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

了解熔融物如何在地球内部深处（即地幔）聚集，在熔融过程中仍然是地球科学中一个关键和基本的开放问题。这对地球动力学和火山科学等不同主题具有重要意义。虽然熔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，这可能是通过长距离（100公里）横向熔体运输期间宽度为10米至公里的通道网络发生的。然而，通过自然观测来验证这些理论模型并评估不同构造环境中地幔熔体通道化的重要性一直是一个挑战。一个地球动力学环境提供了一个理想的自然实验室来理解熔体的通道化运输，这是地幔柱与附近洋中脊（< 1000 km距离）的相互作用。这是因为来自地幔柱的熔体提供了一个独特的地球化学示踪剂，用于跟踪熔体输送过程。观察到的这类相互作用的关键特征是存在线性火山链（火山线性构造）。一个典型的例子是加拉帕戈斯的沃尔夫-达尔文线性体，这是一个约200公里长的火山特征，从加拉帕戈斯扩张中心以南约250公里处的地幔柱内目前正在发生熔融的区域上方延伸。在我们以前的工作中，我们发现，各种地球物理和地球化学观测的加拉帕戈斯线性自然解释在一个模型中，他们覆盖的网络的挥发性和熔体丰富的渠道连接加拉帕戈斯羽的加拉帕戈斯扩展中心。这样的火山线被发现在其他羽脊相互作用设置在世界各地（如留尼汪，复活节，和发现）。我们建议使用新收集的地球物理数据和新的地球化学观测的加拉帕戈斯线和加拉帕戈斯扩展中心的组合。具体而言，我们建议使用一个阵列的~ 60国家的最先进的宽带海洋仪器，从研究船扔到船外，测量电导率的部分在深度约60至100公里沿着和整个火山线性和羽影响的脊段。合成建模表明，与我们假设的熔体通道相关的电导率信号很可能是可检测的。我们将耦合地球物理调查的结果与地球动力学模型加拉帕戈斯羽流向山脊，以测试我们的研究结果，并区分不同的可能的熔体通道化机制。最后，在地球物理仪器记录数据的同时，我们建议沿北方加拉帕戈斯火山线性构造和线性构造-扩张脊交叉点沿着挖掘火成岩样本。我们将分析它们的地球化学，以限制来自地幔柱的熔体的贡献。这项工作将导致显着的，如果不是变革性的，在我们的理解如何地幔柱附近产生的地球的核幔边界与“浅”的构造特征（洋中脊）相互作用的进步，和地幔熔体的一般运输过程。此外，我们的工作将揭示重要的光在地表系统上的地球深部过程的相互作用。这是因为我们认为代表加拉帕戈斯地幔中熔体输送的表面表现的火山线性构造是东太平洋海洋物种（如鲸鲨）迁移的基础。我们的研究将对这些地形特征如何在洋底形成及其对海洋生态系统的潜在长期影响提供重要的制约因素。

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.