Subvolcanic vent-filling welded tuff breccia of Cabo Frio Island, State of Rio de Janeiro, Brazil
Autor(a) principal: | |
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Data de Publicação: | 2008 |
Outros Autores: | , , |
Tipo de documento: | Artigo |
Idioma: | eng |
Título da fonte: | REM. Revista Escola de Minas (Online) |
Texto Completo: | http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672008000400004 |
Resumo: | At the southwestern corner of Cabo Frio Island, State of Rio de Janeiro, Brazil, a pyroclastic body is present in an area of 500 x 600 m, intruding into the host orthogneiss with subvertical contact. Between the orthogneiss and pyroclastic body, there is a trachyte intercalation, 5 to 10 m wide. The pyroclastic rocks have a clast-matrix supported structure and the clast size ranges from 1 mm to 40 cm. Larger than 10 cm clasts are semi-rounded and those that are less than 5 cm are angular. They are composed mainly of trachyte, subordinately of orthogneiss, and eventually of welded tuff. The texture is heterogeneous and no grain-size sorting or volcanic layering of the clasts was observed. Microscopic observations have revealed hydrothermal alteration featured by calcite dissemination, alkaline feldspar sericitization, and mafic mineral decomposition. The matrix is filled by angular fragments of alkaline feldspar, quartz, plagioclase, and opaque minerals, smaller than 0.6 mm. The existence of the welded tuff clasts indicates that explosive eruptions took place repeatedly. The subvertical intrusive contact, small exposure area, rounded clasts, heterogeneous clast size, and absence of volcanic layering indicate that the pyroclastic rock is subvolcanic vent-filling welded tuff breccia, and not a constituent of a subaerial eruptive deposit. |
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Subvolcanic vent-filling welded tuff breccia of Cabo Frio Island, State of Rio de Janeiro, BrazilCabo Frio Islandsubvolcanic conduitpyroclastic rockwelded tuffsubvertical intrusive contactAt the southwestern corner of Cabo Frio Island, State of Rio de Janeiro, Brazil, a pyroclastic body is present in an area of 500 x 600 m, intruding into the host orthogneiss with subvertical contact. Between the orthogneiss and pyroclastic body, there is a trachyte intercalation, 5 to 10 m wide. The pyroclastic rocks have a clast-matrix supported structure and the clast size ranges from 1 mm to 40 cm. Larger than 10 cm clasts are semi-rounded and those that are less than 5 cm are angular. They are composed mainly of trachyte, subordinately of orthogneiss, and eventually of welded tuff. The texture is heterogeneous and no grain-size sorting or volcanic layering of the clasts was observed. Microscopic observations have revealed hydrothermal alteration featured by calcite dissemination, alkaline feldspar sericitization, and mafic mineral decomposition. The matrix is filled by angular fragments of alkaline feldspar, quartz, plagioclase, and opaque minerals, smaller than 0.6 mm. The existence of the welded tuff clasts indicates that explosive eruptions took place repeatedly. The subvertical intrusive contact, small exposure area, rounded clasts, heterogeneous clast size, and absence of volcanic layering indicate that the pyroclastic rock is subvolcanic vent-filling welded tuff breccia, and not a constituent of a subaerial eruptive deposit.Escola de Minas2008-12-01info:eu-repo/semantics/articleinfo:eu-repo/semantics/publishedVersiontext/htmlhttp://old.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672008000400004Rem: Revista Escola de Minas v.61 n.4 2008reponame:REM. Revista Escola de Minas (Online)instname:Escola de Minasinstacron:ESCOLA DE MINAS10.1590/S0370-44672008000400004info:eu-repo/semantics/openAccessSichel,Susanna EleonoraMotoki,AkihisaSavi,David CanabarroSoares,Rodrigoeng2009-01-29T00:00:00Zoai:scielo:S0370-44672008000400004Revistahttp://www.scielo.br/remhttps://old.scielo.br/oai/scielo-oai.phpeditor@rem.com.br1807-03530370-4467opendoar:2009-01-29T00:00REM. Revista Escola de Minas (Online) - Escola de Minasfalse |
dc.title.none.fl_str_mv |
Subvolcanic vent-filling welded tuff breccia of Cabo Frio Island, State of Rio de Janeiro, Brazil |
