Geochemical investigation on core-mantle interactions

点击翻译按钮获取中文摘要

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.