Diamond formation in Earth's mantle

***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，除非在未来几年内发现新的矿藏，否则目前的产量水平将无法持续。为了帮助开发更有效的勘探策略，我们将对远古时期地幔深处促进或阻碍钻石形成的条件进行地球化学指纹分析。*******下面概述的研究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延长的生长历史。我指导了一个多收集器离子微探针设备，这将使我们能够在高空间分辨率下获得钻石生长区域的碳和氮同位素组成和氮含量剖面。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，并揭示它们是含甲烷还是含碳酸盐。通过研究具有已知结晶年龄的钻石，我们将能够跟踪钻石沉淀的首选模式随时间的变化*******2。非常规钻石矿床****太古代克拉通是地壳的大型稳定块，年龄超过25亿年。这些克拉通下方的岩石圈地幔是目前钻石产量的99%以上的来源，而岩石型碳酸盐岩是其关键的钻石基底。然而，地壳的年轻区域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的关键钻石衬底，但我们的初步结果表明，橄榄岩也可能是重要的。我们将研究加拿大地盾下的两个这样的含钻石区域（由Fort <s:1> la Corne的金伯利火山和Victor Mine的金伯利火山取样），这些区域在不到20亿年前受到构造/热事件的强烈影响。通过研究钻石、它们的包裹体和相关的地幔岩石，我们的目标是通过时间来确定这些地区岩石圈地幔中钻石的形成条件*******3。新的加拿大钻石矿床****来自两个新矿床的钻石将用于探测加拿大地盾深层部分的地幔根部：****(1)Chidliak kimberlite油田（巴芬岛）。这个地区被一个小的起源不明的克拉通碎片所覆盖，其钻石源岩尚未被研究。****(2) Gahcho Kue钻石矿。这个矿提供了进入奴隶克拉通南部异常厚的岩石圈地幔的独特途径。*******在所有三个研究主题中获得的知识将对未来加拿大新钻石矿床的勘探至关重要。*******

***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.*******