scholarly journals DESENVOLVIMENTO DO MÉTODO DE DATAÇÃO QUÍMICA U-Th-Pb DE MONAZITA POR MICROSSONDA ELETRÔNICA NA UFMG

2013 ◽  
Author(s):  
Alexandre de Oliveira Chaves ◽  
Elizabeth Kerpe de Oliveira ◽  
Luiz Rodrigues Armoa Garcia
Keyword(s):  
Electron Microprobe ◽  
Chemical Data ◽  
Common Lead ◽  
Icp Ms ◽  
Dating Method ◽  
Physics Department ◽  
Chemical Dating

O método de datação química U-Th-Pb (não-isotópica) de monazita por microssonda eletrônica vem sendo desenvolvido há pelomenos 20 anos e já tem o reconhecimento da comunidade geológica por apresentar resultados que se equivalem à geocronologia isotópicaU-Pb. Este mineral contém quantidades negligenciáveis de chumbo comum, guardando apenas Pb radiogênico proveniente do Th e U destemineral. O desenvolvimento deste método no Laboratório de Microanálises do Departamento de Física da Universidade Federal de MinasGerais mostra que os dados químicos de U, Th e Pb de cristais de monazita fornecidos por sua microssonda eletrônica produzem idadesnão-isotópicas para eles que se equiparam às idades isotópicas U-Pb produzidas pela técnica LA-ICP-MS. Grãos de monazita de placersmarinhos de Buena (RJ) isotopicamente datados pelo método U-Pb com idades entre 530 e 580 Ma foram quimicamente datadas na UFMGentre 505 e 580 Ma. Estes resultados são consideravelmente compatíveis e colocam o referido laboratório a disposição da comunidadegeocientífica para obtenção de idades de cristais de monazita.Palavras-Chave: MONAZITA, DATAÇÃO QUÍMICA, MICROSSONDA ELETRÔNICA, UFMG ABSTRACTDEVELOPMENT OF THE MONAZITE U-Th-Pb CHEMICAL DATING METHOD BY USING ELECTRON MICROPROBE AT UFMG. Themonazite U-Th-Pb chemical dating method (non-isotopic) by electron microprobe has been developed for about 20 years and has theacceptance of the geological community by presenting results that are equivalent to the isotope U-Pb geochronology. This mineral containsnegligible amounts of common lead, keeping only radiogenic Pb from the Th and U of this mineral. The development of this method in themicroanalysis laboratory of the Physics Department- UFMG shows that the monazite U, Th and Pb chemical data provided by itsmicroprobe produce non-isotopic ages for it that are similar to the U-Pb isotopic ages produced by LA-ICP-MS technique. Monazite grainsfrom marine placers of Buena (RJ) isotopically dated by method U-Pb between 530 and 580 Ma were chemically dated at UFMG between505 and 580 Ma. These results are consistent each other and put the laboratory available to the geoscience community as a tool inobtaining monazite ages.Keywords: MONAZITE, CHEMICAL DATING, ELECTRON MICROPROBE, UFMG

An Evaluation of Dating of Diagenetic Xenotime by Electron Microprobe.

2000 ◽  
Vol 6 (S2) ◽  
pp. 408-409 ◽  
Author(s):  
Brendan J. Griffin ◽  
Duncan Forbes ◽  
Neal J. McNaughton
Keyword(s):  
Electron Microprobe ◽  
Detrital Zircon ◽  
Microprobe Analysis ◽  
Electron Microprobe Analysis ◽  
Decay Rates ◽  
Wide Range ◽  
Isotopic Geochronology ◽  
Backscattered Electron ◽  
Dating Method ◽  
Chemical Dating

Xenotime is an igneous mineral commonly present in pegmatite and fractionated granite. Recent studies reveal that it also forms as a diagenetic mineral. Minute (0.1-5 μm) xenotime overgrowths typically crystallise on the surfaces of detrital zircon shortly after sedimentation, in a wide range of siliciclastic sedimentary units. For example, in backscattered electron (BSE) imaging using a scanning electron microscope (SEM), two minute, euhedral, pyramidal, xenotime overgrowths on an oscillatory-zoned detrital Ambergate zircon are evident (figure 1).Electron microprobe analysis (EMPA) geochronology is a chemical dating method that uses precisely measured concentrations of U, Th, and Pb, and the decay rates of U238, U235, and Th232, to calculate an age for a mineral. The EMPA dating method used in this study to date igneous xenotime and igneous-metamorphic monazite is the chemical isochron method (CHIME). EMPA geochronology is not a widely used technique because of the higher precision of isotopic geochronology.

