DEGEO - Departamento de Geologia
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8
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Item The Diamantina monazite : a new Low‐Th reference material for microanalysis.(2018) Gonçalves, Guilherme de Oliveira; Lana, Cristiano de Carvalho; Cipriano, Ricardo Augusto Scholz; Buick, Ian S.; Gerdes, Axel; Kamo, Sandra L.; Corfu, Fernando; Rubatto, Daniela; Wiedenbeck, Michael; Nalini Júnior, Hermínio Arias; Oliveira, Luiz Carlos Alves deMost monazite reference materials (RMs) for in situ U-Pb geochronology are rich in Th; however, many hydrothermal ore deposits contain monazite that is low in trace element contents, including Th, U and Pb. Because of potential problems with matrix effects and the lack of appropriate matrix-matched RMs, such variations can bias dating of hydrothermal deposits. In this paper, we describe a polycrystalline low-U and low-Th Diamantina monazite from the Espinhac o Range, SE Brazil. It has a U-Pb ID-TIMS weighted mean 207Pb*/235U ratio of 0.62913 ± 0.00079, 206Pb*/238U of 0.079861 ± 0.000088 and 207Pb*/206Pb* of 0.057130 ± 0.000031, yielding a weighted mean 206Pb*/238U date of 495.26 ± 0.54 Ma (95% c.l.). In situ dates acquired with different methods (LA-(Q, SF, MC)-ICP-MS and SIMS) are within uncertainty of the ID-TIMS data. U-Pb LA-(Q, MC)-ICP-MS runs, using Diamantina as a primary RM, reproduced the ages of other established RMs within < 1% deviation. The LA-MC-ICP-MS analyses yielded homogeneous Sm-Nd isotopic compositions (143Nd/144Nd = 0.511427 ± 23, 2s; 147Sm/144Nd = 0.1177 ± 13, 2s) and eNd(495 Ma) of -18.7 ± 0.5 (2s). SIMS oxygen isotope determinations showed measurement reproducibility better than ± 0.3‰ (2s), confirming Diamantina’s relative homogeneity at test portion masses below 1 ng.