CHEN Juan^1,2, TANG Hong-feng¹, GUAN Jin³, WANG Ning¹

(1. Laboratory for High Temperature & High Pressure Study of the Earth's Interior, Institute of Geochemistry, CAS, Guiyang 550002, China;  
2. School of Chinese Academy of Sciences, Beijing 100049, China;
3. State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, CAS, Guiyang 550002, China) 

Abstract: By summarizing and contrasting previous analytical methods for Hf isotope, we chose a specific resin named Ln-Spec (100－150 mesh, H⁺) and MC-ICPMS to study four standard materials and nineteen bulk rock samples from East Junggar of Xinjiang Autonomous Region, China including eighteen granites and enclaves, and one basalt occurring in the Karamaili ophiolite suite. The ¹⁷⁶Hf/¹⁷⁷Hf ratios for international standard materials of BCR-1, BHVO-2, and W-2 are consistent with those reported in literatures within errors, demonstrating that the Hf chemical separation procedure for bulk rocks and analytical method for Hf isotope in solutions by mass spectrometry are reliable. In this paper, the ¹⁷⁶Hf/¹⁷⁷Hf ratio of 0.282547±07 (2s) for the Chinese granite standard material GRS-1 is reported for the first time. From the ¹⁷⁶Hf/¹⁷⁷Hf ratios, Lu and Hf concentrations measured by ICP-MS and formation age (300 Ma) of the granite and enclave samples, their ε_Hf(t) values can be obtained. These ε_Hf(t) values for bulk rock samples are generally consistent within errors with those for the zircons from the corresponding rock samples, suggesting that the initial Hf isotope compositions of bulk rocks with age of ~300 Ma are able to be calculated by using Lu and Hf concentrations measured with ICP-MS. The ε_Hf(t) for the basalt sample QS08-1 is identical with that of the zircon in plagiogranite occurring in the same ophiolite suite with this basalt, which provides a good example for studying Hf isotopic compositions of those rocks without or hard to separate zircons by using bulk rock ¹⁷⁶Hf/¹⁷⁷Hf ratios and Lu and Hf concentrations analyzed by using ICP-MS.

Key words: Hf isotope; MC-ICPMS; granite; East Junggar, Xinjiang