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| Gualda,Guilherme A.R.; Vlach,Silvio R.F.. |
| An important drawback of the electron microprobe is its inability to quantify Fe3+/Fe2+ ratios in routine work. Although these ratios can be calculated, there is no unique criterion that can be applied to all amphiboles. Using a large data set of calcic, sodic-calcic, and sodic amphibole analysis from A-type granites and syenites from southern Brazil, weassess the choices made by the method of Schumacher (1997, Canadian Mineralogist, 35: 238-246), which uses the average between selected maximum and minimum estimates. Maximum estimates selected most frequently are: 13 cations excluding Ca, Na, and K (13eCNK - 66%); sum of Si and Al equal to 8 (8SiAl - 17%); 15 cations excluding K (15eK - 8%). These selections are appropriate based on crystallochemical... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Amphiboles; Stoichiometry; Ferric iron; EPMA. |
| Ano: 2005 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652005000300012 |
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| Vlach,Silvio R.F.. |
| Epidote-group minerals, together with albite, quartz, fluorite, Al-poor and Fe-rich phyllosilicates, zircon, and minor oxides and sulphides, are typical hydrothermal phases in peralkaline alkali-feldspar granites from the Corupá Pluton, Graciosa Province, South Brazil. The epidote-group minerals occur as single crystals and as aggregates filling in rock interstices and miarolitic cavities. They display complex recurrent zoning patterns with an internal zone of ferriallanite-(Ce), followed by allanite-(Ce), then epidote-ferriepidote, and an external zone with allanite-(Ce), with sharp limits, as shown in BSE and X-ray images. REE patterns show decreasing fractionation degrees of LREE over HREE from ferriallanite to epidote. The most external allanite is... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Allanite; Epidote; Hydrothermal; Compositional variations; Peralkaline granite; Corupá Pluton; Graciosa Province. |
| Ano: 2012 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652012000200012 |
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| Gualda,Guilherme A.R.; Vlach,Silvio R.F.. |
| The Serra da Graciosa region includes important occurrences of granites and syenites of the Graciosa A-type Province (formerly Serra do Mar Suite), southern Brazil. Using fieldwork, petrography, and remote sensing imagery, we characterize the geology of the plutons in the region. Five individual plutons were recognized. Two correspond to the previously defined Marumbi and Anhangava Plutons. We divide the former "Graciosa Pluton" into three new plutons: Capivari, Órgãos, and Farinha Seca. The plutons are elliptical with northeast-southwest orientation. Two petrographic associations can be recognized: an alkaline association that includes peralkaline and metaluminous hypersolvus alkalifeldspar granites and syenites (Anhangava, Farinha Seca, Órgãos), and an... |
| Tipo: Info:eu-repo/semantics/article |
Palavras-chave: Serra da Graciosa; A-type granites and syenites; Graciosa Province; Paraná State. |
| Ano: 2007 |
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652007000300006 |
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