New aspects of kimberlite-related metasomatism

与金伯利岩相关的交代作用的新方面

• 批准号: RGPIN-2019-03988
• 负责人: Kopylova, Maya
• 金额: $ 2.19万
• 依托单位: University of British Columbia
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=737324
• 关键词: New; aspects; kimberlite; related; metasomatism

Petrological problems surrounding kimberlites are on the forefront of mantle petrology. We do not yet understand the genesis of kimberlites, as well as their melt compositions in the mantle and in the shallow crust before their emplacement. I will explore the role of metasomatism in 1) pre-conditioning the mantle to the birth of kimberlite melts, and in 2) controlling the mineralogy and textures of kimberlites in the crust. Kimberlite melts are not equilibrated with the ambient mantle, and the enigmatic missing link between kimberlites and the mantle is believed to have formed through mantle metasomatism. We will study megacrysts and fenitized olivinites in contact with carbonatites of alkaline-ultramafic massifs as proxies for the geologic relationships between the metasomatized mantle and kimberlite melts, unavailable for the direct observation at depths >200 km. Independent constraints on metasomatic agents will be obtained from fluids trapped as diamond inclusions in fibrous and octahedrally-grown, gem-quality diamonds and deduced from geochemistry of metasomatic mantle minerals. The second line of research deals with metasomatic reactions between xenoliths of silicic crustal rocks and host kimberlites. Crustal contamination in kimberlites can amount to more than half of the kimberlite volume, significantly impacting the diamond grade and the economics of the mine. Crustal contamination leads to melt hybridization and metasomatic replacement of silicic xenoliths, with mini-skarn reaction zones around the xenoliths. I will investigate the metasomatic transfer of elements in this process and subsequent kimberlite recrystallization and texture development. The proposed research will be based on detailed petrographic, geochemical and mineralogical studies as well as geochemical modelling and petrological experiments. The project is innovative in many ways. It is based on previously uncharacterized occurrences of megacrysts and diamonds, novel trap sites for mantle fluids in diamond fractures, novel massif analogues of kimberlite parent rocks and novel ideas about the genesis of pyroclastic kimberlites. The proposed research will be significant for the fundamental petrology and practical geology. The study of mantle metasomatism will contribute to solving the outstanding problem of the origin of carbonate-rich primary melts in the mantle, their composition, and the composition of their metasomatized mantle source. The practical significance of the proposal relates to the quantification of the diamond ore dilution and recognition of hybrid kimberlite minerals impacting the ore extraction. If we find the causal link between the kimberlite textures, the ore dilution and the country rock architecture, we will be able to predict many major characteristics of diamond deposits simply on the basis of crustal geology.

围绕金伯利岩的岩石学问题是地幔岩石学的前沿。我们还不了解金伯利岩的成因，以及它们在地幔和浅地壳中的熔体成分在他们的侵位之前。我将探讨交代作用在1）预处理地幔金伯利岩熔体的诞生，并在2）控制矿物学和结构的金伯利岩在地壳。金伯利岩熔体与环境地幔不平衡，金伯利岩和地幔之间神秘的缺失环节被认为是通过地幔交代作用形成的。我们将研究与碱性-超镁铁岩的碳酸岩接触的巨晶和细晶化橄榄岩，作为交代地幔和金伯利岩熔体之间地质关系的替代物，无法在深度>200 km处进行直接观察。对交代剂的独立约束将从纤维状和八面体生长的宝石级金刚石中作为金刚石包裹体捕获的流体中获得，并从交代地幔矿物的地球化学中推导出来。第二条研究路线是研究地壳岩石捕虏体与寄主金伯利岩之间的交代反应。金伯利岩中的地壳污染可能占金伯利岩总量的一半以上，严重影响钻石的等级和矿山的经济效益。地壳混染作用导致地幔岩包体的熔融混染和交代交代作用，包体周围形成小型矽卡岩反应带。我将研究在这个过程中的元素的交代转移和随后的金伯利岩重结晶和纹理的发展。 拟议的研究将基于详细的岩石学、地球化学和矿物学研究以及地球化学建模和岩石学实验。该项目在许多方面都具有创新性。它是基于以前未表征的巨晶和金刚石的出现，新的陷阱网站的地幔流体在金刚石断裂，新的金伯利岩母岩的类似物和新的想法的火山碎屑金伯利岩的成因。 该研究对岩石学基础和实际地质都具有重要意义。地幔交代作用的研究将有助于解决地幔中富碳酸盐原生熔体的起源、组成及其交代地幔源区的组成等突出问题。该建议的实际意义涉及到量化的钻石矿石稀释和识别混合金伯利岩矿物影响矿石提取。如果我们找到金伯利岩结构、矿石贫化和围岩结构之间的因果关系，我们将能够简单地根据地壳地质预测金刚石矿床的许多主要特征。