Geochemical investigation on core-mantle interactions

我们调查了与地幔深处的地幔热柱有关的洋岛玄武岩样品中是否存在显示核-地幔相互作用的地球化学证据。我们使用了钨同位素示踪剂(182W/183W)，显示了不同的核和地幔物质的价值。我们建立了用阴离子色谱提纯钨的方法。该方法已用于萨摩亚、圣赫勒拿和大洋中脊玄武岩等洋岛玄武岩样品的分析。在分析前，我们考察了钨同位素分析的精度，发现182W/183W的分析精度可以达到0.3埃单位。测定了钨的丰度和同位素组成，对20多个样品进行了分析，未发现钨同位素异常。考虑到(1)玄武岩来源的钨丰度，估算了样品中钨的丰度，(2)钨同位素分析的精度，(3)核的钨丰度，(4)核的钨同位素组成，严格限制了岩芯物质对源地幔的贡献小于0.5%。此外，地幔的钨同位素组成是均匀的。在研究期间，我们发表了关于钨同位素分析的化学提纯方法的论文和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.