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| Format: | Artículo científico |
| Language: | en |
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Academia Brasileira de Ciências
2007
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| Online Access: | https://www.redalyc.org/articulo.oa?id=32779412 |
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Table of Contents:
- Late sodic metasomatism evidences in bimodal volcanic rocks of the Acampamento Velho Alloformation, Neoproterozoic III, southern Brazil Delia Del Pilar M. de Almeida Vitor P. Pereira Adriane Machado Henrique Zerfass Ricardo Freitas Multidisciplinaria (Ciencias Naturales y Exactas) chemical mineral Brazilian Orogeny sodic metasomatism Acampamento Velho Alloformation A mineralogical study was carried out in mafic and felsic volcanic rocks of the Acampamento Velho Alloformationat Cerro do Bugio, Perau and Serra de Santa Bárbara areas (Camaquã Basin) in southern Brazil. The AcampamentoVelho bimodal event consists of two associations: lower mafic at the base and upper felsic at the top. Plagioclaseand alkali-feldspar were studied using an electronic microprobe, and magnetite, ilmenite, rutile, illite and alkalifeldsparwere investigated through scanning electron microscopy. The rocks were affected by a process of late sodicautometasomatism. In mafic rocks, Ca-plagioclase was transformed to albite and pyroxenes were altered. In felsicrocks, sanidine was partially pseudomorphosed, generating heterogeneous alkali-feldspar. In this association, unstableTi-rich magnetite was replaced by rutile and ilmenite. In mafic rocks, the crystallization sequence was: (1) Ti-richmagnetite (?), (2) pyroxene and Ca-plagioclase, (3) albite (alteration to Ca-plagioclase), (4) sericite, chlorite and calcite(alteration to pyroxene), and kaolinite (alteration to plagioclase/albite). In felsic rocks: (1) zircon, (2) Ti-rich magnetite,(3) sanidine, (4) quartz. The introduction of late Na-rich fluids, generated the formation of (5) heterogeneous alkalifeldspar,(6) ilmenite and rutile from the Ti-rich magnetite, (7) albite in the spherulites. Finally, alteration of sanidine,vitroclasts and pumice to (8) illite. 2007 artículo científico 0001-3765 https://www.redalyc.org/articulo.oa?id=32779412 en http://www.redalyc.org/revista.oa?id=327 Anais da Academia Brasileira de Ciências application/pdf Academia Brasileira de Ciências Anais da Academia Brasileira de Ciências (Brasil) Num.4 Vol.79