Mantle Metasomatism and the Origin of Diamonds

地球地幔中的水量可能超过世界上所有海洋、湖泊和河流中的水量。20世纪90年代，在地幔矿物中发现了以羟基（OH）形式存在的水，这一发现意义重大，但这些矿物可能在金伯利岩中从深处上升到地表时发生了变化，金伯利岩也是钻石的宿主。然而，最近在钻石中发现的矿物“环woodite”（Mg2SiO4）中发现了水，这表明水可以长期存在于地幔深处的矿物中。钻石中的矿物包裹体被认为是原始的，因为它们被包裹在数百英里深的地幔中，而地幔正是钻石形成的地方。它们是我们拥有的地球100英里深处部分的唯一样本，也是本提案的主题。特别是地幔中形成钻石的流体，即含水的交代流体，可以揭示钻石及其包裹体形成的条件。拟议研究的主要目标有几个，都与了解交代、热液、碳酸盐岩系统有关，这些系统携带着构成地球内部“隐藏水库”的超临界流体的特征。钻石中的矿物包裹体将从100个不同钻石的捕虏体中选择，该团队此前曾对这些捕虏体进行过研究并发表过文章。具体地说，这项研究将集中于金刚石内含物的化学性质，特别是它们的挥发性含量和同位素组成（例如，硅酸盐中的OH和D/H值；硫化物中的Cl-F-S）。这个更新期将利用该团队有效抛光钻石的能力，同时在一个表面上暴露其众多矿物包裹体。通过对这几种内含物的阴极发光成像，将有可能对它们进行取样，以进一步研究它们的相对年龄，并有可能重现单个钻石生长过程中（可能长达数千万年）不断变化的新陈代谢流体的化学反应。

The amount of water in the mantle of the Earth may exceed that in all the oceans, lakes, and rivers of the world. The finding of water as hydroxyl (OH) in mantle minerals in the 90's was highly significant, but these minerals may have been altered upon ascent from depths to the surface in the kimberlites, also the host for diamonds. However, a recent discovery of water in the mineral 'ringwoodite' (Mg2SiO4) included in a diamond has demonstrated that water can reside within minerals deep in the Earth's mantle for a long time. Mineral inclusions in diamonds are thought to have remained pristine since their encapsulation hundreds of miles deep in the Earth's mantle, where diamonds are formed. They are the only samples we have of the 100 mile-deep portions of the Earth and are the subject of this proposal. In particular, it is the fluids in the mantle that formed the diamonds, the water-bearing metasomatic fluids, which can reveal the conditions responsible for formation of diamonds as well as their inclusions. The main objectives of the proposed research are several, all associated with understanding the metasomatic, hydrothermal, carbonatitic system that carries the signatures of the super-critical fluids that constitute the 'hidden reservoir' of water within the Earth. The mineral inclusions in diamonds will be chosen from the 100 diamondiferous xenoliths, upon which this team has previously studied and published. Specifically, the study will focus on the chemistry of diamond inclusions, particularly their volatile contents and isotope compositions (e.g., OH and D/H values in silicates; Cl-F-S in sulfides). This renewal period will capitalize on this team's ability to effectively polish diamonds, exposing their numerous mineral inclusions simultaneously on one surface. With cathodoluminescence imaging of these several inclusions, it will be possible to sample them for further studies of their relative ages and possibly recreate the chemistry of the changing metasomatic fluids during the individual diamond's lifetime of growth, covering perhaps 10's of millions of years.