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.
Highlights
Zirconium is classified as a high field strength element (HFSE) in geochemistry, and has been widely used to trace the differentiation in silicate magmatic systems and to understand the co-evolution of the Earth’s mantle and crust (Tang and Li, 2021; Niu, 2004; Bau, 1996; Brenan et al, 1994; Woodhead et al, 1993)
The results show that when the laser spot size ranged from 15 to 30 μm, the signal intensity of 90Zr varied from 0.5 to 2 times, but δ Zr 94/90 GJ-1 in GJ-1 remained consistent within uncertainty
Combining the results of the two experiments, we demonstrate that changing laser ablation spot size, laser energy and the sig‐
Summary
Collection (no laser ablation) and the remaining 80 cycles for signal collection. The Sr solution (NIST SRM 987, 100 ng·g-1) was aspirated during the entire analytical procedure. Sr element was used as doping element to correct the Zr isotopic fractionation behavior. Standard-sample bracketing method (SSB) was used to solve the system devia‐ tion problem (Yang, 2009). All data reduction for the fs-LA-MC-ICP-MS analysis of Zr isotope ratios was conducted using “Iso-Compass” software (Zhang et al, 2020). 1.3.2 The TIMS analysis of Zr isotopes All of zircons investigated in this study were analyzed by TIMS with double spike method relatively to the IPGP-Zr stan‐ dard. These measurements were conducted at the State Key Laboratory of Geological Processes and Mineral Resources (GPMR), China University of Geosciences, Wuhan. Detailed descriptions of the TIMS procedure for Zr isotopic analyses are given in Feng et al (2020)
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