An improved U–Pb age dating method for zircon and monazite using 200/266 nm femtosecond laser ablation and enhanced sensitivity multiple-Faraday collector inductively coupled plasma mass spectrometry

2015 ◽  
Vol 30 (2) ◽  
pp. 494-505 ◽  
Author(s):  
Jun-Ichi Kimura ◽  
Qing Chang ◽  
Keita Itano ◽  
Tsuyoshi Iizuka ◽  
Bogdan Stefanov Vaglarov ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Laser Ablation ◽  
Inductively Coupled Plasma ◽  
Femtosecond Laser Ablation ◽  
Age Dating ◽  
Inductively Coupled ◽  
Enhanced Sensitivity ◽  
Icp Ms ◽  
Plasma Mass Spectrometry ◽  
Dating Method

High precision U–Pb dating using multiple Faraday collectors has become available in LA-MC-ICP-MS.

Arsenopyrite and As-bearing pyrite from the Roudný deposit, Bohemian Massif

2004 ◽  
Vol 68 (1) ◽  
pp. 31-46 ◽  
Author(s):  
J. Zachariáš ◽  
J. Frýda ◽  
B. Paterová ◽  
M. Mihaljevič
Keyword(s):  
Laser Ablation ◽  
Fluid Inclusion ◽  
Electron Microprobe ◽  
Gold Deposits ◽  
Fluid Inclusion Data ◽  
The Core ◽  
Trace Element Chemistry ◽  
Mineral Phases ◽  
Icp Ms ◽  
Substitution Mechanism

AbstractThe major- and trace-element chemistry of pyrite and arsenopyrite from the mesothermal Roudný gold deposits was studied by electron microprobe and laser ablation ICP-MS techniques. In total, four generations of pyrite and two of arsenopyrite were distinguished. The pyrite is enriched in As through an Fe (AsxS1–x)2 substitution mechanism. The As-rich zones of pyrite-2 (up to 4.5 wt.% As) are also enriched in gold (up to 20 ppm), lead (commonly up to 220 ppm, exceptionally up to 1500 ppm) and antimony (commonly <600 ppm, rarely up to 1350 ppm). Positive correlation of As and Au in the studied pyrites is not coupled with an Fe deficiency, in contrast to Au-rich As-bearing pyrites in Carlintype gold deposits. The As-rich pyrite-2 coprecipitated with the Sb-rich (1 –4.2 wt.%) and Au-rich (40 –150 ppm) arsenopyrite-1. The younger arsenopyrite-2 is significantly less enriched in these elements (0 –70 ppm of Au).The chemical zonality of pyrites in the Roudný gold deposits reflects the chemical evolution of orebearing fluids that are not observed in any other mineral phases. The data available suggest relatively high activity of sulphur and low activities of arsenic and gold during crystallization of the older pyrite generation (pyrite-1). Later, after particular dissolution of pyrite-1, Au-rich As-bearing pyrite-2 and arsenopyrite precipitated. These facts suggest a marked increase in the arsenic and gold activities in ore-bearing fluids. The As-content of pyrite-2 decreases in an oscillatory manner from the core to the rim, reflecting changes in the As activity or/and in the P-T conditions. The As-bearing pyrites were formed at temperatures of at least 320–330°C, based on arsenopyrite thermometers and fluid inclusion data.

Quaternary plutonic magma activities in the southern Hachimantai geothermal area (Japan) inferred from zircon LA-ICP-MS U–Th–Pb dating method

2013 ◽  
Vol 265 ◽  
pp. 1-8 ◽  
Author(s):  
Hisatoshi Ito ◽  
Akihiro Tamura ◽  
Tomoaki Morishita ◽  
Shoji Arai ◽  
Fumiaki Arai ◽  
...  
Keyword(s):  
Geothermal Area ◽  
Icp Ms ◽  
Dating Method

Electron microprobe and LA-ICP-MS study of monazite hydrothermal alteration:

2000 ◽  
Vol 64 (19) ◽  
pp. 3283-3297 ◽  
Author(s):  
Franck Poitrasson ◽  
Simon Chenery ◽  
Thomas J Shepherd
Keyword(s):  
Hydrothermal Alteration ◽  
Electron Microprobe ◽  
Icp Ms

scholarly journals IDADE U-Th-Pb DA MONAZITA E CORONAS DE REAÇÃO FOSFATO-SILICATO DE METACHARNOENDERBITO NEOARQUEANO DO SUL DO CRÁTON SÃO FRANCISCO (MG)

