TARIM calcite: a potential reference material for laser ICPMS in situ calcite U–Pb dating

Abstract

Assisted by laser ablation (LA) inductively coupled plasma mass spectrometry (ICPMS) analytical techniques, calcite is now accepted as an important U–Pb dating mineral for application to various issues in geology. However, appropriate calcite reference materials with homogeneous composition and structure remain lacking due to limited research work on such reference materials. This study successfully identifies a new natural megacryst calcite reference material, TARIM, for in situ U–Pb isotope measurement by LA-ICPMS analysis. Electronic probe microanalysis (EPMA) shows TARIM to be a homogenous low-Mg calcite. LA-ICPMS trace elemental analyses and mapping results suggest that TARIM is relatively homogenous with U content (mean value = 0.48 μg g⁻¹) appropriate for U–Pb isotopic dating. U–Pb analysis using isotope dilution-thermal ionization mass spectrometry methods (ID-TIMS) yielded a lower intercept age of 208.5 ± 0.6 Ma (2S, mean squared weighted deviation (MSWD) = 1.04). A total of 515 LA-ICPMS U–Pb isotope analyses on random calcite pieces show consistent ages with a lower intercept age of 208.0 ± 0.4/3.2 Ma (2S, MSWD = 3.0), overlapping with the ID-TIMS age. We propose that TARIM calcite can be applied as a reference material for matrix-matched calibration or as a monitoring standard for calcite LA-ICPMS U–Pb dating.