This work presents a rigorous assessment of the accuracy and precision
with which (176)Hf/(177)Hf can be measured in rutile by laser ablation
(LA) MC-ICPMS. For rutile with >= 40 ppm Hf, we demonstrate that
(176)Hf/(177)Hf can be measured accurately and reproducibly with
adequate precision for application to petrological problems. We present
an analytical and data reduction protocol tailored to the specific
challenges of measuring Hf isotope ratios in this low-Hf mineral.
Precision and accuracy are optimised by interpolating between baselines
measured every similar to 10 analyses. For many rutiles, the advantages
of determining the Hf mass bias coefficient, beta(Hf), during analysis
are negated by the low precision with which it can be measured at low Hf
contents. Hf mass bias is therefore monitored by regular analysis of a
synthetic rutile doped with similar to 5000 ppm Hf (SR-2) to facilitate
an external mass bias correction. Because rutile contains negligible Yb,
the Yb mass bias coefficient beta(Yb) must be inferred from
beta(Yb)/beta(Hf) measured on zircon in the same session. To account for
a systematic instrument bias of 0.5-1 epsilon(Hf) units, rutile analyses
are normalised to SR-2, for which (176)Hf/(177)Hf has been determined by
solution MC-ICPMS. In situ (176)Hf/(177)Hf measurements for two natural
ruble samples with 40-50 ppm Hf are in excellent agreement with solution
MC-ICPMS values. Ti/Hf exerts no influence on the accuracy of
(176)Hf/(177)Hf measurements on our LA-MC-ICPMS, as illustrated by
indistinguishable (176)Hf/(177)Hf measurements for a series of synthetic
rutiles doped with varying amounts of Hf. Rutile and zircon from the
Duria mantle peridotite (Central Alps), which formed at different parts
of the P-T-time path, record contrasting Hf isotope signatures and
emphasise the complementary nature of Hf isotope analysis of rutile and
zircon. (C) 2010 Elsevier B.V. All rights reserved.