Mantle metasomatism and kimberlite emplacement recorded in the dissolution and reaction products on diamond and other mantle minerals

金刚石和其他地幔矿物的溶解和反应产物记录的地幔交代作用和金伯利岩侵位

• 批准号: RGPIN-2015-04650
• 负责人: Fedortchouk, Yana
• 金额: $ 1.6万
• 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: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=613087
• 关键词: Mantle; metasomatism; kimberlite; emplacement; recorded

Diamond forms deep in the mantle and is carried upwards to the Earth’s surface by the deepest known magma, kimberlites. Our modern knowledge of diamond internal structure and inclusions implies a complex history of interaction with melts and fluids, which percolate through the mantle beneath the continents modifying its composition. The complexity of the diamond carrier, kimberlite magma, precludes the usage of conventional methods to study kimberlites leaving their origin ambiguous. The proposed research offers a novel approach for investigating deep magmas and fluids by uncovering the record, which they leave on the surface of diamond and other mantle minerals during interaction. Experiments carried out at the conditions simulating the natural environments will explore development of surface features on diamond during dissolution. Comparing these features to those on natural diamonds will test the exiting hypotheses of the complex chemical processes in the different domains of subcontinental mantle and the hypotheses of the composition of kimberlite melt, the behavior of volatiles, and their effect on kimberlite emplacement. The proposed study will use diamonds obtained from different sections of composite kimberlite pipes. This unique opportunity to study diamond parcels with geological control is possible due to the support of my research by diamond industry. In order to derive a predictive model applicable to natural kimberlites, I am developing a quantitative method to study diamond morphology using atomic force microscopy. This approach provides three-dimensional dataset of mineral surface and allows to quantify the H2O:CO2 ratio and temperature of diamond-destructive fluids. The results of this work will complement the studies of diamond mineral inclusions and isotope systematic to resolve fundamental questions related to the origin of kimberlite magmatism, processes triggering diamond growth, and complex chemical processes modifying the subcontinental mantle. The anticipated results will establish the mechanism of diamond interaction with fluids and explain the variety of surface features observed on natural diamonds, which origin is not yet understood. The project will advance modeling of the oxidation state of the Earth’s mantle, provide new robust constraints on the nature of fluids in different mantle environments, and compare the evolution of the deep continental roots beneath North America and Africa. The study will address important exploration problem of diamond preservation. Diamond dissolution may result in significant diamond loss and decrease in diamond grade. If substantial dissolution occurs in the kimberlite magma the decrease in diamond grade may not be apparent from the existing methods for diamond potential assessment. The proposed research will provide new tools for improving exploration techniques and assessment of kimberlite bodies.

钻石形成于地幔深处，并被已知最深的岩浆——金伯利岩——带到地球表面。我们对钻石内部结构和包裹体的现代知识表明，它与熔体和流体相互作用的复杂历史，这些熔体和流体通过大陆下面的地幔渗透，改变了它的组成。钻石载体金伯利岩岩浆的复杂性，使传统方法无法研究金伯利岩，使其起源模糊不清。这项研究为研究深部岩浆和流体提供了一种新的方法，通过揭示它们在相互作用过程中留在钻石和其他地幔矿物表面的记录。在模拟自然环境的条件下进行的实验将探索金刚石在溶解过程中表面特征的发展。将这些特征与天然钻石的特征进行比较，将检验现有的关于次大陆地幔不同区域复杂化学过程的假设，以及关于金伯利岩熔体成分、挥发物行为及其对金伯利岩侵位的影响的假设。拟议的研究将使用从复合金伯利岩管道的不同部分获得的钻石。由于我的研究得到了钻石行业的支持，这个独特的机会可以研究具有地质控制的钻石包裹。为了推导出一种适用于天然金伯利岩的预测模型，我正在开发一种定量方法，利用原子力显微镜研究钻石的形态。该方法提供了矿物表面的三维数据集，并允许量化H2O:CO2比和钻石破坏流体的温度。这项工作的结果将补充钻石矿物包裹体和同位素系统的研究，以解决与金伯利岩岩浆作用的起源、触发钻石生长的过程以及改变次大陆地幔的复杂化学过程有关的基本问题。预期的结果将建立钻石与流体相互作用的机制，并解释在天然钻石上观察到的各种表面特征，这些特征的起源尚不清楚。该项目将推进地球地幔氧化态的建模，为不同地幔环境下的流体性质提供新的强有力的约束，并比较北美和非洲地下深层大陆根的演化。该研究将解决重要的钻石保存勘探问题。钻石溶解会导致钻石的严重损失和钻石品位的降低。如果在金伯利岩岩浆中发生了大量的溶解，那么从现有的钻石潜力评价方法来看，钻石品位的下降可能并不明显。提出的研究将为改进金伯利岩体的勘探技术和评价提供新的工具。