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Noble Gas Partitioning Into The Earth's Outer Core? Ab Initio Calculations On Noble Gas Partitioning Between Silicate and Liquid Iron

惰性气体进入地球外核？

基本信息

批准号：
NE/S01134X/1
负责人：
Lidunka Vocadlo
金额：
$ 56.2万
依托单位：
University College London
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2019
资助国家：
英国
起止时间：
2019 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FS01134X%2F1
关键词：
Noble Gas Partitioning Into Earth

项目摘要

Rocks from some oceanic islands, such as Iceland and Hawaii, show an unusual geochemical signature with the ratio of isotopes of helium (3He/4He) being very high. Because 3He cannot be produced from radioactive decay, all the 3He must have originated from the accreting solar system. This suggests that the source of these rocks comes from material within a deep isolated primordial reservoir that has been trapped within the Earth throughout its history and has not been affected by subsequent mantle mixing and dynamics. For many years, scientists have been "searching" for these primordial reservoirs and have come up with a number of potential locations, such as regions close to the core-mantle boundary (Large Low Shear Velocity Provinces - LLSVPs, and Ultra Low Velocity Zones - ULVZs) and even isolated zones higher up in the mantle (Bridgmanite Enriched Ancient Mantle Structures - BEAMS). But all these suggestions have their problems. However, one deep reservoir that has received relatively little attention is the Earth's liquid outer core. To establish whether the outer core could, indeed, host noble gases, such as helium, requires knowledge of the partitioning of noble gases between the silicate mantle and the liquid iron alloy outer core. In this proposal we will calculate the necessary partition coefficients in order to determine whether or not the sources of primitive noble gases are consistent with an outer core reservoir. Our results will directly influence our understanding of the origin, scale and survival of mantle heterogeneities, and the intrinsic link to mantle convection and core- mantle exchange. These are some of the biggest issues for understanding the evolution of the Earth from its accretion to present day.

一些大洋岛屿的岩石，如冰岛和夏威夷，显示出不同寻常的地球化学特征，氦(3He/4He)的同位素比率非常高。因为3He不是从放射性衰变中产生的，所以所有的3He一定都来自于吸积太阳系。这表明，这些岩石的来源来自一个深而孤立的原始储集层中的物质，该储集层在整个历史上一直被困在地球内部，没有受到随后的地幔混合和动力学的影响。多年来，科学家们一直在寻找这些原始储集层，并提出了一些潜在的位置，例如靠近核-地幔边界的地区(大的低剪切速度省-LLSVP和超低速带-ULVZ)，甚至地幔更高的孤立地带(富含布里奇曼石的古地幔结构-梁)。但所有这些建议都有它们的问题。然而，一个相对较少受到关注的深层储集层是地球的液态外核。要确定外核是否确实可以容纳惰性气体，如氦，需要了解稀有气体在硅酸盐地幔和液态铁合金外核之间的分配情况。在这项提议中，我们将计算必要的分配系数，以确定原始惰性气体的来源是否与外核储集层一致。我们的结果将直接影响我们对地幔不均质性的起源、规模和存续的理解，以及对地幔对流和核幔交换的内在联系的理解。这些是理解地球从吸积到今天的演化的一些最大的问题。