pb zircon dating of plutons within the Raglan gabbro belt was undertaken to test the coeval nature of intrusions in the belt. Magmatic crystallization ages for three of the gabbros fall in the range 1246–1227 Ma, and a fourth yields a minimum age of ca. 1175 Ma. The results are permissive of a common origin for the gabbros and allow that the Raglan gabbro belt may have been related to the marginal basin, at least with respect to the later stages of its evolution. Inherited 1440–1301 Ma zircons in the gabbros suggest interaction with underlying Central Gneiss Belt crust during magmatism and support an ensialic marginal-basin model, as opposed to an island-arc model, for the evolution of the northwestern part of the Central Metasedimentary Belt.
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RAY, DWIJESH, SAUMITRA MISRA, RANADIP BANERJEE, and DOMINIQUE WEIS. "Geochemical implications of gabbro from the slow-spreading Northern Central Indian Ocean Ridge, Indian Ocean." Geological Magazine 148, no. 3 (October 12, 2010): 404–22. http://dx.doi.org/10.1017/s001675681000083x.
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AbstractGabbro samples (c. < 0.4 Ma old) dredged from close to the ‘Vityaz Megamullion’ on the slow-spreading Northern Central Indian Ridge (NCIR, 18–22 mm yr−1) include mostly olivine gabbro and Fe–Ti oxide gabbro. The cumulate olivine gabbro shows ophitic to subophitic texture with early formed plagioclase crystals in mutual contact with each other, and a narrow range of compositions of olivine (Fo80–81), clinopyroxene (magnesium number: 85–87) and plagioclase (An67–70). This olivine gabbro could be geochemically cogenetic with the evolved oxide gabbro. These gabbro samples are geochemically distinct from the CIR gabbro occurring along the Vema, Argo and Marie Celeste transform faults and can further be discriminated from the associated NCIR basalts by their clinopyroxene (augite in gabbro, and diopsidic in basalts) and olivine (gabbro: Fo80–81, basalts: Fo82–88) compositions. Our major oxide, trace element and REE geochemistry analyses suggest that the gabbro and the NCIR basalts are also not cogenetic and had experienced different trends of geochemical evolution. The clinopyroxenes of the present NCIR gabbros are geochemically similar to primitive melt that is in equilibrium with mantle peridotite, and do not show any poikilitic texture with resorbed plagioclase; these results negate the possibility of these gabbros being a pre-existing cumulate that has been brought up to the shallower oceanic crust and interacted with the NCIR basalt. The Sr, Pb and Nd isotopic data of the gabbro substantially differ from those of the NCIR basalts and suggest significant contamination of the depleted mantle source of the gabbro, most likely by the Indian Ocean pelagic sediments. The Pb-isotope data suggest that the proportion of pelagic sediment that mixed in the depleted mantle source of the NCIR gabbro is much higher than the level of contamination observed for the Indian Ocean MORBs.
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Nguyen, Du, Tomoaki Morishita, Yusuke Soda, Akihiro Tamura, Biswajit Ghosh, Yumiko Harigane, Lydéric France, et al. "Occurrence of Felsic Rocks in Oceanic Gabbros from IODP Hole U1473A: Implications for Evolved Melt Migration in the Lower Oceanic Crust." Minerals 8, no. 12 (December 10, 2018): 583. http://dx.doi.org/10.3390/min8120583.
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Felsic rocks are minor in abundance but occur ubiquitously in International Ocean Discovery Program Hole U1473A, Southwest Indian Ridge. The trace element abundances of high-Ti brown amphibole, plagioclase, and zircon in veins, as well as the presence of myrmekitic texture in the studied felsic rocks support crystallization origin from highly-evolved melts, probably controlled by fractional crystallization. Based on geochemical criteria and texture of the mineral assemblage in felsic rocks and their relationship with host gabbros, they can be divided into three types: (1) Felsic rock with sharp boundaries is formed when felsic melt intrudes into fractures of host gabbros, resulting in minimal interaction between the melt and the wall minerals. (2) Replacive felsic rock, which is characterized by a pseudomorphic replacement of minerals in the host gabbro. This vein type is caused by the replacement of the host mineralogy by minerals in equilibrium with the felsic melts. (3) Felsic rock with diffused boundaries is formed either by infiltration of felsic melt into the solidifying gabbro body or crystallization of interstitial melts. Infiltration modes of felsic melts are likely controlled by the temperature condition of the cooling host gabbros.
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LI, ZHEN, JIAN-SHENG QIU, and XI-SHENG XU. "Geochronological, geochemical and Sr–Nd–Hf isotopic constraints on petrogenesis of Late Mesozoic gabbro–granite complexes on the southeast coast of Fujian, South China: insights into a depleted mantle source region and crust–mantle interactions." Geological Magazine 149, no. 3 (September 16, 2011): 459–82. http://dx.doi.org/10.1017/s0016756811000793.
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AbstractThe Quanzhou (QZ) and Huacuo (HC) gabbro–granite complexes on the southeast coast of Fujian, South China, are important components of a Late Mesozoic calc-alkaline volcanic–plutonic belt in the region. The complexes provide an excellent opportunity to investigate the genetic relationships between acid and basic magmas, and their interactions within the intrusive environment. The complexes are composed mainly of monzogranite and biotite granodiorite in the QZ complex, and biotite granite in the HC complex, with lesser amounts of hornblende gabbro. Zircon U–Pb dating provides consistent crystallization ages of 109 ± 1 Ma and 108 ± 1 Ma for the QZ gabbros and monzogranites, and an age of 111 ± 1 Ma for the HC gabbro, which is contemporaneous with the spatially associated HC granites. Both the mafic and felsic intrusions in these complexes are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs), and are depleted in high-field-strength elements (HFSEs; e.g. Nb and Ta). They show similarly homogeneous Sr–Nd isotopic compositions. All these factors indicate a close genetic relationship between the gabbroic and granitic rocks in the QZ and HC complexes. Although the enriched Sr–Nd isotopic signatures of the QZ and HC gabbros seemingly point to an enriched mantle source (EM-1), they have highly variable zircon Hf isotopic compositions, with εHf(t) values ranging from negative to positive (specifically –4.6 to +6.1 for the QZ gabbros and –4.8 to +11.6 for the HC gabbros). We interpret the parental basic magmas of these gabbros to have received contributions from a depleted mantle source and crustal components. Contributions from such a depleted mantle source resulted in the growth of juvenile basaltic lower crust, the partial melting of which generated the parental felsic magmas of the QZ and HC complexes. Furthermore, based on a synthesis of petrography, geochronology, elemental and isotopic geochemistry and tectonics, we propose that break-off and rollback of the Late Mesozoic subducted Palaeo-Pacific Plate triggered the upwelling of asthenospheric mantle below the coastal area of the South China Block, which induced extension of the overlying continental lithosphere, and finally initiated the large-scale Late Yanshanian magmatism in the study area.
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BERNSTEIN, STEFAN, and DENNIS K. BIRD. "Formation of wehrlites through dehydration of metabasalt xenoliths in layered gabbros of the Noe-Nygaard Intrusion, Southeast Greenland." Geological Magazine 137, no. 2 (March 2000): 109–28. http://dx.doi.org/10.1017/s0016756800003794.
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The Noe-Nygaard Intrusion is a 4 × 2.5 km stock composed of layered gabbros and wehrlites within the Precambrian basement of the coastal mountains west of the Kialineq Plutonic Complex. Transgressive relationships to Tertiary mafic dykes and the occurrence of abundant metabasaltic xenoliths signify a Tertiary age for the intrusion. The intrusion is characterized by alternating zones of gabbro and wehrlite; gabbro is both intruded and replaced by wehrlite, and the wehrlite zones are characterized by abundant metabasaltic xenoliths. Based on 87Sr/86Sr ratios, mica, olivine and oxide gabbros are all cumulates, crystallized at different differentiation stages from a common parental magma. Field relations, together with similarities in strontium isotope ratios, and in the major and rare earth element (REE) mineral chemistry between gabbros and wehrlites, indicate that the wehrlite bodies were formed by the dissolution of plagioclase from a gabbro cumulate mush by H2O derived from dehydration and the partial assimilation of metabasaltic xenoliths. In terms of their REE characteristics, melts from which the Noe-Nygaard Intrusion crystallized are within the compositional range of melts for other early Tertiary mafic/ultramafic complexes of East Greenland. However, they were generated at a greater mean melting pressure, and have less radiogenic strontium isotope ratios than the nearby Imilik mafic/ultramafic complex, supporting existing models for mantle heterogeneity at the time of continental break-up. The abundance of metabasaltic xenoliths in the Noe-Nygaard Intrusion provides further evidence for the lateral extent of the North Atlantic flood basalt province, which onshore has been mostly removed by glacial erosion south of 68° N in Greenland.
