Diamond growth and resorption morphologies reveal the record of mantle fluids and melts

钻石的生长和吸收形态揭示了地幔流体和熔体的记录

• 批准号: RGPIN-2020-06718
• 负责人: Fedortchouk, Yana
• 金额: $ 1.82万
• 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: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=750944
• 关键词: Diamond; growth; resorption; morphologies; reveal

Diamonds grow in the Earth's mantle over > 600 km depth range during > 4 Ga (~90% of the Earth's history) and are brought to the surface by kimberlites, the deepest magma that reach the surface of the Earth and host economic diamond deposits. Diamonds are unique witnesses of the conditions and processes in the deep inaccessible parts of the mantle. Some crustal rocks subjected to ultra-high pressure in tectonically active continental areas contain microdiamond inclusions inside other minerals. Volatiles (H2O and CO2) play the major role in diamond nucleation as well as in chemical and geodynamic processes affecting the mantle and super-deep crustal rocks, melt production in the mantle, and the rapid ascent of kimberlites. While the record of volatiles in the composition of rock-forming silicate minerals is ambiguous, an array of dissolution features developed on diamond during interaction with high-temperature fluids and melts in the Earth's interior provide a robust record of these fluids and melts and their conditions (temperature, pressure, oxidation). Crystal shape of microdiamonds from deep crustal rocks depend on the pressure and temperature achieved by these rocks prior to the exhumation. The proposed research uses dissolution features and diamond morphology to study deep fluids in the Earth's crust and mantle, their role in kimberlite magmatism and diamond preservation in kimberlites. The work will combine study of surface features on natural diamonds from different kimberlite types and localities, laboratory experiments that replicate dissolution features and growth morphologies of diamond at controlled conditions, and modeling of atomic scale processes of carbon incorporation and removal on diamond surface to imitate the features and morphologies observed on natural diamonds and establish the reaction-controlling parameters. Collaboration with diamond mining companies and DeBeers provides an exceptional access to diamond samples with geological control from specific depths and units within composite kimberlite pipe. Better understanding sources and composition of fluids in subcontinental mantle and the deep crust is essential for reconstructing the geodynamic processes that shaped the top layers of the Earth and their link to kimberlite magmatism. Magma emplacement mechanisms causing the diversity of kimberlites and affecting diamond distribution and preservation in kimberlites are a subject of controversies. As magma emplacement greatly depends on H2O and CO2 content, the proposed research will use diamond dissolution features as a new method for classifying different kimberlite types and modelling distribution of kimberlite units within composite pipes at early exploration stages to improve geological models and predict diamond preservation. The proposed research will help to unravel deep mantle processes and improve exploration techniques to benefit diamond mining industry in Canada, the third world largest diamond producer.

钻石在 > 4 Ga（约地球历史的 90%）期间在地幔 > 600 公里深度范围内生长，并被金伯利岩带到地表，金伯利岩是到达地球表面并蕴藏经济钻石矿床的最深岩浆。钻石是地幔深处难以到达的部分的条件和过程的独特见证。在构造活跃的大陆地区，一些承受超高压的地壳岩石在其他矿物中含有微金刚石包裹体。挥发物（H2O 和 CO2）在钻石成核以及影响地幔和超深地壳岩石、地幔熔体生产以及金伯利岩快速上升的化学和地球动力学过程中发挥着重要作用。虽然造岩硅酸盐矿物成分中的挥发物记录不明确，但金刚石在与地球内部高温流体和熔体相互作用过程中形成的一系列溶解特征提供了这些流体和熔体及其条件的可靠记录（温度、压力、氧化）。来自深层地壳岩石的微金刚石的晶体形状取决于这些岩石在折返之前所达到的压力和温度。拟议的研究利用溶解特征和钻石形态来研究地壳和地幔中的深层流体及其在金伯利岩岩浆作用和金伯利岩中钻石保存中的作用。这项工作将结合对来自不同金伯利岩类型和产地的天然钻石表面特征的研究、在受控条件下复制钻石溶解特征和生长形态的实验室实验，以及对钻石表面碳吸收和去除的原子尺度过程进行建模，以模拟钻石表面的碳吸收和去除过程。观察天然钻石的特征和形态并建立反应控制参数。与钻石开采公司和戴比尔斯的合作提供了从复合金伯利岩管内的特定深度和单元进行地质控制的钻石样品的特殊获取途径。更好地了解次大陆地幔和地壳深处流体的来源和成分对于重建塑造地球顶层的地球动力学过程及其与金伯利岩岩浆作用的联系至关重要。岩浆侵位机制导致金伯利岩的多样性，影响金伯利岩中钻石的分布和保存，一直是一个有争议的话题。由于岩浆侵位很大程度上取决于 H2O 和 CO2 含量，因此本研究将利用钻石溶解特征作为一种新方法，对不同金伯利岩类型进行分类，并在早期勘探阶段对复合管内金伯利岩单元的分布进行建模，以改进地质模型并预测钻石保存情况。拟议的研究将有助于解开深部地幔过程并改进勘探技术，从而使世界第三大钻石生产国加拿大的钻石采矿业受益。