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: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=611151
• 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，科学家将精力集中在理解碳循环上，从地球内部的二氧化碳脱水和大气二氧化碳的动态到埋葬碳质沉积物的埋葬。沉积在海底上的碳酸盐和其他含碳沉积物通过俯冲将其运输到地幔中。现代俯冲可以通过各种地球物理，遥感和地球动力学方法来监测，但是俯冲年龄超过6亿年，古老的碳循环很难探索。低于150公里的碳岩碳将碳转换为钻石，可以将碳固定和存储长达35亿年。在极少数情况下，碳可以以碳含水的形式从地幔中逸出，并再次连接浅碳循环。 尽管研究了数十年的研究，但碳循环中最深的部分的理解最低，地幔中钻石岩石，钻石和碳质融化的行为和形成受到限制。这阻碍了我们对地球表面和从地面的碳通量的理解，这是减轻全球变暖所必需的。对我们来说，更重要的是要知道随着时间的流逝，碳通量的演变。只有当我们确定周期中自然全局变化的规模时，才能分离并评估碳通量的人为成分。拟议的研究提供了有关碳循环中最古老，最深（150-2900公里）部分的数据。 这项研究将基于对非常稀有和科学有价值的样本的详细岩石学，地球化学和矿物学检查。这些物种进行研究是极为挑战的，因为它们只能从花费数百万美元进行钻探和加工的钻石勘探公司中巩固。多年与工业合作伙伴的合作使我能够从全球各种钻石矿山收集许多钻石，披风异性石和金伯利岩的套房。我将从最近开放的非洲和巴西矿山中研究钻石收集，以及将钻石带到地表（金伯利岩）的火山岩和深层钻石岩石的固体碎片，这些岩石岩石中充满了这些火山（Eplogite oglogite xenoliths）。该研究计划将解决以下杰出问题：1）如何在古代大陆以下的深层内部分布叶绿树，以及有关古代俯冲的信息； 2）哪种类型的深座液会制造钻石，并为150公里以下的碳提供沉积； 3）大自然的“食谱”是制造最有价值，最清晰，最大的宝石品质钻石； 4）不同的火山过程，以防止火山二氧化碳从金伯利岩岩浆逃脱到大气中。总体而言，拟议的研究将限制古代俯冲对地球早期深碳循环的贡献，3-0.6 Gy以前，并表征导致碳储存和/或碳从地幔中逸出的过程。