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Akamatsu, Yuya, Kumpei Nagase, and Ikuo Katayama. "Non-Dilatant Brittle Deformation and Strength Reduction of Olivine Gabbro due to Hydration." Minerals 11, no. 7 (June 28, 2021): 694. http://dx.doi.org/10.3390/min11070694.
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To investigate the influence of hydration on brittle deformation of oceanic crustal rocks, we conducted triaxial deformation experiments on gabbroic rocks with various degrees of hydration at a confining pressure of 20 MPa and room temperature, measuring elastic wave velocity. Hydrated olivine gabbros reached a maximum differential stress of 225–350 MPa, which was considerably less than those recorded for gabbros (~450 MPa), but comparable to those for serpentinized ultramafic rocks (250–300 MPa). Elastic wave velocities of hydrated olivine gabbros did not show a marked decrease even prior to failure. This indicated that the deformation of hydrated olivine gabbro is not associated with the opening of the stress-induced cracks that are responsible for dilatancy. Microstructural observations of the samples recovered after deformation showed crack damage to be highly localized to fault zones with no trace of stress-induced crack opening, consistent with the absence of dilatancy. These data suggest that strain localization of hydrated olivine gabbro can be caused by the development of shear cracks in hydrous minerals such as serpentine and chlorite, even when they are present in only small amounts. Our results suggest that the brittle behavior of the oceanic crust may considerably change due to limited hydration.
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Paschoalin Filho, João Alexandre, Diego Gonçalves Camelo, David de Carvalho, António José Guerner Dias, and Brenno Augusto Marcondes Versolatto. "Use of construction and demolition solid wastes for basket gabion filling." Waste Management & Research: The Journal for a Sustainable Circular Economy 38, no. 12 (May 15, 2020): 1321–30. http://dx.doi.org/10.1177/0734242x20922591.
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Construction and demolition wastes have been studied by technical means aiming at the development of management tools to reduce their environmental impacts. Among these, recycling can be highlighted. This paper aims at the technical assessment of basket gabions filled with construction and demolition solid waste. Gabions are usually used for retaining walls construction, and these are commonly filled with rocks. Retaining walls are essential for earthfill slopes stabilization, and they must have proper characteristics of strength. However, depending on the slope height or the technical responsibility of the retaining wall, alternative materials with proper characteristics could be used to fill the gabions. The use of recycled material for gabion filling could reduce environmental impacts and costs caused by retaining wall construction. So, basket gabion cells were filled with construction solid waste and basaltic rocks, both crushed into coarse granulometry aiming to compare technical characteristics among them. The performed laboratory tests showed that the horizontal and vertical displacements determined for gabion filled with wastes were near to those obtained for gabions filled with basaltic rocks for a retaining wall of 5 m and up. In conclusion, it can be drawn that basket gabions filled with construction and demolition waste may be a technical alternative for civil construction, reducing environmental impacts and raw material consumption for retaining wall execution.
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JAFARI, MORTEZA KHALATBARI, HASSAN A. BABAIE, and MOJTABA MIRZAIE. "Geology, petrology and tectonomagmatic evolution of the plutonic crustal rocks of the Sabzevar ophiolite, NE Iran." Geological Magazine 150, no. 5 (March 21, 2013): 862–84. http://dx.doi.org/10.1017/s0016756812000933.
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AbstractThe plutonic crustal sequence exposed northeast of Sabzevar is part of the ophiolitic belt of Sabzevar that occurs along the northern margin of the Central Iran micro-continent. The sequence includes olivine and pyroxene gabbro with cumulate characteristics, isotropic gabbro, foliated gabbro and a diabase sheeted dyke complex cut by wehrlite and olivine websterite intrusions, and pegmatite gabbro and plagiogranite as small intrusions and dykes. The sequence is comparable to gabbros in known ophiolite complexes. Microscopic studies show an abundance of the mesocumulate and heteradcumulate textures that represent open system magma chambers, which are common in supra-subduction zones. The olivine → plagioclase → clinopyroxene → ± orthopyroxene → amphibole trend of mineralization in the gabbros, similar to mid-ocean ridge basalt (MORB), and olivine → clinopyroxene → ± orthopyroxene → plagioclase → amphibole, similar to arc rocks, indicate the diversity in the formation of these rocks, and represent petrographic evidence of their formation in a supra-subduction zone. The rocks have calc-alkaline to tholeiitic affinities, and niobium depletion in the spider diagrams of diabase that matches the patterns of island arc magma. These patterns, and the light rare earth element enrichment of the diabase and plagiogranite, suggest the effect and introduction of the fluids, originating from the subducting slab, beneath the mantle wedge. The low titanium compositions, matching those of arc diabase and plagiogranite, plot in the island arc to MORB tectonomagmatic fields, and suggest formation of the Sabzevar ophiolitic plutonic crustal sequence in a supra-subduction zone during Late Cretaceous time.
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Bernstein, Stefan, Minik T. Rosing, C. Kent Brooks, and Dennis K. Bird. "An ocean-ridge type magma chamber at a passive volcanic, continental margin: the Kap Edvard Holm layered gabbro complex, East Greenland." Geological Magazine 129, no. 4 (July 1992): 437–56. http://dx.doi.org/10.1017/s001675680001952x.
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AbstractThe gabbros of the Tertiary Kap Edvard Holm Layered Serieshave a stratigraphic thickness of more than 5000 m. Earlier work has shown that the range in cumulus mineral compositions is restricted (plagioclase An81—An51; olivine Fo85—Fo66; pyroxenes Ca43Mg46Fe11 to Ca43Mg37Fe20). Field evidence of magma injections is common, which together with the restricted range in mineral chemistry suggests that the magma chamber was frequently replenished by a less fractionated magma. A detailed study of a 600 m section (900–1500 m) in the Lower Layered Series reveals a period of crystallization when the magma chamber behaved as a closed system (900–1300 m). The rocks formed during this periodare well-laminated olivine–gabbros (900–110 m), which evolved to well-laminated oxide-gabbros (1100–1300 m). Compositional trends in the cumulusminerals are towards more evolved compositions (plagioclase An64—An58, pyroxene Mg# from 80 to 76) with stratigraphic height. From 1300 m to 1500 m, granular olivine-gabbros dominate, with moreprimitive mineral compositions (plagioclase An67—An76, pyroxene Mg# from 78 to 82). The transition olivine–gabbro to oxide-gabbro at 1100m is a consequence of fractional crystallization, and it is shown how changes in activities of FeO and Fe203 in the magma are reflected in the total iron content of plagioclases.The transition from oxide-gabbro to olivine-gabbro at 1300 m results from replenishment by less evolved basaltic magma. On the basis of calcic pyroxene chemistry and the mineral crystallization sequence it is concluded that the Kap Edvard Holm Layered Series crystallized from a tholeiitic magma similar to MORB. Melanogabbroic units occur throughout the intrusion as discordant to subconcordant sill-like bodies 0.2–2.0 m thick. The melanogabbroic units consist of Cr-rich augite-olivine-plagioclase heteradcumulates and contain deformed mica crystals of pre-emplacement origin. These units crystallized from a wet, MgO-rich magma which was injected into the layered host gabbros after the formation of the cumulus pile, but before the magma was completely solidified.The Kap Edvard Holm Layered Series has several parallels with the plutonic part of ophiolite sequences. These include: cumulus mineral assemblage, compositions of the minerals and the restricted range in compositions with stratigraphic height; field evidence of repeated replenishment of basaltic magma; dyke swarms overlying the roof zone of the magma chamber; and the existence of a late intrusive suite of wet, MgO-rich magma. These parallels suggest that the processes involved in the formation of the Kap Edvard Holm Layered Series were similar to those involved in the formation of the crustalpart of many ophiolites and beneath present-day spreading ridges. The Kap Edvard Holm Layered Series is therefore believed to represent a shallow-level magma chamber which acted as a reservoir for basaltic flows at the continental margin during the opening of the North Atlantic Ocean.
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Bevins, R. E., G. J. Lees, R. A. Roach, G. Rowbotham, and P. A. Floyd. "Petrogenesis of the St David's Head Layered Intrusion, Wales: a complex history of multiple magma injection and in situ crystallisation." Transactions of the Royal Society of Edinburgh: Earth Sciences 85, no. 2 (1994): 91–121. http://dx.doi.org/10.1017/s0263593300003515.
