IN-SITU HAFNIUM ISOTOPE RATIO ANALYSIS OF ZIRCON BY INDUCTIVELY-COUPLED PLASMA MULTIPLE COLLECTOR MASS-SPECTROMETRY

Hf isotopic data are reported for ten similar to 0.01-mm(2) subareas of a zircon crystal separated from the similar to 318-Ma diatreme of Elie Ness, Fife, Scotland. In situ analysis was achieved by ablation sampling with a Nd:YAG laser into an inductively-coupled plasma, with ions dispersed by a sector magnet and integrated in a 7-Faraday multicollector array. Despite large interferences from Yb (16% of mass 176) and Lu (0.4% of mass 176), 2 se precision of +/- 0.00004-0.00014 was achieved on Hf-176/Hf-177 in each subarea, each representing the analysis of similar to 10 ng of Hf. Overall reproducibility of +/- 0.00005 (2 sd) was obtained between the ten subareas, only a factor of 2-3 worse than that achieved by conventional TIMS Hf analysis based on 1-3 mu g Hf. Reproducibility of single-spot analyses is about a factor of 2 better than reported for ion microprobe studies of zircon Hf, with far less potential for inaccuracies caused by molecular isobaric interferences. The Elie Ness zircons are isotopically homogeneous in Hf, but the technique is expected to have great value for the understanding of multicomponent zircons from granitoids and sediments.