Windows into the Deep: An Investigation of Ultradeep Mineral Inclusions in Natural Diamonds

天然钻石是在地球内部深处的高温高压下形成的。钻石可能是由地幔中富含碳酸盐的流体形成的，它们有时包裹着地球深处的小块矿物。这些被称为矿物包裹体。然后，钻石以一种叫做金伯利岩的罕见岩浆的形式从地幔深处被运送到地表。含有这些矿物包裹体的钻石是非常罕见的，它为我们提供了一个真正独特的机会，让我们得以一窥地球上其他地方无法进入的部分。它们对于研究发生在地球深处的物质类型非常重要。例如，一些钻石含有的物质与地球表面附近的物质非常相似。由此，我们可以得出结论，地表物质可以被输送到很深的地方，这有助于约束地幔对流在地球上的质量传递模型。地球科学中一个长期存在的问题是对流是一个完整的地幔过程还是在地幔中存在离散的对流机制。如果能确定钻石含有形成于地球下地幔的矿物包裹体，这将为全地幔对流模型提供相当大的支持。一些非常罕见的包裹体似乎提供了地幔过渡带（400 / 660公里）和可能的下地幔（>660公里）的岩性的直接样本。包裹体的化学性质以及矿物相关系提供了有关其地幔原岩的重要信息，并限制了钻石形成的条件和金伯利岩岩浆形成的深度。我们很幸运地从巴西的一个金伯利岩管中获得了一套大钻石，其中许多都含有矿物包裹体。我们对这些包裹体的初步研究表明，其中一些包裹体具有独特的化学成分，表明它们的起源非常深——可能在下地幔中。在此，我们提出了一个为期两年的项目，对这些独特的钻石包裹体进行全面的地球化学、同位素和实验研究。通过详细分析它们的化学和同位素组成，我们可以获得关于钻石是如何形成的以及它们内部形成的硅酸盐和氧化物的化学成分的重要信息。此外，通过高压实验了解矿物相关系，我们可以对地幔包裹体的起源深度进行限制。

Natural diamonds are formed at high pressures and temperatures deep within the Earth's interior. When diamonds form, probably from carbonate-rich fluids in the mantle, they sometimes encapsulate small pieces of the minerals that occur at great depth in the Earth. These are called mineral inclusions. The diamonds are then transported from Earth's deep mantle to the surface in uncommon magmas called kimberlites. Diamonds that contain these mineral inclusions are very rare, and offer a truly unique glimpse into what is an otherwise inaccessible portion of the Earth. They are very important for studying the types of materials that occur in the deep Earth. For example, some diamonds contain materials that are very similar to those occuring near the earth's surface. From this, we can conclude that surface materials can be transported to great depth, helping to constrain models of mass transfer in Earth by mantle convection. A longstanding problem in Earth sciences is whether convection is a whole-mantle process or whether there are discrete convecting regimes in the mantle. If diamonds can be identified that have mineral inclusions that formed in Earth's lower mantle, this can give considerable support to a whole-mantle convection model. Some very rare inclusions seem to provide direct samples of lithologies present in the mantle transition zone (400 / 660 km) and possibly the lower mantle (>660 km). The chemistry of the inclusions along with mineral phase relations yield important information about their mantle protoliths, and constrain the conditions of diamond formation and the depth at which kimberlite magmas form. We have been fortunate to obtain a large suite of diamonds from a kimberlite pipe in Brazil, many of which contain mineral inclusions. Our preliminary work on these inclusions has shown that some have unique chemistry indicating a very deep origin - perhaps in the lower mantle. Here, we propose a two-year project for a comprehensive geochemical, isotopic and experimental investigation of these unique diamond inclusions. By analyzing their chemical and isotopic composition in detail we can obtain important information about how the diamonds formed and about the chemistry of the silicate and oxide materials they formed within. Further, by understanding mineral phase relations through high pressure experiments we can place constraints on the depths of origin of the mantle inclusions.