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AbstractThe St David's Head Intrusion, exposed in North Pembrokeshire, is a tholeiitic sill up to 570 m thick, comprising principally mafic gabbros, which are in part layered. Layering varies from the centimetre to the metre scale. A range of gabbroic compositions is present, defining seven major petrological types, which are cut by thin silicic (aplitic) veins.Log–log plots of incompatible elements from the various lithological units indicate that all of the rocks in the intrusion are petrogenetically linked, although a variety of processes has been operative. Roach (1969) considered the quartz gabbros and dolerites, which form an envelope around the other units, to relate most closely to the parental composition. However, the least evolved compositions in the intrusion are from the xenolithic laminated olivine gabbros, although these mafic compositions are due primarily to the presence of abundant, mafic, cognate xenoliths. These xenoliths are thought to relate to an earlier episode of crystal accumulation in a high-level magma chamber. The various laminated gabbros reflect crystal accumulation in situ after magma emplacement, leading in certain layers to extreme enrichments in Fe, Ti, and V, related to high modal proportions of cumulus ilmenite. Further in situ crystallisation led to differentiation of the residual liquid, producing more silicic gabbros with well-developed granophyric textures, the granophyre reflecting the silicic residuum. Extreme differentiation, possibly combined with expulsion of silicic residual liquid during crystal accumulation and compaction, resulted in the cross-cutting aplite veins.Three different types of layering are present in the intrusion. Firstly, preferred orientation of tabular minerals in the laminated gabbro units is thought to result from discrete sedimentation episodes from a convecting magma chamber. Secondly, macrorhythmic modal layering up to 1 m thick consists of an alternation of relatively ilmenite-rich and ilmenite-poor layers in the laminated gabbro units, although the reason for the modal variation is not certain. Thirdly, a centimetre-scale felsic–mafic microrhythmic layering is present in the envelope quartz gabbros and dolerites, which is similar to the inch-scale layering in the Stillwater Igneous Complex. This layering is thought to relate to metasomatic reaction in the gabbro in the presence of water at a late magmatic stage. Overall, these various lithological units themselves define a large-scale layering in the intrusion.Combined, the petrological and geochemical data suggest that the St David's Head Intrusion was not emplaced in a single event. Rather, a series of magma pulses, of contrasting compositions but petrogenetically linked, was intruded. Some of the chemical variations now seen existed prior to emplacement, indicating the former presence of high-level crustal magma chambers, while other variations developed as a result of in situ crystallisation processes and related chemical differentiation.
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Lamerdonov, Z. G., T. Yu Khashirova, S. A. Zhaboev, M. A. Enaldieva, A. M. Chochieva, and K. Z. Lamerdonov. "Operational Experience of Gabion Shore Protection Structures on Mountain Rivers and Some Suggestions for their Improvement." Ecology and Industry of Russia 24, no. 10 (October 14, 2020): 8–12. http://dx.doi.org/10.18412/1816-0395-2020-10-8-12.
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The paper presents the accumulated experience in the construction and operation of gabions. The results of field surveys of gabions, their advantages and disadvantages, which must be taken into account in environmental practice, are presented. Innovative developments of sloping fasteners made of semi-cylindrical gabions and their construction technologies are presented. Variants of flexible retaining walls of semi-cylindrical gabions are proposed, with lower specific pressures on the soil of the base and enhanced bearing capacity on the action of bending moments. Experimental studies of prismatic and cylindrical gabion models have been carried out for a comparative assessment of their work.
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Clarke, Sam, Andrew Barr, Jim Warren, and Angus Williams. "Local variations in gabion structures." International Journal of Protective Structures 9, no. 4 (April 12, 2018): 415–31. http://dx.doi.org/10.1177/2041419618766153.
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Gabion structures are widely used for force protection as they enable locally available material to be used, reducing logistical expense. The soil fill within these structures provides the blast and ballistic resistance; hence, any localised variation in the contained soil can potentially lead to reductions in protective capability. Specifically, built gabion structures were monitored in internal and external environments to assess the variation of soil moisture content and density over a full year and with changing weather conditions. The gabions were filled with fine sand according to manufacturer’s instructions. Internal and external moisture content readings were recorded at regular intervals, and a continuously monitoring weather station was installed to collect comparative data. LIDAR scanning was used to record the shape and volume of the gabions to estimate variations in the density of the soil fill. The data indicate that moisture content can vary by over 20% between the top and base of the gabion, and by over 5% from face to face and between readings depending on recent weather conditions, while the core of the gabions remains relatively unaffected. This leads to localised variations in density which can impact on both the ballistic performance and blast resistance of the structure.
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Adilov, Farkhadjan, and Rustam Abirov. "On numerical investigation of stability of roadbeds reinforced by gabion structures." E3S Web of Conferences 264 (2021): 02004. http://dx.doi.org/10.1051/e3sconf/202126402004.
Full textAbstract:
The stability of roadbed in seismic prone areas is vital for the sustainable economic development of regions. The gabion structures are one of the methods of road strengthening. Gabion structures are used to avoid damage to the roadbed under loads of natural ground slope due to earthquake or other reasons. This approach is one of the most economical and efficient solutions for the stabilization of natural ground slopes, and it is efficient as a drainage system. Field tests give precise results about the efficiency of gabion types for different sites. However, in some cases, it is expensive and numerical calculation can be used for the estimation of the applicability of gabions. The stability of roadbed by using finite element approaches was investigated here. Stability was considered as results of calculations by two cases with gabions and without ones were compared. The dynamic and seismic impact was taken into account according to local normative documents.
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Taher, Ratna, Makruf Nurudin, and Eko Hanudin. "Characteristics of Soils Developing from Gabbro, Phyllite and Chert Parent Rock in Karangsambung District." Ilmu Pertanian (Agricultural Science) 4, no. 3 (November 29, 2019): 131. http://dx.doi.org/10.22146/ipas.32392.
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Understanding the nature of the soil is very important to know the potential and the proper management of the soil. This study aimed to determine the differences in morphological, physical, and chemical properties of the soils developing from gabbro, phylitte and chert parent materials. The soil profile was made to represent each parent rock of gabbro, phyllite and chert located on the upper and middle slopes with pine-dominated vegetation and mixed gardens. Observation in the field is a professional description to observe soil morphology. Soil samples were taken at each horizon to analyze soil physical properties (bulk density, particle density, and texture), soil chemical properties (pH, exchanged cations, cation exchange capacity, available P, organic C, and total N). Texture analysis results showed that clay content of the soil developing from parent rock of Gabro 1 is the highest, followed by the soil clay content from Chert 1, Phyllite 1, Chert 2, Phyllite 2, and Gabbro 2, respectively. The order of soil acidity level (pH) is Gabbro 2 > Gabbro 1> Chert 1 ~ Chert 2 > Phyllite 1 ~ Phyllite 2. Meanwhile, the order of the cation exchange capacity is Gabbro 1> Gabbro 2> Phyllite 1> Chert 1> Phyllite 2> Chert 2, and the order of the base saturation is Chert 2> Gabbro 2> Chert 1> Phyllite 2 > Phyllite1> Gabbro 1.
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Glykys, Joseph, and Istvan Mody. "Hippocampal Network Hyperactivity After Selective Reduction of Tonic Inhibition in GABAA Receptor α5 Subunit–Deficient Mice." Journal of Neurophysiology 95, no. 5 (May 2006): 2796–807. http://dx.doi.org/10.1152/jn.01122.2005.
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Functionally, γ-aminobutyric acid receptor (GABAR)–mediated inhibition can be classified as phasic (synaptic) and tonic (extrasynaptic). The GABARs underlying tonic inhibition assemble from subunits different from those responsible for phasic inhibition. We wanted to assess the excitability of hippocampal pyramidal cell (PC) networks following a selective impairment of tonic inhibition. This is difficult to accomplish by pharmacological means. Because the GABAR α5 subunits mostly mediate the tonic inhibition in CA1 and CA3 PCs, we quantified changes in tonic inhibition and examined network excitability in slices of adult gabra5−/− mice. In gabra5−/− CA1 and CA3 PCs tonic inhibitory currents were 60 and 53%, respectively, of those recorded in wild type (WT), with no alterations in phasic inhibition. The amount of tonic inhibition recorded in slices was significantly affected by the method of slice storage (interface or submerged chamber). Field recordings in gabra5−/− CA3 pyramidal layer showed an increased network excitability that was decreased by the GABAR agonist muscimol at a concentration that restored the tonic inhibition of gabra5−/− PCs to the WT level without altering phasic inhibition. Through a battery of pharmacological experiments, we have identified δ subunit–containing GABARs as the mediators of the residual tonic inhibition in gabra5−/− PCs. Our study is consistent with an important role of tonic inhibition in the control of hippocampal network excitability and highlights selective enhancers of tonic inhibition as promising therapeutic approaches for diseases involving network hyperexcitability.
