Zircon Hf-isotope analysis with an excimer laser, depth profiling, ablation of complex geometries, and concomitant age estimation

Abstract

This study examines the levels of precision and accuracy obtainable by laser ablation Hf-isotope analysis of zircons in real-world situations using a 193-nm ArF excimer laser coupled to a Nu Plasma MC-ICPMS. Three different reference materials (91500, BR266, and Temora-2) were studied with both solution MC-ICPMS (after Hf separation) and laser ablation. The long-term (9 months) levels of precision and accuracy obtained in these standards by laser ablation are ±90 and ca. 50 ppm (2 σ), respectively, closely approaching theoretical limits. The theoretical limiting precision can be expressed in terms of dependence on beam size and integration time. The quality of these data is attributed to a combination of high system sensitivity and a more robust correction for Yb interference than considered in previous studies of this kind. Novel solutions to the analysis of complex zircon growth morphologies have been tested including the ablation of non-standard geometries and depth profiling techniques, the latter tested by use of a composite zircon standard. Depth profiling appears to be viable as long as ablation pit aspect ratios remain below 2:1 (depth/width). Finally, the Nu Plasma zoom lens is employed to explore the possibility of simultaneous 207Pb– 206Pb age determination and Hf-isotope analysis.