Geochemical investigation on core-mantle interactions

我们研究了是否存在地球化学证据，表明核-幔相互作用的洋岛玄武岩样品有关的地幔柱从地幔深处。钨同位素示踪（182 W/183 W）显示了核幔物质的不同值。我们开发了一种利用阴离子色谱法提纯钨的方法。该方法已应用于萨摩亚、圣赫勒拿等大洋岛屿玄武岩和大洋中脊玄武岩样品的钨同位素分析，在此之前，我们考察了钨同位素分析的精度，发现182 W/183 W比值的分析精度可达0.3个单位。对20多个样品进行了钨丰度和同位素组成的测定，未发现钨同位素异常。考虑到（1）玄武岩源中钨的丰度，估计样品中钨的丰度，（2）钨同位素分析的精度，（3）岩心的钨丰度，（4）岩心的钨同位素组成，严格限制岩心物质对所分析样品的源地幔的贡献小于0.5%。此外，地幔钨同位素组成具有均一性，在研究期间，我们发表了一篇关于钨同位素分析的化学提纯方法的论文和一篇关于南太平洋样品的钨同位素组成的论文。

We investigated if there exists geochemical evidence which shows core-mantle interactions in the samples of ocean island basalts related to mantle plumes from deep in the mantle. We used tungsten isotope tracers (182W/183W) which shows different value between core and mantle materials. We developed tungsten purification method using anion-chromatography. The developed method has been applied to the samples of oceanic island basalts, from such as Samoa and St. Helena and Mid-Oceanic Ridge basalts.Before the analyses we investigated precision of tungsten isotope analyses and found that 182W/183W ratio can be analyzed with a precision of 0.3 epsilon unit. Tungsten abundances as well as isotopic composition were measured.Anlyses of more than twenty samples show no tungsten isotope anomaly. Considering (1) tungsten abundances in the source of the basaltic estimated tungsten abundances in the samples, (2) precision of tungsten isotopic analyses, (3) tungsten abundance of the core, and (4) tungsten isotopic composition of the core, put tight constraints on the contribution of core material into the source mantle of the analyzed samples was less than 0.5%. In addition, the Earth's mantle is homogeneous regarding tungsten isotopic compositions.During the study period, we published a paper on chemical purification method for tungsten isotopic analyses and a paper on the tungsten isotopic compositions of the samples from south Pacific samples.