The nature of kimberlitic and mantle fluid and diamond preservation

金伯利岩和地幔流体的性质与钻石保存

• 批准号: 341701-2007
• 负责人: Fedortchouk, Yana
• 金额: $ 1.62万
• 依托单位: Dalhousie University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2008
• 资助国家: 加拿大
• 起止时间: 2008-01-01 至 2009-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=399555
• 关键词: nature; kimberlitic; mantle; fluid; diamond

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.

金伯利岩是形成原生钻石矿床的最深岩浆(&gt；150公里深)。它们填满了只有在各大洲才有的胡萝卜状管道。金伯利岩的起源与深部地幔中的过程有关。金伯利岩将钻石从地幔输送到地表，并在上升过程中部分溶解它们。这种溶解影响了钻石的商业价值和金伯利岩管的钻石等级。金伯利岩富挥发性对金刚石的溶解起着重要作用。目前还不清楚金伯利岩含有多少挥发物以及含有什么类型的挥发物。缺乏这样的知识使我们对金伯利岩起源的理解变得模糊。这项拟议的研究调查了金伯利岩岩浆和地幔流体的挥发分含量和流体系统，并利用这些信息对金伯利岩的来源、原生熔体组成和地幔来源施加新的限制；了解侵位期间的条件和金伯利岩在地表喷发的机制；以及了解是什么导致地幔中的钻石破坏。该计划将使用一种新的方法，基于我最近在研究天然金伯利岩流体系统的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。我的实验结果表明，流体上的H2O/CO2比率决定了钻石上溶解特征的类型。在对新方法进行实验校准后，将使用来自加拿大西北部Lac de Gras金伯利岩的天然钻石块来收集关于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。该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的矿物学、地球化学和岩石学进行研究，以寻找一些地球化学流体指示物，并了解岩浆流体在金伯利岩岩浆结晶和喷发中的作用。所获得的数据将有助于更好地了解金伯利岩的起源、次克拉通地幔中的过程，有助于预测金伯利岩管中钻石的保存和质量。