Diamond formation in Earth's mantle

地幔中的钻石形成

• 批准号: RGPIN-2017-06041
• 负责人: Stachel, Thomas
• 金额: $ 3.42万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=689459
• 关键词: Diamond; formation; Earth; mantle

***Diamond exploration and mining is the principal economic driving force in Canada's remote North. However, current levels of production will be unsustainable unless new deposits are discovered within the next few years. To help develop more efficient exploration strategies, we will geochemically fingerprint the conditions deep in the Earth's mantle that enhanced or prevented diamond formation in the distant past.*******The investigations outlined below are expected to produce not only ground-breaking basic research but also new and better methods for diamond exploration.*******1. Processes of diamond formation****The layered internal structure of diamond can be compared to tree rings in that both can reveal complex and extended growth histories. I direct a multi-collector ion microprobe facility, which will enable us to obtain profiles of carbon and nitrogen isotopic compositions and nitrogen contents at high spatial resolution across diamond growth zones. These profiles allow us to deduce the chemical character of the original diamond-forming fluids or melts and reveal if they were methane- or carbonate-bearing. By studying diamonds with known ages of crystallization, we will be able to follow variations in the preferred modes of diamond precipitation through time.*******2. Unconventional diamond deposits****Archean cratons are large, stable blocks of the Earth's crust that are older than 2.5 billion years. The lithospheric mantle beneath such cratons is the source of >99% of current diamond production, and the rock type harzburgite is its key diamond substrate. However, younger areas of the crust can also host world-class diamond deposits. The rock type eclogite is a key diamond substrate in such unconventional deposits, but our preliminary results suggest that lherzolite may also be important. We will investigate two such diamond-bearing areas beneath the Canadian Shield (sampled by kimberlite volcanoes at Fort à la Corne and the Victor Mine) that were strongly affected by tectonic/thermal events less than two billion years ago. By studying the diamonds, their inclusions, and the associated mantle rocks, we aim to determine the diamond-forming conditions in the lithospheric mantles of these areas through time.*******3. New Canadian diamond deposits****Diamonds from two new deposits will be used to probe the mantle roots of little-studied deep sections of the Canadian Shield:****(1) The Chidliak kimberlite field (Baffin Island). This area is underlain by a small cratonic fragment of unclear origin, and its diamond source rocks have not yet been investigated.****(2) The Gahcho Kue diamond mine. This mine provides unique access to an exceptionally thick section of lithospheric mantle in the southern Slave Craton.*******The knowledge gained in all three study themes will be crucial to future exploration for new diamond deposits in Canada.*******

* 钻石勘探和开采是加拿大偏远北部地区的主要经济驱动力。然而，除非在今后几年内发现新的矿藏，否则目前的生产水平将无法持续。为了帮助制定更有效的勘探策略，我们将对遥远过去促进或阻止钻石形成的地球地幔深处的条件进行地球化学指纹分析。**下面概述的调查预计不仅会产生突破性的基础研究，而且会产生新的和更好的钻石勘探方法。1.金刚石的形成过程 **** 金刚石的层状内部结构可以与树木的年轮相比较，因为两者都可以揭示复杂和扩展的生长历史。我直接多收集器离子微探针设施，这将使我们能够获得高空间分辨率的碳和氮同位素组成和氮含量在整个金刚石生长区的配置文件。这些剖面使我们能够推断出原始钻石形成流体或熔体的化学特征，并揭示它们是否含有甲烷或碳酸盐。通过研究已知结晶年龄的金刚石，我们将能够跟踪金刚石沉淀的优选模式随时间的变化。2.非常规钻石矿床 * 太古代钻石是地壳中巨大而稳定的块体，年龄超过25亿年。在这些岩石圈地幔之下的岩石圈地幔是超过99%的当前金刚石产量的来源，而岩石类型的哈兹伯拉是其关键的金刚石基底。然而，地壳较年轻的地区也可能拥有世界级的钻石矿床。 岩石型榴辉岩是这类非常规矿床中的关键金刚石基质，但我们的初步研究结果表明，二辉橄榄岩也可能很重要。我们将调查加拿大地盾下的两个这样的钻石产区（以科尔内堡和维克托矿的金伯利岩火山为样本），这些地区受到不到20亿年前的构造/热事件的强烈影响。通过研究金刚石、它们的包裹体和相关的地幔岩石，我们的目标是确定这些地区岩石圈地幔中金刚石随时间的形成条件。3.加拿大新的钻石矿床 * 来自两个新矿床的钻石将用于探测加拿大地盾很少研究的深部地幔根：*（1）奇德利亚克金伯利岩区（巴芬岛）。该地区下面是一个起源不明的小碎屑岩，其金刚石源岩尚未调查。(2)Gahcho Kue钻石矿。这个矿提供了一个独特的进入一个异常厚的岩石圈地幔部分在南部的奴隶。在所有三个研究主题中获得的知识将对加拿大未来勘探新的钻石矿床至关重要。