Accurate Determination of Zr Isotopic Ratio in Zircons by Femtosecond Laser Ablation MC-ICP-MS with “Wet” Plasma Technique

Abstract

This work evaluates the use of femtosecond laser ablation multiple collector inductively coupled plasma mass spectrometry (fs-LA-MC-ICP-MS) for Zr isotopic analysis in zircons. The mass fractionation caused by instrumental mass discrimination was corrected by a combination of internal correction using Sr as an internal standard (coming from a NIST SRM 987 standard solution) and external correction using a matrix-matched standard. Several important instrument parameters were investigated, such as the effect of the addition of N2 and “wet” plasma condition, the mass fractionation behaviors between Zr isotopes and Sr isotopes, the position effect in laser ablation cell and the effect of laser ablation parameters (laser spot size and energy density). The Zr isotope compositions of seven zircons (GJ-1, 91500, Plešovice, Rak-17, Paki, Aus and Mala) were determined by the developed fs-LA-MC-ICP-MS and thermal ionization mass spectrometry (TIMS). Our fs-LA-MC-ICP-MS results for Zr isotope compositions agreed with TIMS analyses within analytical uncertainties, indicating the presented method is a suitable tool to resolve isotopic zoning in natural zircons. The results also suggest that GJ-1, 91500, Plešovice, Paki, Aus and Mala had the homogenous Zr isotope composition and could be considered as the potential candidates for the Zr isotope analysis in zircons, except Rak-17 which presented the large Zr isotope variation.

Zr isotopes reveal long storage timescales of Archean magmas

“…and Plešovice yielded δ 94 Zr values of -0.03 ± 0.12‰ (2SD, n=174) and 0.14 ± 0.10‰ (2SD, n=152), respectively, consistent with the recommended δ 94 Zr values measured by LA-MC-ICPMS 15 and solution MC-ICPMS 18,20,22,23 . The second session used zircon PAKI (δ 94 Zr = 0.21 ± 0.08‰) 23 as the calibration standard and US, Penglai and Plešovice as monitor standards.…”

“…and Plešovice yielded δ 94 Zr values of -0.03 ± 0.12‰ (2SD, n=174) and 0.14 ± 0.10‰ (2SD, n=152), respectively, consistent with the recommended δ 94 Zr values measured by LA-MC-ICPMS 15 and solution MC-ICPMS 18,20,22,23 . The second session used zircon PAKI (δ 94 Zr = 0.21 ± 0.08‰) 23 as the calibration standard and US, Penglai and Plešovice as monitor standards. During this session, zircon US, Penglai and Plešovice gave δ 94 Zr values of 0.51 ± 0.12‰ (2SD, n=22), -0.11 ± 0.13‰ (2SD, n=10) and 0.17 and BIR-2G) were used for external calibration, and CGSG-1 glass was used as monitor standard.…”

“…Zircon is the most important carrier of Zr and zircon crystallization can result in significant variations of δ 94 Zr in residual melts [11][12][13] . However, the equilibrium zircon-melt Zr isotope fractionation is small (<0.1‰) at temperatures above 700 ℃ 29,30 and cannot explain the variations observed here and in previous studies [11][12][13][14][15][16][17][18][19][20][21][22][23][24] (Extended Fig. 4a).…”

“…Among the five stable isotopes of Zr, 94 Zr/ 90 Zr ratios are usually analyzed and reported as δ 94 Zr relative to IPGP-Zr standard (δ 94 Zr = 1000× [( 94 Zr/ 90 ZrSample/ 94 Zr/ 90 ZrIPGP)-1]) 11 . Recent studies report significant variations in the Zr isotope composition of different rocks (-0.13 to 0.63‰) and minerals (-4.24 to 1.01‰), though the mechanisms for these variations are still debated [11][12][13][14][15][16][17][18][19][20][21][22][23][24] .…”

In situ Ti isotopic analysis by femtosecond laser ablation MC-ICP-MS

“…, Mg isotopes in silicate samples, 39 Fe isotopes in Fe sulfides and oxides, 40 and Zr–Si isotopes in zircons. 41,42 Compared to ns-LA, particle size distribution produced by fs-LA is usually centered on d < 200 nm ( d is the aerodynamic diameter) and independent of the particle morphology, and no large size (>1 μm) bodies typical of ns-LA ablation melt or hard agglomeration products are observed. 43 Therefore, fs-LA produces much more consistent ablation for various materials, which largely minimizes the substrate and fluence dependence and thus improves analytical accuracy and precision.…”