Characterization of xenotime from Datas (Brazil) as a potential reference material for in situ U-Pb geochronology

Vasconcelos, A. D. ; Goncalves, G. O. ; Lana, C. ; Buick, I. S. ; Kamo, S. L. ; Corfu, F. ; Scholz, R. ; Alkmim, A. ; Queiroga, G. ; Nalini Jr., H. A. (2018-07-16)

CITATION: Vasconcelos, A. D. et al. 2018. Characterization of xenotime from Datas (Brazil) as a potential reference material for in situ U-Pb geochronology. Geochemistry, Geophysics, Geosystems, 19:2262–2282, doi:10.1029/2017GC007412.

The original publication is available at https://agupubs.onlinelibrary.wiley.com

Article

This study investigates five megacrysts of xenotime (XN01, XN02, XN03, XN04, and XN05) as potential reference materials (RMs) for U‐Pb geochronology. These crystals belong to a 300 g xenotime assortment, collected from alluvial deposits in SE Brazil. Electron microprobe and Laser Ablation‐Inductively Coupled Plasma‐Mass Spectrometry (LA‐ICP‐MS) analyses show that the selected crystals are internally homogeneous for most rare earth element, (REE, except some light REE) but are relatively heterogeneous for U and Th. The xenotime REE patterns are consistent with an origin from hydrothermal quartz veins in the Datas area that cut greenschist‐facies metasediments and that locally contain other accessory phases such as rutile and monazite. High‐precision U‐Pb Isotope Dilution‐Thermal Ionization Mass Spectrometry (ID‐TIMS) analyses showed slight age heterogeneity for the XN01 crystal not observed in the XN02 sample. The two crystals have slightly different average 206Pb/238U ages of 513.4 ± 0.5 Ma (2 s) and 515.4 ± 0.2 Ma (2 s), respectively. In situ U‐Pb isotope data acquired via LA‐(Q,SF,MC)‐ICP‐MS are within the uncertainty of the ID‐TIMS data, showing homogeneity at the 1% precision of the laser ablation (and probably ion microprobe) technique. U‐Pb LA‐(MC, SF)‐ICP‐MS analyses, using XN01 as a primary RM, reproduced the ages of other established RMs within less than 1% deviation. Other Datas crystals (XN03‐05) also display a reproducibility in Pb/U dates better than 1% on LA‐ICP‐MS, making them good candidates for further testing by ID‐TIMS.

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