2016 ◽  
Author(s):  
Daniel Andrade Miranda ◽  
Alexandre de Oliveira Chaves
Keyword(s):  
Electron Microprobe ◽  
Granulite Facies ◽  
Amphibolite Facies ◽  
Metamorphic Fluids ◽  
Phosphate Silicate ◽  
Chemical Dating

ResumoNa porção Sul do Cráton São Francisco (MG), a oeste da cidade de Bom Sucesso, ocorrem litotipos neoarqueanos metamorfizados que variam desde termos ultramáficos, gabro-noríticos, enderbíticos a charnockíticos, e graníticos. Proveniente desta associação, um metacharnoenderbito cristalizado e metamorfizado em fácies granulito por volta de 2700 Ma, guarda cristais de monazita com coronas de apatita, allanita e epidoto surgidas pela interação da monazita com fluidos metamórficos tardios contendo Ca, Fe, Si e Al. Através da microssonda eletrônica, as composições dos cristais de monazita foram determinadas e seus teores de U, Th e Pb permitiram a obtenção de uma idade química neoarqueana média de 2657 ± 36 Ma. Sugere-se que ela corresponda à idade do retrometamorfismo de fácies anfibolito do metacharnoenderbito desenvolvido durante o período tardi-colisional Neoarqueano do evento Rio das Velhas, momento durante o qual as coronas de reação fosfato-silicato teriam se desenvolvido contemporaneamente ao crescimento de anfibólio e biotita da referida rocha.Palavras Chave: monazita, datação química U-Th-Pb, coronas de reação fosfato/silicato, Neoarqueano, Cráton São Francisco.AbstractMONAZITE U-Th-Pb AGE AND PHOSPHATE-SILICATE REACTION CORONAS OF A NEOARCHEAN METACHARNOENDERBITE FROM SOUTHERN SAO FRANCISCO CRATON (MG). In the southern portion of the São Francisco Craton (MG), west of the Bom Sucesso city, neoarchean metamorphosed lithotypes outcrop, which include ultramafic bodies, gabbro-norites, enderbites to charnockites, and granites. From this association, a metacharnoenderbite crystallized and metamorphosed under granulite facies around 2700 Ma yielded monazite crystals with apatite, allanite and epidote coronas arising due to the interaction of monazite with metamorphic fluids containing Ca, Fe, Si and Al. By electron microprobe, an average chemical age of 2657 ± 36 Ma was obtained. It is suggested that it corresponds to the age of amphibolite facies retrometamorphism developed during the Neoarchean late-collisional period of the Rio das Velhas event, during which time the phosphate-silicate reaction coronas would have developed contemporarily to the growth of amphibole and biotite in such rock.Keywords: Monazite, U-Th-Pb chemical dating, phosphate/silicate reaction coronas, Neoarchean, São Francisco Craton.

scholarly journals De Karisimbi, Een Recente Vulkaan van Het Virungagebied (Rwanda, Zaire)

Afrika Focus ◽  
1986 ◽  
Vol 2 (1) ◽  
pp. 23-54
Author(s):  
Mark de Mulder
Keyword(s):  
Fractional Crystallization ◽  
Field Work ◽  
Geological Structure ◽  
Radiometric Dating ◽  
Chemical Data ◽  
Laboratory Studies ◽  
Crustal Rocks ◽  
Dating Method ◽  
Ultimate Purpose

Karisimbi, A Recent Volcano of the Virunga Area (Rwanda, Zaire) This paper deals with the geological structure and the petrologic evolution of Karisimbi, the highest volcano in the Virunga region. As this paper is intended to be understood by non-geologists, a brief review about the methods used by volcanologists, should make things clear for the reader. The field-work data enabled us to describe the morphology, structure and the evolution of Karisimbi. The results of the laboratory studies are summarized in the section petrography – petrochemistry, where some problems concerning nomenclature and interpretation of chemical data are discussed as well. Petrographical and petrochemical information leads us to the origin and the evolution of magmas, which is the ultimate purpose of every petrologist. In the case of Karisimbi, it is suggested that its petrologic evolution took place by simultaneous fractional crystallization and contamination by crustal rocks. Finally, the ages of some typical Karisimbi lavas have been determined by a radiometric dating method (K-Ar), bearing in mind that large errors on these ages are inevitable.

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