Master's Dissertation
DOI
https://doi.org/10.11606/D.44.1987.tde-21092015-150842
Document
Author
Full name
Maria de Lourdes Lazzari
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1987
Supervisor
Committee
Coutinho, Jose Moacyr Vianna (President)
Figueiredo, Mario Cesar Heredia de
Gomes, Celso de Barros
Title in Portuguese
O metabasito de Pirapora do Bom Jesus, SP
Keywords in Portuguese
Mineralogia
Petrografia
Abstract in Portuguese
Em Pirapora do Bom Jesus, SP, um corpo de rocha metabasítica ocorre em meio a metarenitos finos e, subordinadamente, metarcósio, metagrauvaca, filitos, dolomito, quartzito e itabirito. As rochas metabasíticas são compostas essencialmente de anfibólios e plagioclásios, tendo como acessórios: epidoto, clorita e titanita. O anfibólio tem composição actinolítica e o plagioclásio, albítica. São comparáveis quimicamente a outros metabasitos descritos na literatura, possuindo afinidade com basaltos toleíticos e de fundo oceânico. Grande parte das exposições de metabasito alterado nas colinas margeando o rio Tietê exibem estruturas de "pillow lava" com almofadas pouco deformadas ou deslocadas de sua posição original, com o pedúnculo para baixo e a superfície convexa para cima. Pelo comportamento químico dos minerais é possível concluir que os metabasitos se formaram em condições ajustadas à fácies xisto verde de Turner (1968). A temperatura metamórfica nestas rochas teve variação limitada ao intervalo de 300 a 450 'GRAUS' C.
Title in English
Not available.
Keywords in English
Not available.
Abstract in English
A metabasitic rock body occurs intercalated to finegrained metarenites and, subordinatedly, metaarkoses, metagreywackes, phyllites, dolomites, quartzites and itabirites in Pirapora do Bom Jesus, São Paulo satate. These metabasitic rocks are made up essentially by amphiboles and plagioclases, with epidote, chlorite and titanite as accessories. The amphibole has actinolitic, and the plagioclase, albitic compositions. They are chemically comparable to other metabasites quoted in the literature, sharing characteristics with tholeiitic and ocean-floor basalts. A great part of the altered metabasite exposures on the hillsides of the Tietê river pillow structures with pillows only slightly deformed or dislocated from their original position, with their cusps pointing downwards, and their convex surface upwards. The chemical behavior of the minerals permits to conclude that the metabasites underwent metamorphism under conditions comparable to those of the greenschist facies of turner (1968). The temperature of metamorphism in these rocks had a limited variation in the 300 to 450°C interval.
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Publishing Date
2015-09-23