Study on the chemical state of the Earth's deep interior based on chemical and isotopic compositions of kimberlites and mantle materials

在这项研究中，我们旨在通过分析金伯利岩和各种与地幔有关的物质来揭示地球深部的化学状态，并检验一些关于地球内部化学结构的模型。为了采集原地金伯利岩，我们在中国和巴西进行了取样，但发现它们发生了很大的变化。我们可以了解到，新鲜的金伯利岩可能只在金伯利岩浆侵入像岩床这样的深度的有限地方才能找到。通过对来自格陵兰岛西部的新鲜金伯利岩中惰性气体的分析，我们发现它们的岩浆来源与洋岛玄武岩相似，可能来自下地幔，具有较高的^3He/^4He比值。由于金伯利岩富含挥发性元素，并且相对于球粒陨石表现出完整的铂族元素模式，因此可以推断下地幔可能有较少的脱气作用和更多的…还原作用与上地幔相比，它更具状态。另一方面，我们观察到远东俄罗斯地幔包体中的~3He/~4He比值低于空气中的~3He/~4He比值，暗示了该地区俯冲板块对地幔的影响。对于来自印度洋地区的下地壳和上地幔包体，我们观察到与MORBs相似的^3He/^4He比值和受空气影响的^&lt；40&gt；Ar/^&lt；36&gt；Ar。此外，我们还揭示了留尼汪岛地区小于1 Ma的毛里求斯玄武岩具有比老玄武岩更接近MORB值的锶、钕、铅同位素比值。这可以用MORB型上地幔物质对岩浆的热柱作用随时间的增加来解释。从夏威夷群岛周围洋底采集的碱性玄武岩中的稀有气体同位素中也可以观察到这种趋势，这表明上地幔物质可能受到洋岛玄武岩的影响。较少

In this study, we aimed to reveal the chemical state of the Earth's deep interior by analyzing kimberlites and various mantle-related materials and examine some models on the chemical structure of the Earth's interior. To collect in-situ kimberlites, we performed sampling in China and Brazil, but found them to have been much altered. We could get a knowledge that fresh kimberlites might have been only found in a limited place where kimberlite magmas were intruded at a depth like sills. By analyzing noble gases in fresh kimberlites from West Greenland, which we had got from foreign investigators, we have revealed that their magma sources are similar to those of ocean-island basalts and probably derived from the lower mantle based on their high ^3He/^4He ratios. Since kimberlites are enriched in volatile elements and show unfractionated platinum-group element patterns relative to those of chondrites, it can be inferred that the lower mantle might have been less degassed and more reduced … More state compared to the upper mantle. However, we could not identify the difference in tungsten isotope ratios between kimberlites and mantle-related materials of the upper mantle origin.On the other hand, we observed ^3He/^4He ratios lower than that of the air in mantle xenoliths from Far Eastern Russia, which suggests the effect of subducted slabs to the mantle in that area. For xenoliths of lower crust and upper mantle origin from the Indian Ocean area, we observed ^3He/^4He ratios similar to those of MORBs and ^<40>Ar/^<36>Ar ratios affected by the air. Furthermore, we have revealed that basalts of less than 1 Ma from Mauritius Island, which belongs to the Reunion hotspot, show Sr, Nd and Pb isotope ratios which are closer to MORB values than those of older basalts. This can be explained by increasing of the effect of plume magmas by the upper mantle materials of MORB types with time. Such tendency can also be observed in noble gas isotopes in alkaline basalts taken from the ocean floor around the Hawaiian Islands and it suggests a possibility that upper mantle materials might have been affected by the ocean-island basalts. Less