title |
Subvolcanic vent-filling welded tuff breccia of Cabo Frio Island, State of Rio de Janeiro, Brazil |
spellingShingle |
Subvolcanic vent-filling welded tuff breccia of Cabo Frio Island, State of Rio de Janeiro, Brazil Sichel,Susanna Eleonora Cabo Frio Island subvolcanic conduit pyroclastic rock welded tuff subvertical intrusive contact |
title_short |
Subvolcanic vent-filling welded tuff breccia of Cabo Frio Island, State of Rio de Janeiro, Brazil |
title_full |
Subvolcanic vent-filling welded tuff breccia of Cabo Frio Island, State of Rio de Janeiro, Brazil |
title_fullStr |
Subvolcanic vent-filling welded tuff breccia of Cabo Frio Island, State of Rio de Janeiro, Brazil |
title_full_unstemmed |
Subvolcanic vent-filling welded tuff breccia of Cabo Frio Island, State of Rio de Janeiro, Brazil |
title_sort |
Subvolcanic vent-filling welded tuff breccia of Cabo Frio Island, State of Rio de Janeiro, Brazil |
author |
Sichel,Susanna Eleonora |
author_facet |
Sichel,Susanna Eleonora Motoki,Akihisa Savi,David Canabarro Soares,Rodrigo |
author_role |
author |
author2 |
Motoki,Akihisa Savi,David Canabarro Soares,Rodrigo |
author2_role |
author author author |
dc.contributor.author.fl_str_mv |
Sichel,Susanna Eleonora Motoki,Akihisa Savi,David Canabarro Soares,Rodrigo |
dc.subject.por.fl_str_mv |
Cabo Frio Island subvolcanic conduit pyroclastic rock welded tuff subvertical intrusive contact |
topic |
Cabo Frio Island subvolcanic conduit pyroclastic rock welded tuff subvertical intrusive contact |
description |
At the southwestern corner of Cabo Frio Island, State of Rio de Janeiro, Brazil, a pyroclastic body is present in an area of 500 x 600 m, intruding into the host orthogneiss with subvertical contact. Between the orthogneiss and pyroclastic body, there is a trachyte intercalation, 5 to 10 m wide. The pyroclastic rocks have a clast-matrix supported structure and the clast size ranges from 1 mm to 40 cm. Larger than 10 cm clasts are semi-rounded and those that are less than 5 cm are angular. They are composed mainly of trachyte, subordinately of orthogneiss, and eventually of welded tuff. The texture is heterogeneous and no grain-size sorting or volcanic layering of the clasts was observed. Microscopic observations have revealed hydrothermal alteration featured by calcite dissemination, alkaline feldspar sericitization, and mafic mineral decomposition. The matrix is filled by angular fragments of alkaline feldspar, quartz, plagioclase, and opaque minerals, smaller than 0.6 mm. The existence of the welded tuff clasts indicates that explosive eruptions took place repeatedly. The subvertical intrusive contact, small exposure area, rounded clasts, heterogeneous clast size, and absence of volcanic layering indicate that the pyroclastic rock is subvolcanic vent-filling welded tuff breccia, and not a constituent of a subaerial eruptive deposit. |
publishDate |
2008 |
dc.date.none.fl_str_mv |
2008-12-01 |
dc.type.driver.fl_str_mv |
info:eu-repo/semantics/article |
dc.type.status.fl_str_mv |
info:eu-repo/semantics/publishedVersion |
format |
article |
status_str |
publishedVersion |
dc.identifier.uri.fl_str_mv |
http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672008000400004 |
url |
http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0370-44672008000400004 |
dc.language.iso.fl_str_mv |
eng |
language |
eng |
dc.relation.none.fl_str_mv |
10.1590/S0370-44672008000400004 |
dc.rights.driver.fl_str_mv |
info:eu-repo/semantics/openAccess |
eu_rights_str_mv |
openAccess |
dc.format.none.fl_str_mv |
text/html |
dc.publisher.none.fl_str_mv |
Escola de Minas |
publisher.none.fl_str_mv |
Escola de Minas |
dc.source.none.fl_str_mv |
Rem: Revista Escola de Minas v.61 n.4 2008 reponame:REM. Revista Escola de Minas (Online) instname:Escola de Minas instacron:ESCOLA DE MINAS |
instname_str |
Escola de Minas |
instacron_str |
ESCOLA DE MINAS |
institution |
ESCOLA DE MINAS |
reponame_str |
REM. Revista Escola de Minas (Online) |
collection |
REM. Revista Escola de Minas (Online) |
repository.name.fl_str_mv |
REM. Revista Escola de Minas (Online) - Escola de Minas |
repository.mail.fl_str_mv |
editor@rem.com.br |
_version_ |
1754122197186641920 |