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Lindsay, Jordan J., Hannah S. R. Hughes, Dermot Smyth, Iain McDonald, Adrian J. Boyce, and Jens C. Ø. Andersen. "Distinct sulfur saturation histories within the Palaeogene Magilligan Sill, Northern Ireland: implications for Ni – Cu – platinum group element mineralisation in the North Atlantic Igneous Province." Canadian Journal of Earth Sciences 56, no. 7 (July 2019): 774–89. http://dx.doi.org/10.1139/cjes-2018-0141.
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The ∼60 m thick Magilligan Sill is part of the British Palaeogene Igneous Province in the North Atlantic. The sill comprises layers of dolerite and olivine gabbro, and it intrudes a thick sequence of Mesozoic mudstones and marls, which are locally baked at the sill margins. Since 2014, the sill has been an exploration target for orthomagmatic Ni – Cu – platinum group element (PGE) sulfide mineralisation analogous to the Noril’sk-Talnakh intrusion in Russia. We present new petrological, geochemical, and S isotope data to assess the prospectivity of the sill and the underlying magmatic plumbing system. Most sulfides in the dolerite portions of the sill are <50 μm in size and comprise only pyrite with PGE abundances below the detection limit. In the olivine gabbros, >150 μm size pentlandite, chalcopyrite, and pyrrhotite grains contain <4 ppm total PGE, 1460 ppm Co, and 88 ppm Ag. Pyrite from the dolerites have δ34S ranging from −10.0‰ to +3.4‰ and olivine gabbro sulfides range from −2.5‰ to −1.1‰, suggesting widespread crustal contamination. The S/Se ratios of sulfides in the dolerites and olivine gabbros range from 3500 to 19 500 and from 1970 to 3710, respectively, indicating that the latter may have come from upstream in the magma plumbing system. The Magilligan Sill records multiple injections of mafic magma into an inflating sill package, each with distinct mechanisms towards S saturation. Whilst the sulfide minerals in the sill do not constitute significant mineralisation themselves, detailed in situ studies highlight a divergence in S saturation histories and suggest that a larger volume of olivine gabbro sulfides at depth may be prospective.
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Pe-Piper, Georgia, David J. W. Piper, and Basilios Tsikouras. "The late Neoproterozoic Frog Lake hornblende gabbro pluton, Avalon Terrane of Nova Scotia: evidence for the origins of appinites." Canadian Journal of Earth Sciences 47, no. 2 (February 2010): 103–20. http://dx.doi.org/10.1139/e09-077.
Full textAbstract:
The late Neoproterozoic Frog Lake pluton, in the Avalon terrane of the Cobequid Highlands, Nova Scotia, consists predominantly of hornblende gabbro. It shows petrographic similarities to water-rich mafic intrusions known as appinites that are present in some collisional orogens. This study aims to further understanding of the origin of appinitic intrusions. In the field, the main hornblende gabbro was intruded between screens of metasedimentary country rock that is of upper greenschist metamorphic grade. The contacts appear to have been pathways for magma of gabbroic, tonalitic–granodioritic, and granitic composition that carried enclaves of gabbroic lithologies. Some of these magmas had a high volatile content, resulting in abundance of hydrous mineral phases, pegmatites, and diffuse felsic segregations. These varied rocks in the contact zones experienced progressive shear resulting in syn-magmatic deformation. Low-Ti hornblende gabbros have trace-element abundances similar to subduction-related low-K mafic rocks, including some enrichment in large-ion lithophile elements and marked relative depletion in Nb and Y. High-Ti hornblende gabbros and pyroxene–mica gabbro show more alkaline characteristics, with higher amounts of Nb, Y, P2O5, and high-field-strength elements. Tonalite and granite veins are geochemically similar to volcanic-arc granite. Comparison with appinites in the literature suggests that the Frog Lake pluton represents a deeper structural level than most appinites. The Frog Lake appinites were part of the feeder system to back-arc volcanic rocks of the Jeffers Group. Comparison with other appinites also leads to the conclusion that there is not a single type of “appinitic magma”: different appinitic plutons range in composition from low-K calc-alkaline to shoshonitic. The essential characteristic is a water-rich mafic magma. Appinites occur in settings undergoing crustal-scale strike-slip shear, where the faults allow rapid rise of mafic magma to shallow crustal levels.
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Klassen, H. D., and T. G. Northcote. "Stream bed configuration and stability following gabion weir placement to enhance salmonid production in a logged watershed subject to debris torrents." Canadian Journal of Forest Research 16, no. 2 (April 1, 1986): 197–203. http://dx.doi.org/10.1139/x86-036.
Full textAbstract:
Tandem V-shaped gabion weirs for improving spawning habitat for salmon (Oncorhynchus spp.) were installed to replace large organic debris at three sites below the terminus of a debris torrent in Sachs Creek, Queen Charlotte Islands. Stream conditions were compared between gabion and nearby control sites. The stability of added and entrapped gravel at all gabion sites was poor over the first winter and excessive scour threatened the integrity of the upstream steeper (3%) slope gabion site. However, the two gabion sites at a lower (1%) slope successfully stabilized spawning gravel in the 2nd year after installation, probably through a reduction in the local slope gradient and self-armouring of the high flow channels. Higher summer densities of juvenile coho salmon (Oncorhynchuskisutch (Walbaum)) and steelhead trout (Salmogairdneri Richardson) were recorded at the gabion sites (means, 1.2 and 0.33/m2, respectively) compared with the control sites (means, 0.89 and 0.10/m2). Underyearling coho fry were also significantly larger (p < 0.05) at gabion sites (mean, 50 mm) than at control sites (mean, 45 mm). Improved rearing habitat was created for coho juveniles by the gabions, a result of increased pool area and cover.
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Hassanipak, A. A., A. Mohamad Ghazi, and J. M. Wampler. "Rare earth element characteristics and K–Ar ages of the Band Ziarat ophiolite complex, southeastern Iran." Canadian Journal of Earth Sciences 33, no. 11 (November 1, 1996): 1534–42. http://dx.doi.org/10.1139/e96-116.
Full textAbstract:
The Band Ziarat complex of southeastern Iran is located on the western boundary of the Jaz Murian depression and is bounded by two major fault systems. The principal rock units of this complex are a gabbro sequence that includes low-and high-level cumulate gabbros, a late intrusive sequence that consists of diorite and plagiogranite, and a volcanic sequence that includes diabase dikes and a lesser amount of basaltic lava. Mantle rocks are virtually absent because of the presence of the two bounding fault systems, but we consider the complex to be an ophiolite in nature. Rare earth element (REE) whole-rock data clearly differentiate the classic ophiolitic lithologies for the crustal rocks in this complex. Based on the REE data, there are two distinct types of basalt present at Band Ziarat: (i) those that formed from an initial basaltic melt with a light rare earth element (LREE) enriched signature (similar to intraplate basalts), and (ii) those that have LREE-depleted patterns (similar to normal mid-ocean-ridge basalts). The data also suggest (i) that the gabbros are accumulates and were derived from a source slightly enriched in LREE, with fractionation controlled by removal of clinopyroxene or hornblende and plagioclase, and (ii) that the late intrusive rocks as well as a majority of the diabase dikes are cogenetic and were derived from the same LREE-enriched source. K–Ar ages ranging from 134 ± 4 to 146 ± 5 Ma for low-level gabbros and from 121 ± 4 to 130 ± 4 Ma for high-level gabbros were measured on five hornblende and two whole-rock samples, which suggests that these rocks may have formed early in the Cretaceous period.
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Pimentel, Márcio M., Maria Helena B. M. Hollanda, and Richard Armstrong. "Shrimp U-Pb age and Sr-Nd isotopes of the Morro do Baú mafic intrusion: implications for the evolution of the Arenópolis volcano-sedimentary sequence, Goiás Magmatic Arc." Anais da Academia Brasileira de Ciências 75, no. 3 (September 2003): 331–39. http://dx.doi.org/10.1590/s0001-37652003000300006.
