MANTLE MATERIALS AND CONSTRAINTS ON THE DEEP ANCIENT CARBON CYCLE

地幔物质及其对远古碳循环的制约

• 批准号: RGPIN-2014-04629
• 负责人: Kopylova, Maya
• 金额: $ 3.79万
• 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: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=655888
• 关键词: MANTLE; MATERIALS; CONSTRAINTS; DEEP; ANCIENT

In recent years scientists have focused their efforts on understanding the carbon cycle, from the CO2 degassing of the Earth's interior and the dynamics of atmospheric CO2, to the burial of carbonaceous sediments. Carbonates and other carbon-bearing sediments deposited on the ocean floor are transported into the mantle by subduction. Modern subduction can be monitored by various geophysical, remote sensing and geodynamical methods, but the subduction older than 600 million years and the ancient carbon cycle are very difficult to explore. Below 150 km, carbon from carbonaceous rocks converts to diamond, which can fix and store the carbon for as long as 3.5 billion years. Under rare conditions carbon can escape from the mantle in the form of carbonatitic fluids and join the shallow carbon cycle again. **Despite decades of research these deepest parts of the carbon cycle are the least understood, and the behavior and formation of diamondiferous rocks, diamonds and carbonatitic melts in the mantle are poorly constrained. This impedes our understanding of the carbon fluxes to and from the surface of the Earth, which is required to mitigate global warming. Even more important to us is to know the evolution of carbon fluxes over time. The man-made component of carbon fluxes can be isolated and assessed only if we determine the scale of the natural global change in the cycle. The proposed research provides data on this most ancient and deepest (150-2900 km) part of the carbon cycle. **The research will be based on detailed petrographic, geochemical and mineralogical examination of very rare and scientifically valuable samples. Acquisition of these specimens for research is extremely challenging, as they can only be solicited from diamond exploration companies that spend millions of dollars on drilling and processing. Years of collaborations with industrial partners allowed me to collect many suites of diamonds, mantle xenoliths and kimberlites from various diamond mines globally. I will study diamond collections from recently opened African and Brazilian mines, as well as volcanic rocks that carry diamonds to the surface (kimberlites) and solid fragments of deep-seated diamondiferous rocks entrained in these volcanoes (eclogite xenoliths). The research program will address the following outstanding problems: 1) How eclogites are distributed in the deep interior below ancient continents and what this tells us about the ancient subduction; 2) What type of deep-seated fluids make diamond and provide depositories for carbon below 150 km; 3) Nature's "recipe" for making the most valuable, clear and large gem-quality diamonds; 4) Distinct volcanic processes that prevent an escape of volcanic CO2 from the kimberlite magma into the atmosphere. Overall, the proposed research will constrain the contribution of ancient subduction to the deep carbon cycle in the early Earth, 3 - 0.6 Gy ago, and characterize the processes that lead to carbon storage and/or carbon escape from the mantle.

近年来，科学家们一直致力于了解碳循环，从地球内部的CO2脱气和大气CO2的动力学，到碳质沉积物的埋藏。沉积在洋底的碳酸盐和其他含碳沉积物通过俯冲作用进入地幔。现代俯冲作用可以通过各种地球物理、遥感和地球动力学方法进行监测，但6亿年以上的俯冲作用和古代碳循环是很难探索的。在150公里以下，碳质岩石中的碳转化为金刚石，金刚石可以固定和储存碳长达35亿年。在罕见的情况下，碳可以以碳酸岩流体的形式从地幔中逸出，并再次加入浅层碳循环。** 尽管经过数十年的研究，碳循环的这些最深处仍是人们了解最少的，地幔中含金刚石岩石、金刚石和碳酸岩熔体的行为和形成也受到很大的限制。这阻碍了我们对地球表面碳通量的理解，而这是减缓全球变暖所必需的。对我们来说，更重要的是了解碳通量随时间的演变。只有确定了循环中全球自然变化的规模，才能分离和评估碳通量的人为成分。拟议的研究提供了碳循环中最古老和最深（150-2900公里）部分的数据。** 研究将基于对非常稀有和具有科学价值的样品进行详细的岩相学、地球化学和矿物学检查。获取这些标本用于研究极具挑战性，因为它们只能从钻石勘探公司那里获得，这些公司花费数百万美元进行钻探和加工。多年来与工业合作伙伴的合作使我能够从全球各地的钻石矿中收集许多钻石，地幔捕虏体和金伯利岩。我将研究最近开放的非洲和巴西矿山的钻石收藏品，以及将钻石带到地表的火山岩（金伯利岩）和这些火山中夹带的深层含金刚石岩石的固体碎片（榴辉岩捕虏体）。该研究计划将解决以下悬而未决的问题：1）榴辉岩如何分布在古代大陆下方的深部内部，以及这告诉我们关于古代俯冲的信息; 2）什么类型的深部流体制造金刚石并为150公里以下的碳提供矿床; 3）大自然制造最有价值的、透明的和大宝石级金刚石的“配方”; 4）独特的火山作用，阻止火山二氧化碳从金伯利岩岩浆逃逸到大气中。总的来说，拟议的研究将限制古代俯冲作用对地球早期（3 - 0.6戈伊前）深部碳循环的贡献，并描述导致碳储存和/或碳从地幔逃逸的过程。