The nature of kimberlitic and mantle fluid and diamond preservation

金伯利岩是最深处的岩浆（约150公里深），形成钻石的原始矿床。它们填满胡萝卜状的管子，这种管子只有在大陆上才有。金伯利岩的起源与深部地幔的作用有关。金伯利岩将钻石从地幔运送到地表，并在上升过程中部分溶解钻石。溶蚀影响金伯利岩管的钻石商业价值和钻石品位。金伯利岩的富挥发物性质在金刚石溶解过程中起着重要作用。目前尚不清楚金伯利岩中含有多少挥发物和哪种挥发物。缺乏这方面的知识使我们对金伯利岩起源的认识模糊不清。本文研究了金伯利岩岩浆和地幔流体的挥发性成分和流体体系，并利用这些信息对金伯利岩的成因、初级熔体成分和地幔来源提出了新的限制；了解就位时的条件和地表金伯利岩喷发机制；并了解是什么导致了地幔中钻石的破坏。本项目将根据本人近期实验研究中发现的金伯利岩岩浆流体相与钻石表面特征之间的关系，采用一种新的方法研究天然金伯利岩流体系统。我的实验结果表明，液体的H2O/CO2比决定了钻石的溶解特征类型。在对新方法进行实验校准后，将利用来自Lac de Gras金伯利岩（n.w.t., Canada）的天然钻石包裹来收集钻石表面特征的详细数据，以确定这些金伯利岩中岩浆流体的组成和演化。本研究还将利用传统的分析技术，对Lac de Gras金伯利岩和金伯利岩指示矿物进行矿物学、地球化学和岩石学研究，以寻找一些地球化学流体指示物，了解岩浆流体在金伯利岩岩浆结晶和喷发中的作用。获得的数据将有助于更好地了解金伯利岩的起源、次克拉通地幔的过程，并有助于预测金伯利岩管中钻石的保存和质量。

Kimberlites are the most deep-seated magmas (>150 km depth) that form primary deposits of diamonds. They fill carrot-shape pipes found only within continents. The origin of kimberlites is linked to processes in the deep mantle. Kimberlites transport diamonds from the Earth's mantle to the surface and partially dissolve them during the ascent. The dissolution impacts the commercial value of diamonds and the diamond grade of a kimberlite pipe. Volatile-rich nature of kimberlites plays an important role in diamond dissolution. It is not well known how much and what kind of volatiles kimberlites contain. Lack of such knowledge obscures our understanding of the origin of kimberlites. The proposed research investigates volatile content and fluid system of kimberlite magmas and the mantle fluid, and uses this information to put new constraints on the origin, primary melt composition and mantle source of kimberlites; to learn about conditions during emplacement and the mechanism of kimberlite eruption at the surface; and to understand what causes diamond destruction in the mantle. The program will use a new method based on the relationship between the fluid phase of kimberlite magma and the surface features on diamonds discovered in my recent experimental study to investigate fluid system of natural kimberlites. The results of my experiments show that the H2O/CO2 ratio on the fluid determines the type of dissolution features on diamonds. After experimental calibration of the new method, natural diamond parcels from Lac de Gras kimberlites (N.W.T., Canada) will be used to collect detailed data on the diamond surface features in order to determine composition and evolution of magmatic fluid in these kimberlites. The research will also use traditional analytical techniques to study mineralogy, geochemistry and petrography of the Lac de Gras kimberlites and kimberlite indicator minerals in order to find some geochemical fluid indicators and to understand the role of magmatic fluid in the crystallization and eruption of kimberlite magmas. The obtained data will provide better understanding of the origin of kimberlites, processes in subcratonic mantle, will help to predict preservation and quality of diamonds in a kimberlite pipe.