Full textAbstract:
The Arenópolis volcano-sedimentary sequence is located in the southern part of the Goiás Magmatic Arc and includes a ca. 900 Ma calc-alkaline arc sequence made of volcanic rocks ranging in composition from basalts to rhyolites, metamorphosed under greenschist to amphibolite facies. Small calc-alkaline gabbro to granite sub-volcanic bodies are also recognized. The Morro do Baú intrusion is the largest of these intrusions, and is made of gabbros and diorites. Zircon grains separated from one gabbro sample and analyzed by SHRIMP I yielded the mean 206Pb/238U age of 890 +/- 8 Ma, indicating that the intrusion is roughly coeval or only slightly younger than the Arenópolis volcanics. Contrary to the metavolcanics, which are juvenile, the Nd isotopic composition of the Morro do Baú gabbro indicates strong contamination with archean sialic material (T DM of 2.8 Ga and EpsilonNd(T) of -9.7), represented in the area by an allochthonous sliver of archean/paleoproterozoic gneisses (Ribeirão gneiss) which are the country-rocks for the gabbro/dioritic intrusion. The emplacement age of ca. 890 Ma represents a minimum age limit for the tectonic accretion of the gneiss sliver to the younger rocks of the Arenópolis sequence. The data suggest that this happened early in the evolution of the Goiás Magmatic Arc, between ca. 920 and 890 Ma.
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Tegner, Christian, and J. Richard Wilson. "A late ultramafic suite in the Kap Edvard Holm layered gabbro complex, East Greenland." Geological Magazine 130, no. 4 (July 1993): 431–42. http://dx.doi.org/10.1017/s0016756800020513.
Full textAbstract:
AbstractThe Kap Edvard Holm Complex is an early Tertiary layered gabbro situated on the western side of the Kangerdlugssuaq fjord. Layered olivine gabbros in the Taco Point area are cut by several wehrlitic sill-like bodies which comprise a late ultramafic suite. An intrusive wehrlitic facies in the inner part of the bodies consists of olivine (+minor chrome-spinel) orthocumulate with clinopyroxene oikocrysts and interstitial plagioclase, kaersutite and phlogopite. A replacive facies which occurs in the marginal zones is texturally similar to the intrusive facies but contains no chromespinel and is more feldspathic, varying from a melanocratic olivine gabbro to a feldspathic wehrlite. It occurs where the sills wedge out laterally, in the lower contact zones where finger structures are widely developed, and in the upper contact zones where wehrlitic pipes feed melanocratic sheets, called parasol structures, which preferentially follow mafic layers in the host olivine gabbro. The wehrlites formed by the intrusion of hot, hydrous, ultrabasic magma into consolidated layered olivine gabbro. The replacive facies was formed by the volume for volume metasomatic replacement of olivine gabbro; dissolution of plagioclase was accompanied by crystallization of olivine. Some clinopyroxene was initially resorbed and later reprecipitated during this process. The relatively dense pore magma migrating upwards was restricted to pipes and spread out laterally when it encountered readily replaced mafic layers, while below the sills gabbro was replaced en masse and finger structures were formed. Similar late ultramafic suites occur in ophiolites, and their presence in the Kap Edvard Holm Complex supports suggestions that it acted as an ocean ridge type magma chamber during the initiation of early Tertiary sea floor spreading in the North Atlantic.
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Artemenko, G. V., and V. I. Ganotskiy. "Gabbroides of Peterman island (West Antarctica). First information on geochemistry." Arctic and Antarctic Research 65, no. 4 (December 19, 2019): 449–61. http://dx.doi.org/10.30758/0555-2648-2019-65-4-449-461.
Full textAbstract:
Peterman Island is located in the archipelago of the Wilhelm Islands on the west coast of the Antarctic Peninsula (Graham Land). It is composed of gabbroids and granitoids of the Andean complex, which formed almost 100 million years later than the volcanic group of the Antarctic Peninsula. To clarify their genesis and geodynamic conditions of formation, gabbroids of the Andean complex are of particular interest, since the petrological models of their formation are well developed. Gabbroid intrusions comprise small bodies that are widespread along the Antarctic Peninsula. Among them stand out olivine gabbros, normal gabbros, norites and hornblende gabbros. Also are found small bodies of melanogabbro-pegmatites and intramagmatic dykes, that are associated with the manifestations of ore mineralization of magnetite, ilmenite and sulfides. For this reason, they are of interest for both the minerals search and for solving the question of their genesis. To this end, we performed geochemical studies of Peterman Island gabbroids. Gabbroids of Peterman Island are represented by amphibolized medium-grained gabbro with hypidiomorphic texture. Among them, xenoliths of thinly stratified gabbroids 3 × 8 m in size were found, which are characteristic of stratified intrusions, for example, Stillwater, Bushveld, etc. Gabbroids of Peterman Island have low content of silica and potassium and according to the petrochemical characteristics correspond to peridotite gabbro. They have low contents of Cr, Ni, V and high strength lithophilic Y and Nb elements. Gabbroids have been crystallized from basic magma, differentiated in the intermediate crustal magma chambers. Positive anomalies of Sr, Eu, and Ti in the multielement diagrams and positive anomalies of europium Eu/Eu* suggest the accumulation of plagioclase and apparently, ilmenite in the magmatic chamber. The primary magma source for gabbroids was probably the primitive mantle (PM). Gabbroids are contaminated with crustal matter. This contamination is probably due to their regressive metamorphism, caused by the introduction of later intrusions of Andean complex granitoid. Finely layered xenolithic gabbroids do not differ from other homogeneous gabbros of Peterman Island in terms of chemical composition.This xenolith most likely represents a part (fragment) of the wall of the magma chamber in which the differentiation of the initial main magma took place. According to the obtained geochemical data, a wide range of compositions of the Andean complex gabbroids formed as a result of crystallization differentiation of magma melted from rocks of the composition of the primitive mantle (PM) in crustal magma chambers, which also resulted in the accumulation of ore elements — V, Co, and Cu in the residual magmatic melts.
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Ng, C. W. W., C. E. Choi, A. Y. Su, J. S. H. Kwan, and C. Lam. "Large-scale successive boulder impacts on a rigid barrier shielded by gabions." Canadian Geotechnical Journal 53, no. 10 (October 2016): 1688–99. http://dx.doi.org/10.1139/cgj-2016-0073.
Full textAbstract:
Debris flows occur in multiple surges. Boulders entrained within the flow have been reported to incapacitate structures within its flow path. Single-layer cushions, such as gabions, are often installed to shield debris-resisting barriers from boulder impact. However, most relevant works only focus on single impact and the performance of gabions subjected to successive loading is still not well understood. A new large-scale pendulum facility was established to induce impact energy of up to 70 kJ on an instrumented rigid barrier shielded by 1 m thick gabions. The response of the gabions under six successive impacts was investigated. Results show that the peak boulder impact force given by the Hertz equation is at least four times the measured values. The recommended load-reduction factor (Kc) used in practice can be reduced by a factor of two. After six successive impacts at an energy level of 70 kJ, the transmitted force increases by up to 40%. Based on the Swiss guidelines, a 13% increase of gabion thickness is required when successive impacts are concerned. The results presented in this paper will be useful for practitioners designing rigid barriers.
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O'Driscoll, B. "The Centre 3 layered gabbro intrusion, Ardnamurchan, NW Scotland." Geological Magazine 144, no. 6 (September 21, 2007): 897–908. http://dx.doi.org/10.1017/s0016756807003846.
Full textAbstract:
AbstractDetailed remapping of the Palaeogene Ardnamurchan Centre 3 gabbros, NW Scotland, suggests that this classic sequence of ring-intrusions forms a composite layered lopolith. The area mapped by previous studies as the Great Eucrite gabbro intrusion comprises 70% by area of Centre 3. Field observations suggest that most of the other smaller ring-intrusions of Centre 3 (interior to the Great Eucrite) constitute either distinct petrological facies of the same intrusion, or included country-rock or peridotite blocks. These observations, together with syn-magmatically deformed inward-dipping modal layering, are used here to support the interpretation that significant central sagging occurred in the intrusion at a late stage in its crystallization history.
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Dumańska-Słowik, Magdalena, and Wiesław Heflik. "Ultramafic and Mafic Rocks Found in the Near Vicinity of Mariupolites within the Alkaline Oktiabrski Massif (SE Ukraine) – Preliminary Investigations." Gospodarka Surowcami Mineralnymi 32, no. 2 (June 1, 2016): 63–78. http://dx.doi.org/10.1515/gospo-2016-0015.
