Variation in the analytical figure of merit for in situ Hf isotopic measurements by LA-MC-ICPMS in zircon standards at variable spatial resolutions

摘要

Lu-Hf isotopic systematics is a powerful tool and gained importance as a geochemical tracer in geosciences. A multi-collector inductively coupled plasma mass spectrometer coupled with a laser ablation system has been used to perform zircon hafnium (Hf) isotopic analysis, and protocol is established for measurement of Hf isotopes. Toward this, two zircon standards, Z91500 and Plesovice, have been used for Hf isotopic measurements at four different spot sizes (50, 40, 25, and 20 mu m). The isotopic data for >= 25 mu m have an excellent agreement with published data, but for 20 mu m, the results are erroneous and irrelevant to geological application. It has been observed that Hf beam intensity has a linear relation to the volume of the target (RM) ablated. Hf-178/Hf-177 ratio and eHf for both standards are comparable with the published recommended values. The present study indicates that Lu-176/Hf-177 ratio for Z91500 is more homogeneous than Plesovice zircon. The Hf-176/Hf-177 isotopic ratio for 50 and 25 mu m shows an excellent agreement with the previously reported data. However, for 40-mu m spot size, a slightly higher but negative offset of -123 and -105 ppm in Hf-176/Hf-177 ratio have been observed for Plesovice and 91500, respectively.