地幔柱稀有气体同位素示踪研究的进展及其意义

    Progress in the research on noble gas isotope tracing of the mantle plume and its significance.

    • 摘要: 摘要:利用地幔柱、上地幔和地壳在稀有气体同位素组成方面的明显差异,国际上在对地幔柱进行示踪和判识方面已取得了良好的效果。地幔柱的3He/4He值大于8~8.5Ra(Ra=1.4×10-6),且高于上地幔和地壳值;地幔柱的20Ne/22Ne值大于等于10.8,与上地幔值接近,但地幔柱的21Ne/22Ne值低于上地幔值;地幔柱的40Ar/36Ar值一般明显低于上地幔值;地幔柱的129Xe/130Xe和136Xe/130Xe值普遍高于上地幔和地壳值,且高于上地幔值约10%以上。中国东部新生代地幔岩的3He/4He值总体在上地幔3He/4He端员值(8±1Ra)的上下变化,与地幔柱的3He/4He值差异较大。大火成岩省(LIP)的形成与深部地幔柱的活动有关,峨眉山玄武岩是中国目前唯一被学术界普遍认可的LIP。开展包括峨眉山玄武岩在内的有关地幔柱稀有气体同位素示踪方面的研究,对于深化中国地幔柱领域的研究和推动大陆动力学研究的进程具有重要意义。

       

      Abstract: Abstract: There is appreciable difference in noble gas isotopic composition among the mantle plume, upper mantle and crust. Using this feature, the mantle plume can be well traced and recognized. The 3He/4He ratios of the mantle plume are >8-8.5 Ra, higher than those of the upper mantle and crust. The 20Ne/22Ne ratios of the mantle plume are ≥10.8, close to those of the upper mantle, but the 21Ne/22Ne ratios of the mantle plume are lower than those of the upper mantle. The 40Ar/36Ar ratios of the mantle plume are generally lower than those of the upper mantle. The 129Xe/130Xe and 136Xe/130Xe ratios of the mantle plume are commonly higher than those of the upper mantle and crust, over 10% higher than those of the upper mantle. The 3He/4He ratios of Cenozoic pyrolites in eastern China generally fluctuate around the end-member values of 3He/4He of the upper mantle (8±1Ra) and differ from the 3He/4He ratios of mantle plume greatly. It is widely accepted that the upwelling of the mantle plume is closely associated with the formation of large igneous provinces (LIP). The Emeishan basalt is the only LIP in China recognized universally at present by the academic community. The study of noble gas isotope tracing of the mantle plume, including the study of the Emeishan basalt, has great significance for deepening the study of the mantle plume in China and advancing the process of continental dynamic research.

       

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