The Response of the Earth to the Terminal Cataclysm

地球对末日灾难的反应

• 批准号: NE/J009024/1
• 负责人: Timothy Elliott
• 金额: $ 43.13万
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2013
• 资助国家: 英国
• 起止时间: 2013 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FJ009024%2F1
• 关键词: Response; Earth; Terminal; Cataclysm

The Earth grew via a series of impacts of smaller planets. The last major event saw a Mars-sized object hit the ~90% complete Earth. This impact involved sufficient energy to launch enough material into orbit to form the moon and melt the remaining Earth. If not before, this global melting event allowed the excess melt in the Earth to sink to the centre and form the core. This finished the main stage of construction but some 600 million years afterwards, a series of smaller, but not insubstantial impacts hit the Earth. This has been dubbed the Terminal Cataclysm and was originally recognised from the clustering of cratering ages on the moon at 3.9 billion years before present. Although less physically tangible, the influence on the Earth has been profound, at least from a resources perspective. Precious metals such as gold and platinum have an extremely high preference for residing in a metallic melt relative to silicate melt or crystal phases (silicate minerals comprise the outer layers of the Earth). Metallic melts than sank to produce the core, thus carried with them the vast majority of the Earth's initial inventory of Au and Pt. The Au and Pt that is currently accessible to humanity arrived with the Terminal Cataclysm, after core formation had locked away the original hoard. Since the Terminal Cataclym did not trigger further core formation, this so-called Late Veneer remained within the outer, silicate portion of the Earth. The precious metals from the late veneer are now well distributed throughout the Earth and this project will follow this redistribution from the Terminal Cataclysm. In doing so we will learn about the way in which the mantle (convecting, silicate portion of the Earth) behaves in the first half of Earth History. We also think that the Terminal Cataclysm may have triggered the onset of the modern form of convection we currently see as plate tectonics. We will investigate this idea by seeing if other ancient chemical signatures were homogenised at the same time as the Late Veneer. A positive result would suggest a link between the two processes and implicate the Terminal Cataclysm in starting this process.The method by which this work will be done is by high precision measurements of the isotope ratios of some of the so-called siderophile elements, namely W (as founded in old-style light bulbs and cutting tools) and Mo (used as an industrial lubricant). The isotope ratios of the meteorite material delivered by in the late veneer has different isotope ratios to the Earth before the Terminal Cataclysm. The differences are small but our new techniques have suitable precision to detect these. The strength of using isotope ratios to trace this process is that they are essentially changed only by mixing and little by other geological processes. By examining the isotope ratios of Mo and W in a sequence of increasingly young rocks, we hope to trace the mixing of the late veneer with the rest of the mantle.

地球通过一系列较小行星的影响生长。最后一个重大事件看到火星大小的物体击中了〜90％的完整地球。这种影响涉及足够的能量将足够的材料发射到轨道上以形成月球并融化剩余的地球。如果不是以前，这个全球熔化事件使地球中的多余熔体陷入了中心并形成核心。这完成了建设的主要阶段，但大约6亿年，一系列较小但没有造成的影响袭击了地球。这被称为末端大灾难，最初是从月球上的碎屑年龄的聚类中被认可的。尽管身体上的切实少，但至少从资源的角度来看，对地球的影响是深远的。贵金属（例如金和铂）具有极高的偏好，可居住在金属熔体中，相对于硅酸盐熔体或晶体相（硅酸盐矿物质包含地球的外层）。金属融化比沉没以产生核心，因此与他们一起携带的绝大多数AU和PT库存。在核心形成锁定了原始ho积后，目前可通往人类的AU和PT随着终端灾难而到达。由于末端灾难没有触发进一步的核心形成，因此这种所谓的晚贴面留在地球外部的硅酸盐部分中。现在已故饰面的贵金属现在在整个地球上分布得很好，该项目将遵循末端灾难的重新分配。通过这样做，我们将了解地球（对流，硅酸盐的一部分）在地球历史上半段的行为的方式。我们还认为，末端灾难可能触发了我们目前将其视为板块构造的现代对流形式的开始。我们将通过查看其他古老的化学特征是否与已故饰面同时匀浆来调查这个想法。一个积极的结果将暗示这两个过程之间的联系，并牵涉到末端灾难的开始过程中。通过对某些所谓的Siderophile元素的同位素比率进行高精度测量，即以旧式的灯泡和削减工具和MO（使用属于工业型的工业型）。在晚期贴面中传递的陨石材料的同位素比具有不同的同位素比在末端灾难之前的地球比。差异很小，但我们的新技术具有合适的精度来检测这些精度。使用同位素比跟踪此过程的强度是，仅通过混合而几乎没有其他地质过程来改变它们。通过以一系列越来越年轻的岩石来检查MO和W的同位素比，我们希望追踪已故贴面与其他地幔的混合。

项目成果

Tracing subducted black shales in the Lesser Antilles arc using molybdenum isotope ratios

• DOI: 10.1130/g38344.1
• 发表时间: 2016-12
• 期刊: Geology
• 影响因子: 5.8
• 作者: H. Freymuth;T. Elliott;M. V. Soest;S. Skora

Tungsten isotope composition of the Acasta Gneiss Complex

• DOI: 10.1016/j.epsl.2015.02.040
• 发表时间: 2015-06
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: M. Willbold;S. Mojzsis;Hart Chen;T. Elliott

Molybdenum isotope evidence for subduction-modified, recycled mafic oceanic crust in the mantle sources of ocean island basalts from La Palma and Hawaii

• DOI: 10.1016/j.epsl.2023.118399
• 发表时间: 2023-11
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: M. Willbold;Tim Elliott

Uranium isotope fractionation during slab dehydration beneath the Izu arc

• DOI: 10.1016/j.epsl.2019.07.006
• 发表时间: 2019-09-15
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Freymuth, Heye;Andersen, Morten B.;Elliott, Tim
• 通讯作者: Elliott, Tim

Molybdenum mobility and isotopic fractionation during subduction at the Mariana arc

• DOI: 10.1016/j.epsl.2015.10.006
• 发表时间: 2015-12-15
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Freymuth, Heye;Vils, Flurin;Elliott, Tim
• 通讯作者: Elliott, Tim