U-Pb dating by zircon dissolution method using chemical abrasion

Anais da Academia Brasileira de Ciências

Lucy Takehara²  Farid Chemale Júnior¹  Léo A. Hartmann¹  Ivo A. Dussin¹  Koji Kawashita¹ 

[1] ,CPRM Serviço Geológico do Brasil Brasília DF ,Brasil

关键词: chemical abrasion;    ID-TIMS;    LA-MC-ICPMS;    U-Pb dating;    zircon dissolution;    abrasão química;    ID-TIMS;    LA-MC-ICPMS;    datação U-Pb;    dissolução de zircão;   

DOI  :  10.1590/S0001-37652012000200011

来源: SciELO

【 摘 要 】

Chemical abrasion was carried out on zircons grains of the Temora II standard for U-Pb dating prior to analyses using in situ Laser Ablation-MultiCollector Ion Coupled Plasma Mass Spectrometer (LA-ICPMS) followed by the Isotope Dissolution Thermal Ionization Mass Spectrometer (ID-TIMS) method. The proposed methodology was herein applied in order to reduce primarily the effects of secondary Pb loss, the presence of common lead and/or silicate impurities. Nine Temora II zircon grains were analyzed by the laser ablation method yielding an age of 418.3±4.3 Ma. Zircon grains of a same population were separated for chemical abrasion before dissolution and mass spectrometry analyses. Six fractions of them were separated for isotope dissolution using 235U-205Pb mixed spike after we have checked and assured the laboratory conditions of low blank values for total Pb of less than 2 pg/g. The obtained U-Pb zircon age by the ID-TIMS method was 415.7±1.8 Ma (error 0.43 %) based on four successful determinations. The results are consistent with the published ages for the Temora diorite (Temora I – 416.75±1.3 Ma; Temora II – 416.78±0.33 Ma) and established as 416±0.33 Ma. The technique is thus recommended for high precision U-Pb zircon analyses (error < 1 %), mainly for high resolution stratigraphic studies of Phanerozoic sequences.

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