Determination of Lu and Hf Mass Fractions and 176Hf/177Hf Ratios in Mafic-Ultramafic Rock Reference Materials by Multi-Collector Inductively Coupled Plasma-Mass Spectrometry

Abstract

Reported data for Lu, Hf mass fractions and ¹⁷⁶Hf/¹⁷⁷Hf isotopic ratios of mafic-ultramafic rock reference materials (RMs) are rare at present, hampering the comparison of data quality between difference laboratories. Herein, we measured the Lu and Hf mass fractions and the ¹⁷⁶Hf/¹⁷⁷Hf isotopic ratios of ten mafic-ultramafic rock RMs, including OKUM (komatiite), WPR-1 (serpentinised peridotite), NIM-N (norite), NIM-P (pyroxenite), UB-N (serpentinised peridotite), JP-1 (peridotite), NIM-D (dunite), MUH-1 (serpentinised harzburgite), HARZ01 (harzburgite), DTS-2b (dunite), which contain extremely low amounts of Lu and Hf (Lu, 2–150 ng g⁻¹; Hf, 5–500 ng g⁻¹). All measurements were conducted on a Neptune Plus multi-collector inductively coupled plasma-mass spectrometer employing an Aridus II desolvator inlet system and Jet sample/X skimmer cone configuration. The following RMs, OKUM, WPR-1, UB-N, JP-1, NIM-D, HARZ01 and DTS-2b, have ¹⁷⁶Hf/¹⁷⁷Hf precision of less than 60 ppm (2s) at test portions of 0.06 to 0.3 g, and are good ultramafic RMs for Lu-Hf systems. In contrast, significant Hf mass fraction and isotopic variability were observed in NIM-N, NIM-P and MUH-1 at test portion masses of 0.1 to 0.3 g. Collectively, our study provides a new database that can be used by the geochemical community for evaluating the Lu-Hf system of mafic-ultramafic rocks.