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AbstractThe preliminary results of the mineralogical and geochemical investigations of ultramafic (peridotite and pyroxenite) and mafic (olivine gabbro) rocks from the Mazurovski Field of the Oktiabrski Massif in South-eastern Ukraine are presented in this paper. Peridotite is mainly composed of olivine (forsterite), pyroxene (diallage), plagioclase (labradorite) and ore minerals such as magnetite, ilmenite and pyrite. Antigorite and talk are secondary components. Diallage with subordinate plagioclase, olivine and Fe compounds (oxides/sulphides) are found in pyroxenite. Gabro is made of two generations of plagioclase, diallage, olivine, biotite and amphiboles (hornblende and actinolite). Chlorite, talk and ore minerals (ilmenite, pyrite, Fe oxides/hydroxides) occur as its subordinate components. On the basis of their mineral composition peridotite was classified as wehrlite, pyroxenite as clinopyroxenite, whereas the mafic rocks are represented by olivine gabbro. The mafic rocks are most likely products orginating from calc-alkaline magma. Owing to the fact that chromite was not identified in periodite, it is very probable that this rock is loco-temperature differentation product of ultramorfic rocks. The ultrabasic rocks and enriched with Al2O3, CaO and Fe and complethy impoverished of REES and alkalis. Only one olivine gabbro shows some amounts of REEs (0.096 wt.% REEs with the distinct predominance of LREE over HREE) and alkalis (2.89–4.0 wt.% Na2O + K2O), which are surely genetically associated with alkaline rocks occurring in the near vicinity of the ultramafic and mafic rocks of the Oktiabrski Massif. The enrichment of gabbro in REEs and alkalis most probably proceeded post-magmatic activity.
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Nakazawa, Hiroshi, Kazuya Usukura, Tadashi Hara, Daisuke Suetsugu, Kentaro Kuribayashi, Tsuyoshi Nishi, Shun Kimura, and Shoji Shimomura. "Problems in Earthquake Resistance Evaluation of Gabion Retaining Wall Based on Shake Table Test with Full-Scale Model." Journal of Disaster Research 14, no. 9 (December 1, 2019): 1154–69. http://dx.doi.org/10.20965/jdr.2019.p1154.
Full textAbstract:
The earthquake (Mw 7.3) that struck Nepal on April 25, 2015 caused damage to many civil engineering and architectural structures. While several road gabion retaining walls in mountainous regions incurred damage, there was very little information that could be used to draw up earthquake countermeasures in Nepal, because there have been few construction cases or case studies of gabion structures, nor have there been experimental or analytical studies on their earthquake resistance. Therefore, we conducted a shake table test using a full-scale gabion retaining wall to evaluate earthquake resistance. From the experiments, it was found that although gabion retaining walls display a flexible structure and deform easily due to the soil pressure of the backfill, they are resilient structures that tend to resist collapse. Yet, because retaining walls are assumed to be rigid bodies in the conventional stability computations used to design them, the characteristics of gabions as flexible structures are not taken advantage of. In this study, we propose an approach to designing gabion retaining walls by comparing the active collapse surface estimated by the trial wedge method, and the experiment results obtained from a full-scale model of a vertically-stacked wall, which is a structure employed in Nepal that is vulnerable to earthquake damage. When the base of the estimated slip line was raised for the trial wedge method, its height was found to be in rough agreement with the depth at which the gabion retaining wall deformed drastically in the experiment. Thus, we were able to demonstrate the development of a method for evaluating the seismic stability of gabion retaining walls that takes into consideration their flexibility by adjusting the base of the trial soil wedge.
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LINDH, ANDERS, ULF BERTIL ANDERSSON, THOMAS LUNDQVIST, and STEFAN CLAESSON. "Evidence of crustal contamination of mafic rocks associated with rapakivi rocks: an example from the Nordingrå complex, Central Sweden." Geological Magazine 138, no. 4 (July 2001): 371–86. http://dx.doi.org/10.1017/s0016756801005672.
Full textAbstract:
Gabbro and leucogabbro are volumetrically important rocks in the Nordingrå rapakivi complex, East Central Sweden. Plagioclase, ortho- and clinopyroxenes, and olivine dominate the gabbro. Perthitic orthoclase and quartz are interstitial in relation to the major minerals. The present work is based on 232 major-element and a large number of trace element analyses together with 15 whole rock Sm–Nd isotope analyses of the Nordingrå gabbroic rocks. εNd(T) values are negative, −1.1 to −3.2; the most negative values come from the gabbro. Most rocks are enriched in iron, some extremely enriched; none represent primitive mantle melts. The range of Mg-numbers is the same in the gabbro and the leucogabbro. Plots of the Ni-content vs. the Mg-number are scattered, but there is a positive correlation between these two parameters. The primary mantle-normalized ratios between similar trace elements are normally strongly different from one. Values larger as well as smaller than one are found for the same ratio in different rocks. The rare earth elements are only weakly fractionated with small Eu anomalies, negative for the gabbros and positive for the leucogabbros. The primary magma of the Nordingrå gabbro-anorthosite is thought to have been derived from a mildly depleted mantle source. Variations in the degree of partial melting of a reasonably homogeneous enriched mantle do not explain the observed chemical evolution. Crystal differentiation can account for some geochemical features, especially the Fe-enrichment. Crustal contamination is required by other characteristics as, for example, the negative εNd(T) values and the irregular and sometimes high primary-mantle normalized incompatible trace-element ratios. Al-rich relic material from the formation of the rapakivi granite melt is another source of assimilation. Most probably contaminants are heterogeneous, including undepleted crust (represented, for example, by early Svecofennian and Archaean granitoids), depleted crust (restitic after rapakivi magma extraction), and to some degree the associated rapakivi magma itself. Significant parts of this crust should be Archaean in age.
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ROBERTS, R. J., F. CORFU, T. H. TORSVIK, L. D. ASHWAL, and D. M. RAMSAY. "Short-lived mafic magmatism at 560–570 Ma in the northern Norwegian Caledonides: U–Pb zircon ages from the Seiland Igneous Province." Geological Magazine 143, no. 6 (September 18, 2006): 887–903. http://dx.doi.org/10.1017/s0016756806002512.
Full textAbstract:
The Seiland Igneous Province (SIP) of northern Norway comprises a suite of mainly gabbroic plutons, with subordinate ultramafic, syenitic and felsic intrusions. Several intrusions from the Seiland Igneous Province have been dated by ID-TIMS U–Pb zircon and monazite analyses. The Hasvik Gabbro on the island of Sørøy, previously assigned an age of 700±33 Ma by Sm–Nd, yields a U–Pb zircon age of 562±6 Ma, within error of the Storelv Gabbro (569±5 Ma) and a diorite associated with the Breivikbotn Gabbro (571±4 Ma). Various intrusions on the Øksfjord peninsula give nearly identical ages of 565±9 Ma (gabbro), 566±4 Ma (monzonite), 565±5 Ma (monzodiorite), 570±9 Ma (norite), and 566±1 Ma (orthopyroxenite). These ages overlap with those from Sørøy, and define a single and short-lived period of gabbroic (to felsic) magmatism for the region between 570 and 560 Ma, pre-dating a subordinate episode of alkalic magmatism at 530–520 Ma. The U–Pb ages contradict the previous geochronological interpretation for the Finnmark area, which implied a period of 250 m.y. for the emplacement of the SIP intrusions. The new age data also clearly distinguish the Seiland intrusions, emplaced into the Sørøy Group metasediments of the Kalak Nappe Complex, from several older granitic intrusions (c. 850 to 600 Ma) that cut the Sørøy Group farther east and south. The coincident ages of the different Seiland intrusive bodies also contradict the previous structural model for the area, which posits that the different gabbro bodies were emplaced at intervals, with compressional deformation affecting the gabbros between periods of intrusion. The short time span between the main plutonic phases strongly suggests that the mechanism for the emplacement of mafic magma operated in a single, probably extensional, tectonic regime. The mafic intrusions were later deformed and metamorphosed to at least amphibolite facies, most likely by the Scandian (420 Ma) phase of the Caledonian Orogeny.
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Spray, John G., and Gregory R. Dunning. "A U/Pb age for the Shetland Islands oceanic fragment, Scottish Caledonides: evidence from anatectic plagiogranites in ‘layer 3’ shear zones." Geological Magazine 128, no. 6 (November 1991): 667–71. http://dx.doi.org/10.1017/s0016756800019762.
Full textAbstract:
AbstractHigh precision U/Pb data obtained from zircons extracted from plagiogranite within the gabbro unit of the Shetland Islands oceanic fragment of northeast Scotland yield an age of 492 ± 3 Ma. Field relations indicate that the plagiogranites were generated by the partial melting of amphibolitized gabbros within high-temperature shear zones formed due to crustal deformation and fluid infiltration occurring in proximity to a spreading centre. The U/Pb data therefore constrain the crystallization age of the Shetland complex. This age is similar to U/Pb ages obtained from the Leka (497±2 Ma), Karmoy (493+7-4 Ma) and Gulfjellet (489±3 Ma) oceanic fragments of the Norwegian Caledonides, and the Pipestone Pond (4943-2 Ma) and Betts Cove (4893-2 Ma) oceanic fragments of the Canadian Appalachians.
