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Master's Dissertation
DOI
10.11606/D.44.1995.tde-13102014-154544
Document
Author
Full name
Jose Maria Azevedo Sobrinho
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 1995
Supervisor
Committee
Girardi, Vicente Antonio Vitorio (President)
Janasi, Valdecir de Assis
Oliveira, Marcos Aurelio Farias de
Title in Portuguese
Petrologia dos charnockitos da região de Itariri (SP).
Keywords in Portuguese
Petrologia
Abstract in Portuguese
Na região de Itariri ocorrem rochas charnockíticas parcialmente migmatizadas, migmatitos, granada-biotita gnaisses, milonitos, da Zona de Cisalhamento de Itariri, além de ocorrências esparsas de gnaisses kinzigíticos, rochas calciossilicáticas, anfibolitos e diques básicos. O contato entre as rochas charnockíticas e os migmatitos é marcado por uma faixa aqui designada "Zona de Transição", onde os charnockitos são mais intensamente migmatizados. Já entre os charnockitos e as rochas metassedimentares o contato é brusco. A composição das rochas charnockíticas é predominantemente quartzo norítica a enderbítica, com variações para opdalitos e charnockitos sensu strictu. Frequentemente, essas rochas apresentam enclaves de granulitos básicos, por vezes boudinados, e eventualmente xenólitos de metaclinopiroxenitos. As análises químicas dos piroxênios das rochas charnockíticas e de seus enclaves básicos indicaram que as composições dos ortopiroxênios são pouco variadas, como 'En IND. 47-50' 'FS IND.48-51' 'WO IND.2' enquanto os clinopiroxênios variam no intervalo 'EN IND.34-36' 'FS IND. 19-21' 'WO IND.45-47'. Dados geotermométricos, para valores corrigidos, fornecem temperaturas médias do metamorfismo de grau alto da ordem de 759°C e 763°C, de acordo com os geotermômetros de Wood & Banno e Wells, respectivamente. As análises químicas de rocha total mostram que os charnockitos de Itariri fazem parte de uma sequência calcio-alcalina bimodal, típica de terrenos arqueanos, possivelmente associada a ambiente de subducção.
Title in English
Not available.
Keywords in English
Not available.
Abstract in English
The dominant rock types in the Itariri region are partially migmatized charnockitic rocks, migmatites, garnet biotite gneisses and Itariri Shear Zone milonites. Sparse occurrences of kinzigitic gneisses, calc-silicate rocks, amphibolites and basic dikes are also found. More intensively migmatized charnockites, here called "Transition Zone", mark the contact between the charnockitic rocks and the migmatites. The contact between the charnockites and the metasedimentary rocks is sharp. The composition of the charnockitic rocks is predominantly quartz noritic to enderbitic, with variations to opdalites and sensu strictu charnockites. Basic granulitic enclaves are frequent, usually as boudins. Metaclinopyroxenites xenolites also occur. Mineral analyses of pyroxenes from the charnockitic rocks and their basic enclaves show that the composition of orthopyroxenes hardly differ from 'En IND. 47-50' 'Fs IND.48-51' 'Wo IND.2', whereas clinopyroxenes composition vary in the 'En 34-36' 'Fs IND.19-21' 'Wo45-47' interval. Corrected geothermometric data yield high-grade metamorphism average temperatures of the order of 759° C and 763° C according to Wood & Banno and Wells geothermometers, respectively. Whole rock chemical data show that the Itariri charnockites belong to a bimodal calcalkaline sequence, typical of Archean terrains, possibly associated to a subduction environment.
 
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Publishing Date
2014-10-15
 
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