NSFGEO-NERC: Magnetotelluric imaging and geodynamical/geochemical investigations of plume-ridge interaction in the Galapagos

NSFGEO-NERC：加拉帕戈斯群岛羽流-山脊相互作用的大地电磁成像和地球动力学/地球化学研究

• 批准号: NE/Z000254/1
• 负责人: Sally Gibson
• 金额: $ 31.7万
• 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: 2025
• 资助国家: 英国
• 起止时间: 2025 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FZ000254%2F1
• 关键词: NSFGEO; NERC; Magnetotelluric; imaging; geodynamical

Understanding how melt aggregates in our planet's deep interior, i.e. its mantle, during melting remains a critical and fundamental open question in the Earth Sciences. This has important impliactions for topics as diverse as geodynamics and volcano science. Although the transport of melt in the mantle has been typically modelled as being a diffuse process, a variety of geological, geochemical, experimental and theoretical results suggest that this might occur via a network of channels that are 10s of m to km in width during long-distance (100s of km) lateral melt transport. However, it has been challenging to validate these theoretical models via natural observations and assess the importance of melt channelisation in the mantle across different tectonic settings.One geodynamic setting that provides an ideal natural laboratory to understand this channelised transport of melt is the interaction of mantle plumes with nearby mid-ocean ridges (< 1000 km distance). This is because melts derived from a mantle plume provide a distinct geochemical tracer for tracking melt transport processes. The key observed characteristic of this type of interaction is the presence of linear chains of volcanoes (volcanic lineaments). A classic example is the Wolf-Darwin Lineament in Galápagos, a ~ 200 km long volcanic feature extending from above a region where there is currently melting taking place within a mantle plume located ~ 250 km south of the Galápagos Spreading Centre. In our previous work we find that a variety of geophysical and geochemical observations for the Galápagos lineaments are naturally explained in a model where they overlie a network of volatile- and melt-rich channels connecting the Galápagos plume to the Galápagos Spreading Centre. Such volcanic lineaments are found in other plume-ridge interaction settings worldwide (e.g. Reunion, Easter, and Discovery).We propose to use a combination of newly collected geophysical data and novel geochemical observations of the Galápagos lineaments and the Galápagos Spreading Centre. Specifically, we propose to use an array of ~ 60 state-of-the-art broadband marine instruments, dropped overboard from the research ship, to measure electrical conductivity in sections at depths of ~60 to 100 km along and across the volcanic lineaments and the plume-affected ridge segments. Synthetic modelling demonstrates that the conductivity signals associated with the melt channels that we hypothesize are very likely to be detectable. We will couple the results from the geophysical survey with geodynamical models for Galápagos plume flow towards the ridge in order to test our findings and discern among the different possible melt channelisation mechanisms. Finally, while the geophysical instruments are recording data, we propose to dredge samples of igneous rocks along both the northern Galápagos volcanic lineaments and the lineament-spreading ridge intersections. We will analyse these for their geochemistry in order to constrain the contribution of melts from the mantle plume. This work will lead to significant, if not transformative, advances in our understanding of how mantle plumes generated near Earth's core-mantle boundary interact with 'shallow' tectonic features (mid-ocean ridges), and mantle melt transport processes in general.Furthermore, our work will shed important light on the interaction of deep Earth processes on surface systems. This is because the volcanic lineaments that we believe represent the surface expressions of melt transport in the mantle in the Galapagos are fundamental to the migration of marine species in the eastern Pacific (e.g. whale sharks). Our study will provide important constraints on how these topographic features form on the ocean floor and also their potential long-term influence on marine ecosystems.

了解融水如何在地球的深层内部，即地幔中聚集，在融化过程中，仍然是地球科学中一个关键和基本的开放性问题。这对地球动力学和火山科学等各种主题具有重要意义。虽然熔融体在地幔中的运输通常被模拟为一个扩散过程，但各种地质、地球化学、实验和理论结果表明，在长距离（100公里）的横向熔融体运输过程中，这可能通过一个宽度为10米至10公里的通道网络发生。然而，通过自然观测来验证这些理论模型并评估不同构造背景下地幔中熔融通道化的重要性一直具有挑战性。地幔柱与附近洋中脊（距离小于1000公里）的相互作用是一个地球动力学背景，它为理解这种通道化的熔融输送提供了一个理想的自然实验室。这是因为源自地幔柱的熔体为追踪熔体运输过程提供了一种独特的地球化学示踪剂。观测到的这种相互作用的关键特征是火山线状链（火山线状）的存在。一个典型的例子是Galápagos的沃尔夫-达尔文线条，这是一个长约200公里的火山特征，从位于Galápagos扩张中心以南约250公里处的地幔柱中正在融化的区域上方延伸出来。在我们之前的工作中，我们发现Galápagos的各种地球物理和地球化学观测结果都可以在一个模型中自然地解释，在这个模型中，它们覆盖在连接Galápagos羽流和Galápagos扩散中心的富含挥发物和熔体的通道网络上。在世界范围内其他羽状脊相互作用环境（如留尼旺、复活节和发现）中也发现了这种火山特征。我们建议结合新收集的地球物理数据和新的地球化学观测，对Galápagos和Galápagos扩张中心进行研究。具体来说，我们建议使用一组约60台最先进的宽带海洋仪器，从科考船上扔下来，沿着火山轮廓和受羽流影响的脊段测量60至100公里深度部分的电导率。合成模型表明，我们假设的与熔体通道相关的电导率信号很可能被检测到。我们将把地球物理调查的结果与Galápagos羽流向山脊的地球动力学模型结合起来，以检验我们的发现并辨别不同可能的融化通道化机制。最后，在地球物理仪器记录数据的同时，我们建议沿Galápagos北部火山线和线展脊交叉点进行火成岩取样。我们将对它们进行地球化学分析，以限制地幔柱熔体的贡献。这项工作将导致我们对地幔柱如何在地球核-地幔边界附近产生与“浅层”构造特征（洋中脊）相互作用以及地幔熔体运输过程的理解取得重大进展。此外，我们的工作将对地表系统的深层地球过程的相互作用提供重要的启示。这是因为我们认为，火山地貌代表了加拉帕戈斯群岛地幔中熔体运输的表面表现，是东太平洋海洋物种（如鲸鲨）迁徙的基础。我们的研究将为这些地形特征如何在海底形成以及它们对海洋生态系统的潜在长期影响提供重要的限制。