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.

地球是通过一系列较小行星的撞击而成长的。在上一次重大事件中，一个火星大小的物体撞击了地球约 90% 的面积。这次撞击需要足够的能量来将足够的物质发射到轨道上以形成月球并融化剩余的地球。如果不是以前的话，这次全球融化事件使地球中多余的融化物沉入中心并形成地核。这完成了主要的建造阶段，但大约六亿年后，一系列较小但并非无关紧要的撞击袭击了地球。这被称为“末期大灾变”，最初是通过 39 亿年前月球上的陨石坑年龄聚集而被认识到的。虽然物理上不太明显，但它对地球的影响是深远的，至少从资源的角度来看是这样。相对于硅酸盐熔体或晶相（硅酸盐矿物构成地球的外层），金和铂等贵金属更倾向于存在于金属熔体中。金属熔化后下沉形成地核，从而携带了地球初始库存的绝大多数金和铂。在核心形成锁定了最初的宝藏之后，人类目前可以获得的金和铂随着末日大灾变到达。由于末期大灾变并没有引发进一步的地核形成，这种所谓的晚饰面仍保留在地球外部的硅酸盐部分内。来自晚期单板的贵金属现已广泛分布在整个地球上，该项目将遵循末期大灾变的重新分配。通过这样做，我们将了解地幔（地球的对流硅酸盐部分）在地球历史上半段的行为方式。我们还认为，末期大灾变可能引发了我们目前视为板块构造的现代对流形式的开始。我们将通过观察其他古代化学特征是否与晚单板同时同质化来研究这个想法。积极的结果表明这两个过程之间存在联系，并暗示末期大灾变启动了这一过程。完成这项工作的方法是对一些所谓的亲铁元素的同位素比率进行高精度测量，即W（在老式灯泡和切削工具中发现）和Mo（用作工业润滑剂）。晚期单层所传送的陨石物质的同位素比与末期大灾变之前的地球有不同的同位素比。差异很小，但我们的新技术具有合适的精度来检测这些差异。使用同位素比率来追踪这一过程的优势在于，它们本质上仅通过混合而改变，而几乎不受其他地质过程的影响。通过检查一系列日益年轻的岩石中钼和钨的同位素比率，我们希望追踪晚期单板与地幔其余部分的混合。

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

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

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

High-Precision Mass-Dependent Molybdenum Isotope Variations in Magmatic Rocks Determined by Double-Spike MC-ICP-MS

双尖峰 MC-ICP-MS 测定岩浆岩中与质量相关的高精度钼同位素变化

• DOI: 10.1111/ggr.12109
• 发表时间: 2016
• 期刊: Geostandards and Geoanalytical Research
• 影响因子: 3.8
• 作者: Willbold M

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