New method of semi-automatic modal analyses for phenocrysts of porphyritic rocks based on quantitative digital colour specification technique

Abstract

This paper proposes a new method for modal analyses of centimetric phenocrysts and porphyroblasts using a digital rock image. The dot matrix image of the rock is imported into vectorial draw software as background. The outline of all of the phenocrysts is ResumoO presente artigo propõe um novo método para análise modal de fenocristais e porfiroblastos de tamanho centimétrico a partir de imagem digital. A imagem matricial da rocha é importada para um software de desenho vetorial como background. O contorno de todos os fenocristais é marcado na overlay por curvas vetoriais fechadas, sendo sua área interna pintada em preto. Após esta operação, a imagem da rocha no background é retirada e o background é pintado em branco. Os objetos vetoriais compostos do background e a overlay são exportados como uma imagem matricial de formato BMP. A porcentagem das áreas pintadas em preto corresponde à quantidade modal dos fenocristais e essa quantidade é calculada por software para análise quantitativa de cores Wilbur. Esse método tem alta precisão no processamento gráfico. Entretanto a translucidez da massa fundamental pode causar incerteza na marcação vetorial dos fenocristais. Portanto este método é recomendado para rochas com fenocristais maiores do que 5 mm. Palavras-chave:Análise modal, imagem digital, fenocristal, porfiroblasto, Wilbur, especificação de cor.REM: R. Esc. Minas, Ouro Preto, 60(1

<b>Principle and geomorphological applicability of summit level and base level technique using Aster Gdem satellite-derived data and the original software Baz

“…The authors adopt Aster Gdem moderated by SRTM for the original topographic data, which are released from the United States Geological Survey. The virtual maps are constructed by the original software Baz version 1.0 (MOTOKI et al, 2012a) and Wilbur version 1.0 2007a). They run on the DOS platform by linecommand, so the operations are not familiar for Windows TM users.…”

“…The fission-track dating for apatite permits to estimate the total uplift vertical movement as ca. 3 km (MOTOKI et al, 2012b;2007b The summit level map is quite efficient for the areas of Quaternary tectonism. The neotectonic study of the Mount Rokko, Kobe, Japan (HUZITA; KASAMA, 1977), was a pioneer work using summit level technique.…”

“…State of Rio de Janeiro has more than 10 intrusive bodies of nepheline syenite and alkaline syenite (SICHEL et al, 2012), such as Itatiaia (BROTZU et al, 1997;PIRES et al, 2014), Morro Redondo (BROTZU et al, 1989, Serra de Tomases, Tinguá (DERBY, 1897), Mendanha (MOTOKI et al, 2007c), Itaúna , Tanguá, Rio Bonito, Soarinho , Morro dos Gatos (MOTOKI et al, 2012c;GERALDES et al, 2013), Morro de São João (BROTZU et al, 2007), and Cabo Frio Island (MOTOKI;MOTOKI et al, 2008c). Some of them accompany subvolcanic pyroclastic conduits and fissures (MOTOKI et al, 2007d;SICHEL et al, 2008b). All of them are intrusive pyroclastic bodies without extrusive bodies are observed (MOTOKI; MOTOKI et al, 2008d).…”

Gravimetric structure for the abyssal mantle massif of Saint Peter and Saint Paul peridotite ridge, Equatorial Atlantic Ocean, and its relation to active uplift

“…The distribution areas of the submarine morphologies have been measured by the pixel counting method (Motoki et al 2007(Motoki et al , 2012b, using the original software Wilbur ver. 1.0 (Motoki et al , 2006.…”

The pyroclastic dyke and welded crystal tuff of the Morro dos Gatos alkaline intrusive complex, State of Rio de Janeiro, Brazil

“…According to the digital photo analyses (Motoki et al, 2007e), the average contents of the clasts is about 30%, which corresponds to clast matrix-supported texture. The matrix is completely consolidated.…”