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Previous issue date: 2015-04-23 / A atividade plut?nica ediacarana, relacionada a orog?nese Brasiliana/Pan-Africana, constitui uma das mais importantes fei??es geol?gicas na Prov?ncia Borborema, representada em sua extens?o por in?meros bat?litos, stocks e diques. O Pl?ton Gran?tico Serra da Rajada (PGSR), principal objeto desse estudo, situado na por??o central do Dom?nio Rio Piranhas-Serid? representa um exemplo dessa atividade, sendo objeto de estudos cartogr?fico, petrogr?fico, litogeoqu?mico e geocronol?gico. Suas rochas s?o individualizadas em duas f?cies, sendo a f?cies gran?tica descrita como monzogranitos constitu?dos por K-feldspato, plagiocl?sio (oligocl?sico-An23-24%), quartzo e biotita (m?fico principal), tendo como minerais acess?rios opacos, titanita, allanita, apatita e zirc?o. Clorita, mica branca e carbonato s?o minerais de altera??o. A f?cies dior?tica compreende rochas formadas por quartzo diorito contendo plagiocl?sio (fase mineral dominante), quartzo e K-feldspato. Biotita e anfib?lio s?o os minerais m?ficos dominantes, e titanita, minerais opacos, allanita, zirc?o e apatita s?o os acess?rios. Contudo, os trabalhos de cartografia geol?gica tamb?m identificaram na regi?o a presen?a de outras unidades litoestratigr?ficas, descritas como gnaisses e migmatitos indiferenciados com lentes de anfibolitos relacionados ao Complexo Caic? (Paleoproterozoica) e rochas metassedimentares do Grupo Serid? (Neoproterozoico) compostos por paragnaisses com lentes de calciossilic?ticas, muscovita quartzitos e biotita xistos (respectivamente forma??es Jucurutu, Equador e Serid?), os quais s?o as encaixantes para as rochas do PGSR. Ainda foram identificados diques de leucomicrogranito e de pegmatitos, ambos relacionados ao final do magmatismo Ediacarano, bem como dep?sitos col?vio-eluviais e aluvionares relacionados ao Ne?geno e Quatern?rio, respectivamente. Dados litogeoqu?micos, na f?cies gran?tica do PGSR, evidenciam rochas bastante evolu?das (SiO2 69% a 75%), rica em ?lcalis (Na2O+K2O ? 8,0%), empobrecidas em MgO (? 0,45%), CaO (? 1,42%) e TiO2 (? 0,36%) e teores moderados de Fe2O3t (2,16 a 3,53%). Apresentam natureza transicional entre metaluminosa e peraluminosa (predom?nio do ?ltimo) e possuem afinidade subalcalina/monzon?tica (c?lcio-alcalina de alto K). Diagramas de Harker mostram correla??es negativas em Fe2O3t, MgO e CaO, indicando fracionamento de m?ficos e plagiocl?sio. O espectro de ETR mostra enriquecimento dos ETR leves com rela??o aos ETR pesados (LaN/YbN = 23,70 a 0,23), com anomalia negativa no Eu (Eu/Eu* = 0,70 a 0,23), sugerindo fracionamento ou acumula??o na fonte de feldspatos (plagiocl?sio). A integra??o dos dados permite correlacionar ?s rochas do PGSR ?quelas referidas na literatura como Su?te C?lcio-Alcalina de Alto K Equigranular. Considera??es sobre as condi??es de cristaliza??o para as rochas do PGSR foram obtidas a partir da integra??o de dados petrogr?ficos e litogeoqu?micos, os quais indicaram atua??o de condi??es moderadas a elevadas de ?O2 (parag?nese mineral titanita + magnetita + quartzo), magma progenitor saturado em H2O (cristaliza??o precoce das biotitas), atua??o de processos tardi-magm?ticos de fluidos ricos em ?CO2, H2O e O2 causando altera??es em parte da assembleia mineral (carbonata??o e saussuritiza??o dos plagiocl?sio, cloritiza??o das biotitas e esfenitiza??o dos opacos). Condi??es de termobarom?tricas foram estimadas com base em par?metros geoqu?micos (Zr e P2O5), bem como por minerais normativos CIPW, com resultados mostrando temperatura m?nima de liquidus da ordem de 800?C e temperatura de solidus da ordem de 700?C. As press?es final/m?nima de cristaliza??o sugerem ser da ordem de 3 a 5 Kbar. A presen?a de minerais zonados (plagiocl?sio e allanita) associadas a dados litogeoqu?micos diagramas bi-log para Rb vs Ba e Rb vs Sr sugerem a atua??o da cristaliza??o fracionada como processo dominante na evolu??o magm?tica do PGSR. Estudos geocronol?gicos U-Pb e isot?picos Sm-Nd indicam, respectivamente, que o biotita monzogranito possui idade de cristaliza??o de 557?13 Ma, com idade modelo TDM de 2,36 Ga, tendo valor de eNd para a idade de cristaliza??o de -20,10, permitindo inferir fonte crustal paleoproterozoica para o magma. / The ediacaran plutonic activity related to the Brasilian/Pan-African orogeny is one of
the most important geological features in the Borborema Province, represented along its
