Quantifying the chemistry of sulfide in the core and its influence on the composition of the silicate Earth

地球和内太阳系岩石行星的化学成分传统上被认为与原始的“陨石”相同，是太阳系中最早形成的物质之一。然而，最近的研究表明，地球并不具有类似陨石的成分，而是在太阳系历史的早期失去了相当大的一部分（约10%）质量。已经流失的物质高度富集所谓的“不相容”元素（即那些具有大尺寸（离子半径）的元素，它们优先进入硅酸盐熔体），包括铀、钍和钾，这些物质一起通过放射性衰变产生了地球内部的大量热量。在现代硅酸盐地球中观察到的同位素特征表明，这些物质一定是在地球在其历史的头1亿年。在这段时间里，金属从成长中的地球中的硅酸盐中分离出来，在行星的中心形成了一个金属核，在上面留下了硅酸盐地幔，在表面留下了地壳。一些人认为，地球最早期的地壳由于与其他生长中的行星碰撞而被移除，导致了“不相容”的富含元素的物质的流失，但这使得地球没有了完整的产热元素。其他人认为这些元素可能储存在硅酸盐地幔深处的一个隐藏的水库中，但到目前为止还没有观察到这个水库的化学或热痕迹。此外，模型表明，在地幔底部高度集中的发热元素可能会阻止地球发电机（在液态外核中产生地球磁场）。每一种假说对地球的化学、动力学和热演化都有非常不同的影响，但每一种假说都提出了难以回避的问题。地震和实验工作的地震数据表明，地球的金属核主要由铁镍金属组成，但也包括“较轻”的元素，其中主要是硫化物。实验和同位素数据表明，硫是后来作为富硫金属或硫化物添加到核心的。通常情况下，“不相容的”预计不会被纳入铁镍金属，然而，值得注意的是，我们自己的初步实验数据表明，它们富含硫化物。与此同时，新的稳定同位素数据也与“不相容”的硫化物和随后的迁移到核心的合并。核心中的硫化物提供了一个不相容的元素富集储层，能够平衡硅酸盐地球的组成，为非南极地球提供了一个优雅的解决方案。本项目的总体目标是（1）通过模拟地核形成条件的高压实验，量化硫化物在地球生长和地核形成过程中的作用。(2)评估地核中硫化物对地球硅酸盐地幔成分的影响，以及（3）使用钕稳定同位素评估大陆形成和再循环的潜在影响。

The chemical composition of the Earth and rocky planets of the inner solar system is traditionally thought to be the same as primitive "chondritic" meteorites, amongst the earliest material formed in our solar system. Recent work, however, shows that the Earth does not have a chondrite-like composition, but instead appear to have lost a substantial part (some 10%) of its mass early in solar system history. The material that has been lost is highly enriched in so-called "incompatible" elements (that is, those elements with a large size (ionic radius) that preferentially go into silicate melts) including uranium, thorium and potassium, which together are responsible for generating much of Earth's internal heat through radioactive decay.The isotope signature observed in the modern silicate Earth indicates that this material must have been lost from Earth in the first 100 million years of its history. During this time metal separated from silicate in the growing Earth, forming a metallic core at the centre of the planet, leaving a silicate mantle above and crust at the surface. Some have argued that the loss of "incompatible" element rich material this was due to the removal of Earth's earliest crust through collisions with other growing planets, but this leaves the Earth without its full complement of heat-producing elements. Others have argued that these elements might be stored in a hidden reservoir deep in the silicate mantle, but so far no chemical or thermal trace of this reservoir has been observed. Moreover, models suggest that a high concentration of heat-producing elements at the base of the mantle may prohibit a functioning geodynamo (generation of the Earths magnetic field in the liquid outer core). Each of these hypotheses has very different implications for the chemical, dynamic and thermal evolution of Earth, but each poses problems that are difficult to circumvent. Seismic data from earthquakes and experimental work indicates that the Earths metallic core is principally composed of Fe-Ni metal, but also includes "lighter" elements, chief amongst which is sulphide. Experimental and isotope data suggest that sulphur was added late to the core either as a S-rich metal or as sulfide. Normally the "incompatible" are not expected to be incorporated into Fe-Ni metal, however, remarkably our own preliminary experimental data indicate that they are enriched in sulfide. At the same time new stable isotope data are also consistent with the incorporation of "incompatible" into sulfide and subsequent migration to the core. That sulfide in the core provides an incompatible element enriched reservoir capable of balancing the composition of the silicate Earth, offers an elegant solution to the non-chondritic Earth. At once reconciling the problem of planetary depletion of the heat-producing elements and providing a heat-source for the geodynamo.The overall aims of this project are (1) to quantify the role of sulfide during Earth's growth and core formation through high-pressure experiments that simulate the conditions of core formation. (2) Assess the influence of sulfide in the core on the composition of Earth's silicate mantle, and (3) the potential influence of continent formation and recycling using neodymium stable isotopes.