Deep Mantle Recycling Revealed in Diamonds and their Mineral Inclusions

天然钻石是在地球内部深处的高压和温度下形成的。当钻石形成时，可能来自富含碳酸盐的流体，并在地幔中熔化，它们有时会包裹在地球深处的小块矿物中。这些被称为矿物包裹体。然后，这些钻石在称为金伯利岩的罕见岩浆中从地球深部地幔运往地表。含有这些矿物包裹体的钻石非常罕见，它们提供了一个真正独特的一瞥，让我们得以一窥地球上原本无法到达的部分。一些非常罕见的包裹体提供了地幔过渡带(400-660公里)和下地幔(&gt；660公里)中存在的岩性的直接样本--这些通常被称为超深部钻石。包裹体的化学和矿物相关系提供了有关它们起源的岩性类型的重要信息，并限制了钻石形成的条件和金伯利岩浆形成的深度。因此，超深钻石对于研究地球深处的物质类型、阐明深部地幔过程以及了解碳是如何从地表循环到地幔再回到地表--深层碳循环--非常重要。例如，一些钻石含有与地球表面附近的物质非常相似的物质，如类似洋壳或沉积物的矿物，这些矿物通常具有类似有机碳的碳同位素组成--尽管这是一个有争议的话题。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，这有助于约束地球上地幔对流的质量传递模型。此外，通过测年钻石形成的时间，例如通过包裹体的测年，我们可以有效地对地幔中钻石形成和抬升所涉及的地球动力学过程施加时间限制。适合研究的包裹体钻石非常难得。我们非常幸运地拥有几个大套房(总共有200多颗含钻石)。在巴西著名的Juina地区，金伯利岩管道中的钻石被发现，该地区以超深钻石而闻名。我们之前对Juina地区钻石的研究取得了一些引人入胜的结果，并导致了巴西地下物质回收的模型，我们最近在《自然》杂志上发表了该模型，并在矿物学和岩石学的投稿中发表了该模型。现在，我们希望通过研究Juina的新钻石套件来扩大我们的调查范围，以测试我们目前的模型，并进行高压温度实验，以确定包裹体形成和平衡的深度，并提供必要的信息来限制钻石在固态地幔中的传输速度，可能是在地幔中。在这里，我们提出了一个为期三年的项目，对这些独特的钻石及其矿物包裹体进行全面的矿物学、地球化学、同位素和实验研究。

Natural diamonds are formed at high pressures and temperatures deep within the Earth's interior. When diamonds form, probably from carbonate-rich fluids and melts 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. Some very rare inclusions provide direct samples of lithologies present in the mantle transition zone (400 - 660 km) and the lower mantle (>660 km) - these are often called superdeep diamonds. The chemistry of the inclusions along with mineral phase relations yield important information about the kinds of lithologies they originated in, and constrain the conditions of diamond formation and the depth at which kimberlite magmas form. Thus, superdeep diamonds are very important for studying the types of materials that occur in the deep Earth, for elucidating deep mantle processes, and for understanding how carbon is cycled from the surface to the mantle and back to the surface again - the deep carbon cycle. For example, some diamonds contain materials that are very similar to those occurring near the earth's surface, such as minerals akin to oceanic crust or sediments, and these often have carbon isotopic compositions akin to organic carbon - although this is a controversial subject. 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. Further, by dating when the diamonds formed, for example by dating of inclusions, we can effectively place time constraints in the geodynamic processes involved in diamond formation and uplift in the mantle. Inclusion-bearing diamonds suitable for study are very hard to come by. We are very fortunate to be in possession of several large suites (over 200 inclusion-bearing diamonds in all!) of diamonds from kimberlite pipes in the famous Juina region of Brazil, a region known for its superdeep diamonds. Our previous study on diamonds from the Juina region has yielded some fascinating results, and has led to a model of material recycling beneath Brazil that we have recently published in the journal Nature and in Contributions to Mineralogy and Petrology. We now wish to extend our investigations by studying new suites of diamonds from Juina to test our current model, and to make high-pressure temperature experiments that will allow us to determine at what depths the inclusions formed and equilibrated, and will provide information needed to constrain the rates at which diamonds were transported in the solid-state mantle, possibly in a mantle plume.Here, we propose a three-year project for a comprehensive mineralogical, geochemical, isotopic and experimental investigation of these unique diamonds and their mineral inclusions.