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Previous issue date: 2011-07-28 / The final stage of Brasiliano/Pan-African orogeny in the Borborema Province is marked by
widespread plutonic magmatism. The Serra da Macambira Pluton is an example of such plutonism in
Serid? Belt, northeastern Borborema Province, and it is here subject of geological, petrographic,
textural, geochemical and petrogenetic studies. The pluton is located in the State of Rio Grande do
Norte, intrusive into Paleoproterozoic orthogneisses of the Caic? Complex and Neoproterozoic
metassupracrustal rocks of the Serid? Group. Based upon intrusion/inclusion field relationships,
mineralogy and texture, the rocks are classified as follows: intermediate enclaves (quartz-bearing
monzonite and biotite-bearing tonalite), porphyritic monzogranite, equigranular syenogranite to
monzogranite, and late granite and pegmatite dykes. Porphyritic granites and quartz-bearing
monzonites represent mingling formed by the injection of an intermediate magma into a granitic one,
which had already started crystallization. Both rocks are slightly older than the equigranular granites.
Quartz-bearing monzonite has K-feldspar, plagioclase, biotite, hornblende and few quartz, meanwhile
biotite-bearing tonalite are rich in quartz, poor in K-feldspar and hornblende is absent. Porphyritic
and equigranular granites display mainly biotite and rare hornblende, myrmekite and pertitic textures,
and zoned plagioclase pointing out to the relevance of fractional crystallization during magma
evolution. Such granites have Rare Earth Elements (REE) pattern with negative Eu anomaly and light
REE enrichment when compared to heavy REE. They are slight metaluminous to slight peraluminous,
following a high-K calc-alkaline path. Petrogenesis started with 27,5% partial melting of
Paleoproterozoic continental crust, generating an acid hydrous liquid, leaving a granulitic residue
with orthopyroxene, plagioclase (An40-50), K-feldspar, quartz, epidote, magnetite, ilmenite, apatite and
zircon. The liquid evolved mainly by fractional crystallization (10-25%) of plagioclase (An20), biotite
and hornblende during the first stages of magmatic evolution. Granitic dykes are hololeucocratic with
granophyric texture, indicating hypabissal crystallization and REE patterns similar to A-Type
granites. Preserved igneous textures, absence or weak imprint of ductile tectonics, association with
mafic to intermediate enclaves and alignment of samples according to monzonitic (high-K calcalkaline)
series all indicate post-collisional to post-orogenic complexes as described in the literature.
Such interpretation is supported by trace element discrimination diagrams that place the Serra da
Macambira pluton as late-orogenic, probably reflecting the vanishing stages of the exhumation and
collapse of the Brasiliano/Pan-African orogen. / O final da orog?nese Brasiliana/Pan-Africana na Prov?ncia Borborema, NE do Brasil, ?
marcado por um volumoso plutonismo. O pl?ton Serra da Macambira (PSM) constitui um exemplo
destes pl?tons, sendo aqui objeto de caracteriza??o geol?gica, petrogr?fica, textural, geoqu?mica e
petrogen?tica. O PSM localiza-se no Estado do Rio Grande do Norte, sendo intrusivo em ortognaisses
paleoproterozoicos (Complexo Caic?) e metassupracrustais neoproterozoicas (Grupo Serid?). As
rochas que comp?em o pl?ton foram classificadas segundo suas rela??es de intrus?o/inclus?o,
mineralogia e textura, na seguinte sequ?ncia relativa: enclaves intermedi?rios (quartzo monzonitos e
biotita tonalitos); monzogranitos porfir?ticos; sienogranitos e monzogranitos equigranulares; diques
gran?ticos e pegmat?ticos tardios. Granitos porfir?ticos e enclaves quartzo monzon?ticos representam
mistura de magmas (mingling), formada pela inje??o de um magma intermedi?rio em um magma
gran?tico j? em cristaliza??o. Ambos s?o ligeiramente precoces em rela??o ao granito equigranular. Os
enclaves quartzo monzon?ticos apresentam microclina, plagiocl?sio, biotita, hornblenda e pouco
quartzo, enquanto os biotia tonalitos s?o pobres em microclina, ricos em quartzo e n?o apresentam
hornblenda. Os granitos porfir?tios e equigranulares portam biotita e raramente hornblenda, texturas
mirmequ?tica e pert?tica, al?m de plagiocl?sios zonados que indicam a relev?ncia da cristaliza??o
fracionada na sua evolu??o. Estes granitos apresentam caracter?sticas geoqu?micas similares, com
anomalia negativa de Eu, enriquecimento em Elementos Terras Raras (ETR) leves e empobrecimento
em ETR pesados, variam entre ligeiramente metaluminosos e ligeiramente peraluminosos e seguem a
trajet?ria evolutiva c?lcio-alcalina de alto pot?ssio. Os processos petrogen?ticos tiveram in?cio com a
fus?o parcial (27,5%) da crosta continental paleoproterozoica, gerando um l?quido ?cido hidratado,
que incorporou H2O dos minerais existentes na fonte, deixando um res?duo granul?tico com
ortopirox?nio, K-feldspato, plagiocl?sio (An40-50), quartzo, ep?doto, magnetita, ilmenita, apatita e
zirc?o. O l?quido evoluiu com predomin?ncia do processo de cristaliza??o fracionada (10-25%),
ocorrendo fracionamento de plagiocl?sio s?dico (An20), biotita e hornblenda nas fases iniciais de
cristaliza??o. Diques ?cidos tardios apresentam textura granof?rica, caracterizando cristaliza??o e/ou
coloca??o em condi??es hipabissais e padr?o de ETR similares aos de granitos Tipo-A. Texturas
?gneas bem preservadas, aus?ncia ou fraca atua??o de eventos tect?nicos, associa??o de enclaves
intermedi?rios a m?ficos e alinhamento de amostras de acordo com s?ries de diferencia??o c?lcioalcalina
de alto pot?ssio s?o encontradas em complexos magm?ticos p?s-colisionais a p?s-orog?nicos
descritos na literatura. Esta interpreta??o est? em acordo com o comportamento das amostras em
diagramas discriminantes de ambientes tect?nicos, posicionando o pl?ton em um contexto tardiorog?nico,
eventualmente registrando os epis?dios finais de colapso da cadeia Brasiliana/Pan-Africana
na Faixa Serid?.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/18817 |
| Date | 28 July 2011 |
| Creators | Silva, Dalton Rosemberg Valentim da |
| Contributors | CPF:15603180404, http://lattes.cnpq.br/1259445348649589, Galindo, Antonio Carlos, CPF:08036845415, http://lattes.cnpq.br/9747727150782125, Mariano, Gorki, CPF:07019785387, http://lattes.cnpq.br/9480872229631779, Souza, Zorano Sergio de |
| Publisher | Universidade Federal do Rio Grande do Norte, Programa de P?s-Gradua??o em Geodin?mica e Geof?sica, UFRN, BR, Geodin?mica; Geof?sica |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Format | application/pdf |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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