Determination of the Trace Element Composition and U–Pb Dating of Apatite by Inductively Coupled Plasma Laser Ablation Mass Spectrometry on a NexION 300S spectrometer with an NWR 213 Attachment

Abstract

The microelemental composition and isotope ratios Pb/U, Pb/Th, and Pb/Pb in apatite were determined by inductively coupled plasma and laser ablation mass spectrometry with on a NexION 300S spectrometer with an NWR 213 laser ablation (LA) attachment; the procedure for processing the experimental data was described. The optimal operation parameters of the mass spectrometer and the LA attachment were determined, also in determining the trace element composition and U/Pb dating from one crater of a size of 50 μm or more. In determining the microelemental composition of apatite, standard synthetic glasses NIST SRM-612, -610 were used; in measuring isotope ratios, reference samples (RS) were used—Durango, Mun Mad, and Mud Tank apatites, analyzed in laboratories in different countries. Using scanning electron microscopy data, the shape of laser ablation craters in RS apatite grains was analyzed; a significant heterogeneity of grains in the matrix and impurity elements was shown. The performance characteristics of the procedures for the measurement period 2021−2023 are presented. The repeatability of measuring the isotope ratios ²⁰⁶Pb/²³⁸U and ²⁰⁸Pb/²³²Th is 0.54 and 0.72, 7.5 and 14.3, 1.5 and 4.4% for Mun Mad, Durango, Mud Tank, respectively. Variations in the REE content of the reference samples (RSD) are 11−24, 5−13, 0.3−7% for Mun Mad, Durango, Mud Tank, respectively. The dating of the RS of apatite, within the limits of uncertainty, corresponds to those obtained in world laboratories. The methods were tested in the analysis of a number of apatite samples from Ural sites.