Laser-ablation MC-ICP-MS lead isotope microanalysis down to 10 μm:Application to K-feldspar inclusions within zircon

• Published in: Journal of Analytical Atomic Spectrometry
• Main Authors: Delavault, Hélène, Dhuime, Bruno, Hawkesworth, Chris, Marschall, Horst R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2018
• Subjects: Dronning Maud Land; East Antarctica; Faraday; Antarc*; Antarctica
• Online Access: https://hdl.handle.net/1983/6f355a98-04c6-4aa4-aa6d-63c4cd992c40; https://research-information.bris.ac.uk/en/publications/6f355a98-04c6-4aa4-aa6d-63c4cd992c40; https://doi.org/10.1039/c7ja00276a; http://www.scopus.com/inward/record.url?scp=85041964409&partnerID=8YFLogxK

The geochemical information preserved in mineral inclusions within zircon provides new ways to decipher the evolution of the continental crust. We present a routine procedure to analyse Pb isotopes in K-feldspar minerals and mineral inclusions in zircon by LA-MC-ICP-MS, with a spot size down to 10 μm diameter. Natural K-feldspar grains from the Shap granite (north England) were selected for their homogenous Pb isotope composition to validate the method. The Faraday cups of the Thermo Scientific Neptune Plus MC-ICP-MS were used to collect the beams for spot sizes of 150 μm and 40 μm. The average 206 Pb/ 204 Pb ratios were respectively 18.255 ± 0.27% and 18.24 ± 1.3% (2 s.d.), and they agree within their analytical uncertainties. Ion counters (MIC) were used at 10 μm to allow better determination of the low intensity signal for Pb isotopes. The 206 Pb/ 204 Pb average ratio is 18.29 ± 1.3% (2 s.d.), which is within error of the average values at spot sizes of 150 μm and 40 μm. For a 10 μm spot size internal errors on individual measurements are typically better than 1.1% (2 s.e.). K-feldspar inclusions in zircons from a monzonite intrusion in Dronning Maud Land (East Antarctica), were analysed by MIC-LA-MC-ICP-MS (10 μm spot and ∼12 μm depth). The Pb isotope ratios are similar to those previously obtained by SIMS with a Cameca IMS 1270 (∼40 × 20 μm elliptic spot and ∼2 μm depth). These SIMS data are used to validate the robustness of MIC-LA-MC-ICP-MS measurements in minute mineral inclusions.