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Non-matrix-matched analysis of U-Th-Pb geochronology of bastnäsite by laser ablation inductively coupled plasma mass spectrometry.

Authors :
Luo, Tao
Zhao, He
Zhang, Wen
Guo, Jingliang
Zong, Keqing
Liu, Yongsheng
Zhang, Junfeng
Hu, Zhaochu
Source :
SCIENCE CHINA Earth Sciences. Apr2021, Vol. 64 Issue 4, p667-676. 10p.
Publication Year :
2021

Abstract

Bastnäsite is widespread in alkali granite, carbonatite and REE ore deposits. The U-Th-Pb ages of bastnäsite can constrain the mineralization age. Currently, the lack of suitable in situ analysis reference material is the major obstacle of bastnäsite U-Th-Pb geochronology. In this study, the matrix effects of U-Pb and Th-Pb age determination in bastnäsite using glass NIST 610 as the external calibration reference were evaluated with the 193-nm excimer LA-ICP-MS analysis in normal and additional gases laser ablation modes. The obtained U-Th-Pb ages of bastnäsite were approximately 7–11% lower than their reference values in the normal analytical mode (without additional gas). Fortunately, the determined systematic age biases in U-Th-Pb dating were significantly reduced (less than 1–2%) with the addition of water vapor within the ablation chamber. This reduction may be attributed to the observed significant suppression of 206Pb/238U and 208Pb/232Th downhole fractionation in both NIST 610 glass and bastnäsite by introducing a small quantity of water vapor in the ablation chamber. In addition, the obtained 206Pb/238U and 208Pb/232Th ages of bastnäsite K-9, LZ1384, and MAD809 showed great consistency with their corresponding recommended values. The obtained results show that accurate and precise U-Th-Pb ages of bastnäsite can be simultaneously obtained by using glass NIST 610 as the primary calibration standard in 193-nm LA-ICP-MS with the water vapor-assisted method. This simple and effective water vapor-assisted non-matrix-matched laser ablation method helps to promote the geological application of bastnäsite U-Th-Pb geochronology. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
16747313
Volume :
64
Issue :
4
Database :
Academic Search Index
Journal :
SCIENCE CHINA Earth Sciences
Publication Type :
Academic Journal
Accession number :
149631545
Full Text :
https://doi.org/10.1007/s11430-020-9715-1