In situ determination of hafnium isotopes from rutile using LA-MC-ICP-MS

The hafnium isotopic analysis using laser ablation has been widely conducted on Hf-rich minerals (zircon/baddeleyite/calzirtite/eudialyte), however, little work has been reported on Hf-poor (<100 ppm) minerals. This work presents a detailed procedure of in situ hafnium isotopic analysis from rutile using laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). The rutile U-Pb dating reference material JDX shows homogeneous hafnium isotopic ratios, with ¹⁷⁶Hf/¹⁷⁷Hf=0.281795±0.000015 (2SD, n=33) and ¹⁷⁶Lu/¹⁷⁷Hf=0.000018±0.000004 (2SD, n=17) that suggest the possibility of using JDX as a new reference material hafnium isotopic measurement. We also measure hafnium isotopic compositions of other rutile U-Pb dating reference material (R10, Sugluk-4 and PCA-S207) and the ¹⁷⁶Hf/¹⁷⁷Hf values are similar to previously reported results, which confirms that we can acquire accurate and precise hafnium isotopic compositions using our developed analytical protocol. We analyzed hafnium isotopic compositions and U-Pb ages of rutile in high-temperature and ultrahigh-temperature granulites from various terrains of the Khondalite Belt from the North China Craton, combined with zircon results in the same area, suggesting that the metamorphic evolution history of the granulite is much more complicated than previously thought.