人工合成锆石Lu-Hf同位素标样方法研究

A preliminary study of the method for synthetic zircon Lu-Hf isotopic standard

研究了人工合成锆石并加入微量元素的实验方法和条件。人工合成锆石是以氧化锆和硅酸锂为原料,以钼酸锂和氧化钼为助熔剂,并加入其他元素如Hf、Lu、Yb、U、Th、Pb等元素,充分混匀后转入带盖铂金坩埚中,在高温马弗炉中连续加热生长形成锆石晶体。利用激光剥蚀系统与电感耦合等离子体质谱技术分析了合成锆石晶体中微量元素含量和Lu-Hf同位素组成,结果表明合成锆石晶体中Lu、Yb、U、Th、Pb等微量元素含量不均一,而Hf的含量和Lu-Hf同位素组成有很好的均一性。

This paper studies the experimental conditions,composition,trace element content and Lu-Hf isotopic ratios in synthetic zircons.The authors used zirconia and lithium silicate as raw material and lithium molybdate and molybdenum oxide as flux,added such elements as Hf,Lu,Yb,U,Th,and Pb,and then transferred to the platinum crucible with lid after full mixing.In the high-temperature muffle furnace,they were heated at 950℃ continuously for growth of zircon crystals.The synthetic zircon is a good tetragonal crystal and has the same Raman spectra as the standard type of zircon crystals.Laser ablation system with inductively coupled plasma mass spectrometry（LA-ICP-MS） was used to measure the content of trace elements in synthetic zircon,and Lu-Hf isotopic ratios were determined by LA-MC-ICPMS.The results show that values of U,Th,Pb and some other trace elements vary remarkably from one crystal to another and also from core to rim in one crystal.In contrast,Lu-Hf isotope ratios have very good homogeneity;the determined 176Hf/177Hf mean values for the zircon crystal are in agreement with each other in 2σ error.The synthetic zircon is expected to be a new zircon Lu-Hf isotopic standard sample and may be helpful to developing improved laboratory protocols for accurate in situ Lu-Hf isotopic measurement of natural zircon.The result of this study suggests that synthetic minerals may prove useful as in situ method development tools and can provide thinking and means for the production of other synthetic minerals as isotopic reference materials for in situ isotopic studies.