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

地球上的大部分火山活动发生在构造板块的发散和汇聚边界处。虽然火成岩活动在板内大陆环境中不太常见，但这些岩浆对于地球外部刚性壳（岩石圈）的演化以及具有商业意义的自然资源的生成和分布提供了重要线索，包括稀土元素（REE）和关键金属（例如铌和钛），这对可再生能源和其他基础设施至关重要。大陆板内岩浆作用的类型由岩石圈厚度决定 以及岩石圈和底层地幔的成分和温度。板内玄武岩是由薄岩石圈（<60-70 km）下方软流圈的部分熔融产生的，而蕴藏着世界上大部分稀土元素矿床的碳酸岩和相关碱性火成岩则是通过较厚（约70-120 km）岩石圈形成的。这与前寒武纪克拉通中出现的含金刚石金伯利岩和钾长岩形成鲜明对比，岩石圈厚度超过 150 公里。碳酸岩杂岩发现于大陆裂谷带、大型火成岩省和同碰撞到碰撞后区域。以前对它们起源的研究主要集中在它们与地表地质的关系上，但在这里我们通过检查它们在深层岩石圈结构中的分布来进行创新。我们的工作是及时的，因为： 1．最近世界各地地震台数量迅速增长，现在地震层析成像技术能够以比以前更高的分辨率绘制大多数大陆区域下方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代的全球碳酸盐岩复合体中收集的样本，能够对它们在空间和时间上的分布产生新颖、独特的见解。2．稀土元素对于新兴清洁、绿色技术、电子设备和石油精炼催化剂中的产品至关重要，满足日益增长的稀土元素供应需求是一项严峻的全球挑战。全球超过 95% 的可用稀土矿产自白云鄂博矿（中国），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），并强调需要确定未来潜在矿藏的来源。这种勘探对于长期规划和增长至关重要，但欧洲目前没有供应稀土元素的矿山，尽管有许多地区的地质通常与稀土元素矿化有关，包括在格陵兰岛西南部、芬兰和斯堪的纳维亚半岛发现的碱性火成岩。我们研究的主要目标是量化岩石圈厚度与碳酸岩杂岩及其相关稀土元素、钛、铌和钽矿床的全球分布之间的关系，并评估 这在地球的演化过程中是如何变化的。这与地球系统内大规模、复杂的相互作用有关。我们在全球和区域尺度上进行了试点研究，重点关注非洲东部和南美洲西部，结果揭示了：（i）大陆岩浆类型分布与岩石圈厚度之间的相关性； (ii) 碳酸盐岩杂岩与古克拉通边缘之间存在密切关系； (iii) 显生宙碳酸岩岩浆活动通常位于比前寒武纪岩浆更薄的岩石圈上。我们寻求在试点研究的基础上，提高地球物理数据的分辨率，将分析范围扩大到所有大陆，并编制不同年龄的碳酸岩杂岩和相关碱性火成岩及其稀土矿床的综合地球化学数据集。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，确定它们随地质时间的变化，建立岩石和沉积物位置的概率预测模型，并增进我们对岩石圈演化的了解