The petrology and geochemistry of the Nordeste volcanic complex, São Miguel, Azores

Detalhes bibliográficos
Autor(a) principal: Fernandez, Louis A.
Data de Publicação: 1982
Tipo de documento: Artigo
Idioma: eng
Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
Texto Completo: http://hdl.handle.net/10400.3/4906
Resumo: International Symposium on the Activity of Oceanic Volcanoes. Ponta Delgada, 4-9 August 1980.
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spelling The petrology and geochemistry of the Nordeste volcanic complex, São Miguel, AzoresGeochemistryPetrologySão Miguel Island (Azores)NordesteInternational Symposium on the Activity of Oceanic Volcanoes. Ponta Delgada, 4-9 August 1980.Sixty samples from the Nordeste Volcanic Complex, São Miguel, Azores, have been analyzed for major elements and fifteen for LIL and other trace metals. Analysis of magnesia and alkali-silica variation diagrams show the bulk of the Nordeste volcanics to be a potassic, mildly alkaline, alkali basalt → traohybasalrt → tristanite → trachyte series. The oldest flows of the complex, characterized by low TiO² and high SiO², are interpreted as representative of compositions transitional between tholeiitic and alkalic suites. All of the Nordeste samples are enriched in lighter REE relative to Mid-Atlantic Ridge Basalts from the Azores Plateau. Light REE enrichment factors range through a factor of ~ 5 between the basaltic types and the tristanites and trachytes. The younger Nordeste volcanics, when compared to the transitional basalts, are distinguished by higher concentrations of Ce, Rb, Ba, Eu, Lu, Hf, and Yb and higher La/Sm ratios. The transitional basalts are characterized by high T/Th and Ta/Hf ratios. Using major, minor and trace element compositions and microprobe analyses of phenocrystic and groundmass phases, least-squares calculations support a crystal fractionation model. The magnesian aphyric to ankaramitic alkali basalts represent magmas from which minor amounts of olivine and pyroxene were either removed from or incorporated into while residing in shallow crustal reservoirs. The trachybasalt → trachyte series represent fractionated liquids generated by the removal of titanaugite, plagioclase, olivine, titanomagnetite, and ilmenite in the early stages follwed by removal of abundant plagioclase, augite and minor opagues in the late stages. The dominance of plagioclase in the latter fractionation scheme and its rarity as an xenocrystic phase suggests fractionation in deeper reservoirs, now represented by gabbroic and dioritic layered complexes underlying the Azores Platform. The major and minor element composition of the transitional basalts precludes their being the parent of the alkali basalt sequence, but rather indicate two magma series geenrated by diferrent degrees of partial melting in the mantle.Universidade dos AçoresRepositório da Universidade dos AçoresFernandez, Louis A.2018-11-29T12:39:51Z1982-071982-07-01T00:00:00Zinfo:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/articleapplication/pdfhttp://hdl.handle.net/10400.3/4906engFERNANDEZ, Louis A. (1982). The petrology and geochemistry of the Nordeste volcanic complex, São Miguel, Azores. "Arquipélago. Série Ciências da Natureza", 3: 145-158.info:eu-repo/semantics/openAccessreponame:Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)instname:Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informaçãoinstacron:RCAAP2022-12-20T14:33:09Zoai:repositorio.uac.pt:10400.3/4906Portal AgregadorONGhttps://www.rcaap.pt/oai/openaireopendoar:71602024-03-19T16:27:13.817766Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos) - Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informaçãofalse
dc.title.none.fl_str_mv The petrology and geochemistry of the Nordeste volcanic complex, São Miguel, Azores
title The petrology and geochemistry of the Nordeste volcanic complex, São Miguel, Azores
spellingShingle The petrology and geochemistry of the Nordeste volcanic complex, São Miguel, Azores
Fernandez, Louis A.
Geochemistry
Petrology
São Miguel Island (Azores)
Nordeste
title_short The petrology and geochemistry of the Nordeste volcanic complex, São Miguel, Azores
title_full The petrology and geochemistry of the Nordeste volcanic complex, São Miguel, Azores
title_fullStr The petrology and geochemistry of the Nordeste volcanic complex, São Miguel, Azores
title_full_unstemmed The petrology and geochemistry of the Nordeste volcanic complex, São Miguel, Azores
title_sort The petrology and geochemistry of the Nordeste volcanic complex, São Miguel, Azores
author Fernandez, Louis A.
author_facet Fernandez, Louis A.
author_role author
dc.contributor.none.fl_str_mv Repositório da Universidade dos Açores
dc.contributor.author.fl_str_mv Fernandez, Louis A.
dc.subject.por.fl_str_mv Geochemistry
Petrology
São Miguel Island (Azores)
Nordeste
topic Geochemistry
Petrology
São Miguel Island (Azores)
Nordeste
description International Symposium on the Activity of Oceanic Volcanoes. Ponta Delgada, 4-9 August 1980.
publishDate 1982
dc.date.none.fl_str_mv 1982-07
1982-07-01T00:00:00Z
2018-11-29T12:39:51Z
dc.type.status.fl_str_mv info:eu-repo/semantics/publishedVersion
dc.type.driver.fl_str_mv info:eu-repo/semantics/article
format article
status_str publishedVersion
dc.identifier.uri.fl_str_mv http://hdl.handle.net/10400.3/4906
url http://hdl.handle.net/10400.3/4906
dc.language.iso.fl_str_mv eng
language eng
dc.relation.none.fl_str_mv FERNANDEZ, Louis A. (1982). The petrology and geochemistry of the Nordeste volcanic complex, São Miguel, Azores. "Arquipélago. Série Ciências da Natureza", 3: 145-158.
dc.rights.driver.fl_str_mv info:eu-repo/semantics/openAccess
eu_rights_str_mv openAccess
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dc.publisher.none.fl_str_mv Universidade dos Açores
publisher.none.fl_str_mv Universidade dos Açores
dc.source.none.fl_str_mv reponame:Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
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instname_str Agência para a Sociedade do Conhecimento (UMIC) - FCT - Sociedade da Informação
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