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: 2012
• 资助国家: 加拿大
• 起止时间: 2012-01-01 至 2013-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=496904
• 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.

金伯利岩是形成金刚石原生矿床的最深层岩浆（深度>150公里）。它们填充着只有在大陆上才能找到的胡萝卜形状的管道。金伯利岩的起源与地幔深处的过程有关。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它们。溶解影响钻石的商业价值和金伯利岩管的钻石等级。金伯利岩富含挥发分的性质在金刚石溶解过程中起着重要作用。金伯利岩中含有多少挥发性物质以及何种挥发性物质尚不清楚。缺乏这种知识模糊了我们对金伯利岩起源的理解。拟议的研究调查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起源，原始熔体成分和地幔来源提出新的限制;了解金伯利岩侵位期间的条件和表面喷发的机制;并了解是什么原因导致地幔中的金刚石破坏。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金刚石表面特征之间的关系，采用一种新的方法来研究天然金伯利岩的流体体系。实验结果表明，流体中的H_2O/CO_2比值决定了金刚石的溶解特征类型。在新方法的实验校准之后，来自Lac de Gras金伯利岩（N.W.T.，加拿大）将用于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。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进行矿物学、地球化学和岩相学研究，以寻找一些地球化学流体指标，了解岩浆流体在金伯利岩岩浆结晶和喷发中的作用。所获得的数据将提供更好地了解金伯利岩的起源，在亚地幔的过程，将有助于预测保存和质量的钻石在金伯利岩管。