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The Diamantina Monazite: A New Low-Th Reference Material for Microanalysis

Authors

Gonçalves,  Guilherme O.
External Organizations;

Lana,  Cristiano
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Scholz,  Ricardo
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Buick,  Ian S.
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Gerdes,  Axel
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Kamo,  Sandra L.
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Corfu,  Fernando
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Rubatto,  Daniela
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/persons/resource/michawi

Wiedenbeck,  Michael
3.1 Inorganic and Isotope Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Nalini,  Hermínio A.
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Oliveira,  Luiz Carlos A.
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Citation

Gonçalves, G. O., Lana, C., Scholz, R., Buick, I. S., Gerdes, A., Kamo, S. L., Corfu, F., Rubatto, D., Wiedenbeck, M., Nalini, H. A., Oliveira, L. C. A. (2018): The Diamantina Monazite: A New Low-Th Reference Material for Microanalysis. - Geostandards and Geoanalytical Research, 42, 1, 25-47.
https://doi.org/10.1111/ggr.12192


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_2657889
Abstract
Most 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 Espinhaço 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 εNd(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.