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Wadsworth, W. J. "Silicate mineralogy of the Behelvie cumulates, N E Scotland." Mineralogical Magazine 55, no. 378 (March 1991): 113–19. http://dx.doi.org/10.1180/minmag.1991.055.378.09.
Full textAbstract:
AbstractUltramafic, troctolitic and gabbroic rocks at the northern end of the Belhelvie layered intrusion display progressive cryptic variation over a stratigraphic thickness of approximately 800 m in steeply-dipping cumulates, which young from W to E. This variation is shown by olivine (Fo87−77), orthopyroxene (En87−79), clinopyroxene (Ca45Mg48Fe7 to Ca44.5Mg45.5Fe10) and plagioclase (An81−75). The Belhelvie succession is believed to be equivalent to the poorly-exposed and structurally complex Insch Lower Zone. A laterally impersistent hypersthene-gabbro unit within the main sequence is re-interpreted as a downfaulted block of slightly more evolved cumulates. A repeat sequence of peridotites, troctolites and gabbros on the eastern side of the intrusion, and separated from the underlying main succession by a thin septum of country rock, is believed to represent a fresh influx of magma.
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Snachev, Vladimir I., Aleksandr V. Snachev, and Boris A. Puzhakov. "Geology, physical-chemical and geodynamic conditions for the formation of Sokolovsk and Krasnokamensk granitoid massifs (South Ural)." Georesursy 23, no. 1 (March 30, 2021): 85–93. http://dx.doi.org/10.18599/grs.2021.1.9.
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The article describes the geological structure of the Sokolovsk and Krasnokamensk massifs located in the central part of the Western subzone of the Chelyabinsk-Adamovka zone of the Southern Urals. They are of Lower Carboniferous age and break through the volcanogenic-sedimentary deposits of the Krasnokamensk (D3kr) and Bulatovo (S1-D1bl) strata. It was found that these intrusions belong to the gabbro-syenite complex and are composed of gabbroids (phase I) and syenites, quartz monzonites, less often monzodiorites (phase II). The rocks of the second phase predominate (90–95%). Gabbros belong to the normal alkaline series of the sodium series and are close to tholeiitic mafic rocks, the formation of which is associated with riftogenic structures; syenites correspond to moderately alkaline series with K-Na type of alkalinity. It has been proved that in terms of their petrographic, petrochemical, geochemical, and metallogenic features (content of TiO2, K2O, Na2O, Rb, Sr, distribution of REE, the presence of skarn-magnetic mineralization), the rocks of the massifs under consideration undoubtedly belong to the gabbro-granite formation. Crystallization of the Sokolovsk and Krasnokamensk intrusions occurred at a temperature of 880–930 °С in the mesoabyssal zone at a depth of about 7–8 km (P = 2.2–2.4 kbar). At the postmagmatic stage, the transformation parameters of the initially igneous rocks were, respectively, T = 730–770 °C, P = 4.0–4.2 kbar. The fact that these massifs belong to the gabbro-granite formation makes it possible to include them, together with Bolshakovsk, Klyuchevsky, Kurtmaksky and Kambulatovo, into the Chelyabinsk-Adamovka segment of the South Ural Early Carboniferous rift system.
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Pe-Piper, Georgia. "Mineralogy of an Appinitic Hornblende Gabbro and Its Significance for the Evolution of Rising Calc-Alkaline Magmas." Minerals 10, no. 12 (December 3, 2020): 1088. http://dx.doi.org/10.3390/min10121088.
Full textAbstract:
The magmatic and sub-solidus evolution of calcic amphiboles and Fe–Ti oxides was investigated in the Neoproterozoic Frog Lake pluton, Nova Scotia, Canada, in order to understand the relationship between the history of hydrous magma and the resulting mineralogy. The pluton occurs as sheet-like bodies of hornblende gabbro and hornblendite, with lesser tonalite dykes and granite bodies, interlayed with screens of medium-grade metamorphic country rock. Small, diffuse clots of felsic minerals are present in the gabbro. The subsolidus growth of actinolite occurs in early clinopyroxenes and amphiboles. Ilmenite is the dominant Fe–Ti oxide, as interstitial magmatic crystals. The increase of Mn towards the margin of the ilmenite crystals indicates a gradual increase in oxygen fugacity with time, leading to the precipitation of titanite and ferrohypersthene. The replacement of titanite by ilmenite and ilmenite lamellae in the amphiboles suggests subsequent reducing conditions during the sub-solidus crystallisation. The gabbros in the coeval, but apparently shallower, Jeffers Brook granodiorite laccolith have dominant magnetite and Mg-rich subsolidus amphiboles, which are indicative of high oxygen fugacity. The differences between the two plutons suggest that there was a greater flux of hydrothermal water through the sheet-like architecture of the Frog Lake pluton.
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You, Minxin, Wenyuan Li, Houmin Li, Zhaowei Zhang, and Xin Li. "Petrogenesis and Tectonic Significance of the ~276 Ma Baixintan Ni-Cu Ore-Bearing Mafic-Ultramafic Intrusion in the Eastern Tianshan Orogenic Belt, NW China." Minerals 11, no. 4 (March 26, 2021): 348. http://dx.doi.org/10.3390/min11040348.
Full textAbstract:
The Baixintan mafic-ultramafic intrusion in the Dananhu-Tousuquan arc of the Eastern Tianshan orogenic belt is composed of lherzolite, olivine gabbro, and gabbro. Olivine gabbros contain zircon grains with a U-Pb age of 276.8 ± 1.1 Ma, similar to the ages of other Early Permian Ni-Cu ore-bearing intrusions in the region. The alkaline-silica diagrams, AFM diagram, together with the Ni/Cu-Pd/Ir diagram, indicate that the parental magmas for the Baixintan intrusion were likely high-Mg tholeiitic basaltic in composition. The Cu/Pd ratios, the relatively depleted PGEs and the correlations between them demonstrate that the parental magmas had already experienced sulfide segregation. The lower CaO content in pyroxenites compared with the Duke Island Alaskan-type intrusion and the composition of spinels imply that Baixintan is not an Alaskan-type intrusion. By comparing the Baixintan intrusion with other specific mafic-ultramafic intrusions, this paper considers that the mantle source of the Baixintan intrusion is metasomatized by subduction slab-derived fluids’ components, which gives rise to the negative anomalies of Nb, Ti, and Ta elements. Nb/Yb-Th/Yb, Nb/Yb-TiO2/Yb, and ThN-NbN plots show that the Baixintan intrusion was emplaced in a back-arc spreading environment and may be related to a mantle plume.
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Nakazawa, Hiroshi, Tsuyoshi Nishi, Hiroyuki Kurihara, Daisuke Suetsugu, and Tadashi Hara. "Basic Study on Deformation Evaluation of Steel Wire Mesh for Rational Gabion Structure Design." EPI International Journal of Engineering 2, no. 2 (August 31, 2019): 109–15. http://dx.doi.org/10.25042/epi-ije.082019.04.
Full textAbstract:
Gabion structures are used in a variety of ways in Japan and around the world because they allow for the creation of simple structures at highly reasonable construction costs and completion periods. Previous earthquake damage surveys have shown that, in many cases, gabion structures did not collapse even though deformation was allowed, and have demonstrated that the wire mesh used in their construction has a high confinement effect on the stones filling the gabion. Despite this, gabions have not been actively utilized, nor have they been used to construct permanent structures in Japan because the design and construction of such structures are based on experience, and a standardized design method has not been developed. Hence, in order to facilitate development a design method for gabion-based structures, we must first go back to the basics and establish a detailed explanation of the wire mesh deformation mechanism of such structures. In this study, we performed tensile tests on wire meshes of different shapes in order to determine their strength and deformation characteristics and then conducted numerical analyses using the results obtained. The tensile tests revealed that deformation characteristics differed depending on the mesh shape and tensile direction. We also showed that the direction in which the tension acts and the mesh nodes are important, and that the test results could be reproduced via numerical analysis with the finite element method by using beam elements.
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Yazgan, Evren, and Roger Mason. "Orbicular gabbro from near Baskil, southeastern Turkey." Mineralogical Magazine 52, no. 365 (April 1988): 161–73. http://dx.doi.org/10.1180/minmag.1988.052.365.03.
