Experimental studies of the Earth's mantle

钻石形成于地幔中，深度为bb0 ~130 km，温度为bb1 ~ 900℃。但是关于它们是如何以及为什么形成的，以及它们告诉我们关于它们形成的地幔的什么信息，仍然存在许多问题。我的研究旨在解决这些问题，并更广泛地解决地幔中碳的行为，因为我们需要了解碳稳定为钻石而不是结晶碳酸盐或溶解在流体或熔体中的条件。通过在实验室中再现钻石稳定条件下的地幔压力和温度，我们可以以一种补充其他研究人员对天然钻石及其流体和矿物包裹体的观察的方式来探索这些问题。***我们最近提出了一个钻石形成的模型，其中的关键因素是在钻石稳定的条件下，富含水的流体如何与构成地球上地幔的不同岩石类型相互作用。在某些类型的岩石中，这种流体会引发融化，而钻石必须在这种融化的存在下形成。然而，在与钻石有关的最常见的岩石类型中，不会发生熔化，流体本身可以通过冷却或上升使钻石沉淀。这个模型在思考钻石如何在地幔中形成方面是一个根本性的转变，但我们需要更多地了解钻石在这些流体和熔体中的行为，甚至在这些条件下地幔中可能存在什么样的流体和熔体。这些液体是从哪里来的？一个可能的来源是改变了的海洋地壳和地幔，它们在俯冲带中被再循环到地幔中，并在俯冲到200公里或更深的地方时释放出流体。这些液体会将H2O、CO2、Cl和其他挥发物添加回地幔。前两种已经被广泛研究过，但Cl和其他人还没有。我们想研究当这些流体与地球上地幔的不同岩石类型相互作用时会发生什么。它们什么时候会引发融化？Cl的存在如何改变熔融行为？我们还将研究钻石如何在这些流体与地幔岩石相互作用产生的熔体中溶解，以及这种溶解度如何随压力和温度变化。这将告诉我们这些熔体形成钻石的效率。***最后，一些钻石含有高达5000 ppm的氮。这是否意味着在一些形成钻石的液体或熔体中存在大量或少量的氮？我们将在含氮流体和熔体中培养钻石，以了解氮是如何在这些介质和生长中的钻石之间分配的。***这项研究很重要，不仅从学术角度帮助我们了解钻石是如何形成的，什么样的流体和熔体改变了地球的地幔，而且从更实际的角度来看。钻石是加拿大北部的主要经济驱动力，如果我们能更好地了解钻石是如何形成的，那将为模型提供信息，帮助发现新的矿床。

Diamonds form in the Earth's mantle at depths of > ~130 km and temperatures > ~ 900C. But there remain many questions about how and why they form, and what they tell us about the mantle in which they form. My research aims to address these questions, and addresses the behaviour of carbon in the mantle more broadly, because we need to understand the conditions in which carbon will be stable as diamond rather than as crystalline carbonate or dissolved in a fluid or melt. By reproducing the pressures and temperatures in the Earth's mantle at diamond-stable conditions in the laboratory, we can explore these questions in a way complementary to the observations that other researchers make on natural diamonds and their fluid and mineral inclusions.***We proposed recently a model for diamond formation in which the key element is how a water-rich fluid interacts with the different rock types that make up the Earth's upper mantle at diamond-stable conditions. In some rock types, this fluid would trigger melting, and diamonds would have to form in the presence of that melt. In the most common rock type associated with diamonds, however, melting would not occur, and the fluid itself could precipitate diamond by cooling or ascending. This model is a fundamental shift in thinking about how diamond may form in the mantle, but we need to know more about how diamond behaves in these fluids and melts, and even what kind of fluids and melts could be present in the mantle at these conditions. ***Where do these fluids come from? One likely source is altered oceanic crust and mantle that is recycled into the mantle in subduction zones and gives off fluids as it subducts, down to 200 km depth or more. These fluids would add H2O, CO2, Cl, and other volatiles back into the mantle. The first two have been studied extensively, but not Cl and others. ***We want to study what happens when these fluids interact with the different rock types of the Earth's upper mantle. When will they trigger melting? How does the presence of Cl change the melting behaviour? We will also study how diamond dissolves in melts that are produced by the interaction of these fluids with mantle rocks, and how that solubility changes with pressure and temperature. This will tell us how effective these melts would be in forming diamonds. ***Finally, some diamonds contain up to 5000 ppm nitrogen. Does this mean that there is a lot or only a little nitrogen in some diamond-forming fluids or melts? We will grow diamond in N-bearing fluids and melts to understand how nitrogen partitions between those media and the growing diamond.***This research is important both from an academic perspective helping us to understand how diamond forms and what sort of fluids and melts have modified the Earth's mantle but also from a more practical perspective. Diamonds are a key economic driver in Canada's north, and if we can develop a better understanding of how diamonds form, that will inform models to help find new deposits.