extension by numerous batholiths, stocks, and dikes.The object of this study, the Serra Rajada Granitic Pluton (SRGP), located in the central portion of the Piranhas-Serid? River Domain is an example of this activity. This pluton has been the subject of cartographic, petrographic, geochronological and
lithogeochemical studies and its rocks were characterized by two facies. First, the granitic
facies were described as monzogranites consisting of K-feldspar, plagioclase (oligoclase -
An23-24%), quartz and biotite (main mafic) and opaque minerals such as titanite, allanite,
apatite, and zircon as accessories. Alteration minerals are chlorite, white mica and
carbonate. Second, the dioritic facies consist of rocks formed by quartz diorite containing
plagioclase (dominant mineral phase), quartz and K-feldspar. Biotite and amphibole are the
dominant mafic minerals; and titanite, opaque minerals, allanite, zircon and apatite are the
accessories. However, previous geological mapping work in the region also identified the
presence of other lithostratigraphic units. These were described as gneisses and migmatites
with undifferentiated amphibolite lenses related to the Caic? Complex (Paleoproterozoic)
and metasedimentary rocks of the Serid? Group (Neoproterozoic) composed of paragneiss
with calc-silicate lenses, muscovite quartzite and biotite schist (respectively, the Jucurutu
formations, Equador and Serid?), the host rocks for the SRGP rocks. Leucomicrogranite and
pegmatite dikes have also been identified, both related to the end of the Ediacaran
magmatism and colluvial- eluvial and alluvial deposits related to Neogene and Quaternary,
respectively. Lithogeochemical data on the SRGP granite facies, highlighted quite evolved rocks
(SiO2 69% to 75%), rich in alkalis (Na2O+K2O ? 8.0%), depleted of MgO (? 0.45%), CaO
(? 1.42%) and TiO2 (? 0.36%) and moderate levels of Fe2O3t (2.16 to 3.53%). They display
transitional nature between metaluminous and peraluminous (predominance of the latter) with sub-alkaline/monzonitic (High K calcium-alkali) affinity. Harker diagrams show negative correlations for Fe2O3t, MgO, and CaO, indicating mafic and plagioclase fractionation. REE spectrum shows enrichment of LREE relative to heavy REE (LaN/YbN = 23.70 to 10.13), with negative anomaly in the Eu (Eu/Eu* = 0.70 to 0.23), suggesting fractionation or accumulation in the feldspars source (plagioclase). Data integration allows
to correlate the SRGP rocks with those described as Calcium-Alkaline Suite of equigranular High K.
The crystallization conditions of the SRGP rocks were determined from the integration of petrographic and lithogeochemical data. These data indicated intermediate to high conditions of ?O2 (mineral paragenesis titanite + magnetite + quartz), parent magma saturated in H2O (early biotite crystallization), tardi-magmatic processes of fluids rich in ?CO2, H2O and O2 causing part of the mineral assembly to change (plagioclase carbonation and saussuritization, biotite chloritization and opaques Sphenitization). Thermobarometrical
conditions were estimated based on geochemical parameters (Zr and P2O5) and CIPW normative minerals, with results showing the liquidus minimum temperature of about800?C and the solidus temperature of approximately 700?C. The final/minimum crystallization pressure are suggested to be between 3 and 5 Kbar. The presence of zoned minerals (plagioclase and allanite) associated with lithogeochemical data in bi-log diagrams for Rb vs. Ba and Rb vs. Sr suggest the role of fractional crystallization as the dominant
process in the magmatic evolution of SRGP. U-Pb Geochronological and Sm-Nd isotope studies indicated, respectively, the crystallization age of biotite monzogranite as 557 ? 13 Ma, with TDM model age of 2.36 Ga,
and ?Nd value of -20.10 to the crystallization age, allowing to infer paleoproterozoic crustal
source for the magma.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/21054 |
| Date | 23 April 2015 |
| Creators | Costa, Alan Pereira da |
| Contributors | 90459261487, Vilalva, Frederico Castro Jobim, 22140632850, Medeiros, Vladimir Cruz de, 28943180497, Nascimento, Marcos Antonio Leite do |
| Publisher | Universidade Federal do Rio Grande do Norte, PROGRAMA DE P?S-GRADUA??O EM GEODIN?MICA E GEOF?SICA, UFRN, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| 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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