Full textAbstract:
AbstractThe first occurrence of orbicular rocks in Turkey is reported. They are gabbros in a dyke in the Baskil island-arc magmatic suite, of the southern branch of the Alpine-Himalayan chain. The orbicules have lithologically varied cores, regular shells of troctolitic composition, with a radial arrangement of olivine and plagioclase crystals, and a matrix of vari-textured gabbro. Rock and mineral analyses indicate that magmatic crystallization began near the inner margin of the troctolitic shells. Metamorphic hydration of minerals in cores, shells and matrix followed directly after the later stages of magmatic crystallization, as part of a continuous process, and thus a magmatic-metamorphic origin for the orbicules is proposed. Alternative hypotheses for the development of the orbicules are discussed: one involving the development of a protocrystalline magma shell, the other rapid crystallization during upward migration of xenolith-bearing magma.
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Ngounouno, Ismaila, Christian Moreau, Bernard Deruelle, Daniel Demaiffe, and Raymond Montigny. "Petrologie du complexe alcalin sous-sature de Kokoumi (Cameroun)." Bulletin de la Société Géologique de France 172, no. 6 (November 1, 2001): 675–86. http://dx.doi.org/10.2113/172.6.675.
Full textAbstract:
Abstract The Cameroon Line was created by the rejuvenation, at the beginning of the opening of the Atlantic Ocean, of a Pan-African N070 degrees E fracture zone [Moreau et al., 1987], which acted as a huge lithospheric crack taping a hot asthenospheric zone [Deruelle et al., 1998; Marzoli et al., 2000]. The Kokoumi anorogenic pluton belongs to the E-W Garoua rift structure, which represents the easternmost extension of the Benue trough. The Garoua rift opened during the Neocomian-Lower Aptian ages [Benkhelil, 1988] through the rejuvenation of Pan-African normal faults. The rift subsided, was partially filled by conglomerates and sandstones, and the ensemble was folded in the Cretaceous period [Guiraud, 1993]. Post-Cretaceous faulting affected these sediments. Intrusion of the Kokoumi anorogenic complex through the Cretaceous sandstones was favoured by N-S, N070 degrees E, E-W and N135 degrees E faults and N030 degrees E extension [Moreau et al., 1987]. The Kokoumi complex was first described by Koch [1959]. It is composed of a plutonic gabbro-nepheline monzosyenite-nepheline syenite series and of lamprophyric dykes (monchiquites and camptonites). One trachyte dyke is also observed. The gabbros are olivine (Fo 70 )-, nepheline-, or kaersutite-bearing gabbros. They also contain Ti-Al-rich diopside, Ti-rich biotite, titanite, ilmenite, Ti-magnetite and apatite. The nepheline monzosyenites contain diopside, Fe-diopside, kaersutite, Fe-kaersutite, titanite and apatite. The nepheline syenites contain aegirine-augite, F-rich arfvedsonite and aenigmatite. Kaersutite and clinopyroxene predominate in the lamprophyres. Monchiquites and gabbros, camptonites and monzosyenites, display respective similar mineralogy. Monchiquites contain carbonate ocelli. The trachyte does not contain ferromagnesian minerals. For gabbros and monchiquites, equilibrium Fe-Ti oxide temperatures are between 650 and 750 degrees C (+ or -40 degrees C) and oxygen fugacities between 10 (super -15) and 10 (super -14) (+ or -0.5 X 10 (super -15) ) atmospheres, according to Spencer and Lindsley [1981]. Nepheline crystallized below 700 degrees C, according to Hamilton [1961]. All the rocks (except the trachyte) are nepheline normative (Ne 6 to Ne 40 ). Major and trace element distributions in MgO-element diagrams for the two series merge together into a single trend, from monchiquites to nepheline syenites. Nevertheless, the monchiquites trends have different slopes. We deduce the evolution from gabbros to nepheline syenites on the one hand and from monchiquites to camptonites on the other from primitive mantle normalized multi-element diagrams. Multi-element diagrams for the trachyte and the nepheline syenite are strictly similar. Patterns for Kokoumi gabbros are similar to those for basalts of the Kapsiki plateau [Ngounouno et al., 2000] and the Garoua rift [Ngounouno et al., 1997] with typical negative K and positive Zr and Ti anomalies. Patterns for nepheline monzosyenites display negative anomalies in Sr, P, Eu and Ti and those for nepheline syenites and trachyte display greater anomalies in these elements and Ba. Compared to gabbros, nepheline monzosyenites are enriched in all REE with a concave upward pattern and no Eu-anomaly. Nepheline syenites have a range of broadly similar REE patterns to nepheline monzosyenites with steep slope from La to Sm, strong Eu negative anomaly (Eu/Eu (super *) nearly equal 0.15) and heavy-REE spoon-shape. REE patterns for monchiquites, camptonites, and trachyte are respectively similar to those for gabbros, monzosyenites, and nepheline syenite. Initial Sr-isotope ratios of 0.7033 (recalculated from the measured ratios for an age of 39 Ma for plutonic rocks and 20 Ma for the lamprophyres and the trachyte) are similar to those obtained for basalts from the continental segment of the Cameroon Line [Halliday et al., 1988; Ngounouno et al., 2000; Demaiffe et al., unpubl.], whereas nepheline syenites and trachyte are distinctly more radiogenic with values between 0.7128 and 0.7251. Amphibole and whole-rock K-Ar analyses (table III) yield 39.0+ or -0.9 Ma and 36.6+ or -0.9 Ma respectively. Since amphibole is a reliable chronometer in K-Ar dating, we propose the first age as the probable time of emplacement of the gabbros. Whole-rock analysis of nepheline syenite 99 displays an age of 33.1+ or -0.5 Ma. Field and geochemical observations suggest that gabbros and nepheline syenite are cogenetic and hence contemporaneous.
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Nguyen, Du Khac, and Tomoaki Morishita. "Petro-geochemical characteristics and origin of the quartz in the lower oceanic crust, example from IODP-Hole U1473A." Journal of Mining and Earth Sciences 61, no. 4 (August 31, 2020): 67–74. http://dx.doi.org/10.46326/jmes.2020.61(4).07.
Full textAbstract:
IODP-Hole U1473A was drilled on the summit of Atlantis bank, Southwest Indian Ridge recovered large amounts of gabbroic rocks including mainly olivine gabbro. Felsic rocks are minor, approximately 1,5% of the total volume, which are comprising significant amount of quartz in some samples. The Ti concentrations and the estimated temperatures of the quartz in veins are relatively high, ranging from 30÷130 ppm and 540÷7000C, coupled with the myrmekitic textures in some veins are unambigeous evidence for the late magmatic origin. In addition to the crystallization mechanism in free spaces, such as crack/ fracture systems during the penetration of SiO2 - saturated magmas; the quartz is also formed by re-precipitation process at the same location leaving behind after the previous olivine in the host gabro has been dissolved.
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KHALATBARI JAFARI, MORTEZA, HADI SEPEHR, and KATAYOUN MOBASHER. "Tectonomagmatic evolution of the South Dehshir Ophiolite, Central Iran." Geological Magazine 153, no. 4 (October 7, 2015): 557–77. http://dx.doi.org/10.1017/s0016756815000618.
Full textAbstract:
AbstractThe South Dehshir Ophiolite, exposed along the southwestern margin of the Central Iranian microcontinent, comprises a mantle and a crustal sequence. This massif contains serpentinized peridotites, gabbros and diabase sheeted dykes cutting across wherlite, pegmatitic gabbro and plagiogranite, and is tectonically covered by radiolarites, pelagic limestones with Late Cretaceous microfauna and lavas. Under a microscope, the gabbros exhibit mesocumulate, adcumulate and hetradcumulate textures presumably formed in open magma chambers. Hypabyssal and lava samples show tholeiitic to calc-alkaline affinities, and their compositions cluster in the fields of arc or supra-subduction zone magmatism. Binary diagrams display compositional trends of magmatic differentiation, plotting away from the mid-ocean-ridge basalt (MORB) (tholeiitic) trend and following the arc (calc-alkaline) trend. Rare Earth element (REE) and spider diagrams display various enrichments at different levels. Moderate enrichment of the large-ion lithophile elements (LILE; Rb, Ba, Th, U, La, Sr) relative to the high-field-strength elements (HFSE; Nb, Ta) and slight depletion of Ti and Zr in some patterns may be attributed to variable influences of subduction components over the depleted mantle wedge. Elemental ratios display evidence for the contribution of both fluids and melt released from the subducted slab. Few patterns display ocean-island basalt (OIB) characteristics, possibly attributed to the involvement of local mantle plumes on the partial melting of the mantle wedge. This evidence indicates that the crustal rocks of the South Dehshir Ophiolite formed in a supra-subduction zone.