The influence of lithospheric structure and composition on the distribution of CO2-rich intraplate volcanism and REE mineralisation

岩石圈结构和成分对富CO2板内火山作用和稀土矿化分布的影响

• 批准号: NE/Y000218/1
• 负责人: Sally Gibson
• 金额: $ 106.53万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FY000218%2F1
• 关键词: influence; lithospheric; structure; composition; distribution

Most of the Earth's volcanism occurs at the diverging and converging boundaries of tectonic plates. While igneous activity is less common in intraplate continental settings, these magmas hold essential clues on the evolution of Earth's outer rigid shell (lithosphere) and the generation and distribution of commercially significant natural resources, including rare earth elements (REE) and critical metals (e.g. Nb & Ti), essential for renewable energy and other infrastructure.The type of continental intraplate magmatism is governed by the lithospheric thickness and composition and temperature in the lithosphere and underlying mantle. Intraplate basalts are produced by partial melting in the asthenosphere beneath thin (<60-70 km) lithosphere, whereas carbonatites and associated alkaline igneous rocks, which host most of the world's REE deposits, are emplaced through thicker (~70-120 km) lithosphere. This contrasts with diamondiferous kimberlites and lamproites that occur in Precambrian cratons, with lithosphere over 150 km thick.Carbonatite complexes are found in continental rift zones, Large Igneous Provinces and syn- to post-collisional zones. Previous studies of their origins have largely focused on their relationship with surface geology but here we innovate by examining their distribution with deep lithospheric structure. Our work is timely because:1. It follows the rapid recent growth in the number of seismic stations around the world, which now permits seismic tomography to map lateral variations in lithospheric structure at higher resolution beneath most continental areas than previously possible. High-resolution geophysical models of lithospheric structure together with access to samples collected from global carbonatite complexes of different ages enables novel, unique insights into their distribution in space and time.2. Keeping up with increasing demand to supply REEs, essential for products in emerging clean, green technologies, electronic devices and petroleum-refining catalysts, presents a serious global challenge. Over 95% of the world's usable REEs are produced from the Bayan Obo mine (China), raising concerns over the security of supply for Europe (e.g. EURARE project http://www.eurare.eu/about.html) and highlighting the need to identify sources of potential future deposits. This exploration is essential for long-term planning and growth, but Europe currently has no mines supplying REEs, although there are a number of areas with geology often associated with REE mineralisation, including alkaline igneous rocks found in south-west Greenland, Finland and Scandinavia.The main goal of our research is to quantify the relationship between lithospheric thickness and the global distribution of carbonatite complexes with their associated REE, Ti, Nb and Ta deposits, and assess how this has varied during Earth's evolution. This relates to large-scale, complex interactions within the Earth system. We have conducted pilot studies at global and regional scales, focused on E Africa and western S America, which revealed: (i) a correlation between the distribution of continental magma type and lithospheric thickness; (ii) a strong relationship between carbonatite complexes and the margins of ancient cratons; (iii) Phanerozoic carbonatite magmatism is often located on thinner lithosphere than its Precambrian counterpart. We seek to build on the pilot study by improving the resolution of the geophysical data, expanding the analysis to all the continents, and compiling comprehensive geochemical datasets for carbonatite complexes and associated alkaline igneous rocks of different ages together with their REE deposits. Using in-depth statistical analysis of the geophysical and geochemical data, we will quantify the correlations, establish how they varied over geological time, build a probabilistic predictive model for the location of the rocks and deposits, and advance our knowledge of lithospheric evolution

地球上大多数的火山活动都发生在构造板块的分离和聚合边界上。虽然火成活动在板内大陆环境中不太常见，但这些岩浆对地球外部刚性壳的演化具有重要的线索（岩石圈）和具有商业意义的自然资源，包括稀土元素（REE）和关键金属的生成和分布（例如Nb和Ti），大陆板内岩浆活动的类型取决于岩石圈的厚度和组成，以及岩石圈和下地幔的温度。板内玄武岩是在薄岩石圈（<60-70 km）下的软流圈中部分熔融而产生的，而碳酸岩和伴生的碱性火成岩是通过较厚的岩石圈（~70-120 km）侵位的，它们是世界上大多数稀土矿床的所在地。这与前寒武纪岩石圈厚度超过150 km的含金刚石金伯利岩和钾镁煌斑岩形成鲜明对比。碳酸盐岩杂岩见于大陆裂谷带、大火成岩省和同碰撞至后碰撞带。以前的研究主要集中在它们的起源与地表地质的关系，但在这里，我们通过研究它们的分布与深部岩石圈结构的创新。我们的工作是及时的，因为：1。这是因为最近全世界地震台站的数量迅速增加，使得地震层析成像能够以比以前更高的分辨率绘制大多数大陆地区下面岩石圈结构的横向变化。岩石圈结构的高分辨率地球物理模型以及从不同年龄的全球碳酸盐岩杂岩中收集的样品，使人们能够对它们在空间和时间上的分布有新的、独特的见解。稀土元素是新兴清洁绿色技术、电子设备和石油精炼催化剂产品的必需品，如何满足日益增长的需求是一项严峻的全球挑战。世界上95%以上可用的稀土元素产自（中国）巴彦敖包矿，这引起了人们对欧洲供应安全的担忧（例如EURARE项目http：//www.eurare.eu/about.html），并突出了确定未来潜在矿床来源的必要性。这种勘探对于长期规划和增长至关重要，但欧洲目前没有稀土矿，尽管有一些地区的地质通常与稀土矿化有关，包括格陵兰西南部发现的碱性火成岩，我们研究的主要目标是量化岩石圈厚度与全球碳酸盐岩复合体分布及其相关岩石圈厚度之间的关系。稀土元素，钛，铌和钽矿床，并评估如何在地球的演变过程中发生变化。这涉及到地球系统内大规模、复杂的相互作用。我们在全球和区域范围内进行了试点研究，重点是东非和南美西部，这揭示了：（i）大陆岩浆类型的分布和岩石圈厚度之间的相关性;（ii）碳酸盐岩杂岩和古火山边缘之间的密切关系;（iii）中生代碳酸盐岩岩浆作用往往位于比前寒武纪岩石圈更薄的岩石圈。我们试图通过提高地球物理数据的分辨率，将分析扩展到所有大陆，并为不同年龄的碳酸盐岩复合体和相关碱性火成岩及其稀土矿床编制综合地球化学数据集，以建立在试点研究的基础上。通过对地球物理和地球化学数据的深入统计分析，我们将量化相关性，确定它们如何随地质时间变化，建立岩石和矿床位置的概率预测模型，并提高我们对岩石圈演化的认识