Method for Determining the Age of Igneous Rocks Using the Accessory Minerals

Larsen, Esper S.; Keevil, N. B.; Harrison, H. C.

doi:10.1130/0016-7606(1952)63[1045:mfdtao]2.0.co;2

Cited by 57 publications

(15 citation statements)

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“…Because of its common occurrence and its high affinity for many radionuclides (e.g., U, Th, REE, 90 Sr, 90 Y, etc. ), apatite has been used in geochronological and petrogenetic studies for decades (Larsen et al 1952;Altschuler et al 1958;Oosthuyzen and Burger 1973). However, little is known about the mechanism of incorporation and structure response of apatite to substituent actinides.…”

Section: Introductionmentioning

confidence: 99%

Crystal chemistry of Th in fluorapatite

Luo

Rakovan

Tang

et al. 2010

American Mineralogist

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Through the complementary use of single-crystal X-ray diffraction and X-ray absorption spectroscopy, we present in this paper the first direct results on the site occupancy of thorium in the fluorapatite structure and the structural distortion created by its substitution. Structure refinements based on single-crystal X-ray diffraction data from synthetic Th-doped fluorapatite indicates that Th substitutes almost exclusively in the M2 site. A single-crystal X-ray study of natural fluorapatite from Mineville, New York, also indicated that substituting heavy scatterers (including Th) are concentrated in the apatite M2 site, but definitive site assignments of specific elements were not possible. Extended X-ray absorption fine-structure spectroscopy (EXAFS) was used to probe the local structure of Th in the synthetic fluorapatite (single-crystal form) with a Th concentration of roughly 20 000 ppm, as well as Th in the natural Mineville fluorapatite (powder form) with a Th concentration of ~2000 ppm. The EXAFS fitting results also indicate that Th partitions into the M2 site and yield a ~0.05-0.08 Å decrease of average M2-O bond distances associated with local structure distortions that are not obtainable from single-crystal X-ray diffraction studies.

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Section: Introductionmentioning

confidence: 99%

Crystal chemistry of Th in fluorapatite

Luo

Rakovan

Tang

et al. 2010

American Mineralogist

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“…Havia, ainda, uma outra opção, que era um novo método denominado "chumbo-alfa" desenvolvido no U. S. Geological Survey. Devido à sua simplicidade, fácil instalação e baixo custo por amostra, o processo passou a ser intensivamente usado em vários países e teve uma sobrevida de aproximadamente 20 anos, desde que foi lançado por Larsen, Keevil e Harrison (1952). O método, com base em princípios da cristaloquímica, assume que, com certas precauções, todo o chumbo no zircão é praticamente de origem radiogênica.…”

Section: Geocronologiaunclassified

A geoquímica analítica em Minas Gerais: de Gorceix ao Geolab: a contribuição do ITI

Dutra¹

2002

Rem: Rev. Esc. Minas

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É apresentada a recuperação da memória histórica da Geoquímica Analítica em Minas Gerais desde os primeiros trabalhos de Henri Gorceix, em 1881. São descritos os trabalhos dos órgãos antigos, como o Serviço da Produção Mineral, a Secretaria da Agricultura do Estado de Minas Gerais e o Instituto de Tecnologia Industrial, órgãos cujos geoanalistas descreveram novos minerais, se especializaram na análise de tântalo-niobatos e minerais radioativos de nossos pegmatitos, fizeram cronogeologia, introduziram métodos espectroquímicos nos estudos de elementos-traços em rochas e deram suporte aos estudos da apatita e do pirocloro de Araxá. São realçados os trabalhos pioneiros do GEOLAB, o primeiro laboratório geoquímico de serviço no país.
Na historical account of the Analytical Geochemistry in Minas Gerais, Brazil, since the pioneering work of Henri Gorceix, in 1881, is presented. The analytical work, developed by the Serviço da Produção Mineral and the Instituto de Tecnologia Industrial (both of Minas Gerais State), for the study of new minerals colled in pegmatites, for trace elements investigations and for geochronological research is described. The analytical support given by ITI in the study of the apatite and pyrochlore deposits of Araxá is discussed and the pioneering work of GEOLAB, the first commercial geochemical laboratory of the country, is emphasized

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“…An age-determination on the Kunait zircon was carried out by the "lead-alpha" method proposed by Larsen et al (1952), which has been successfully applied to zircons by a number of workers in recent years (Larsen et al, 1953 ;Gottfried et al, 1956 ;Webber et al, 1956 ;Roques, 1956a). The assumptions made in the method are that all the lead in the zircon is radiogenic and that no loss or gain of radioactive elements or lead has occurred during the geological history of the mineral.…”

Section: Introductionmentioning

confidence: 99%

“…F is defined as :-Amount of uranium present Amount of uranium required to yield the same number of alpha-particles as the sample Larsen, Keevil, and Harrison (1952) give an average value of F = 0-71 for zircons. Using this value for the Kunait zircon, its age comes out as 497 million years.…”

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confidence: 99%