Mantle dynamics beneath the North Atlantic region from integrated seismic imaging using new regional seafloor data and global datasets

地幔柱是一种神秘的热上升流，来自地球核心-地幔边界的不稳定。当接近地表时，它们被认为会导致大火成岩省（lip）的就位，这些大火成岩省的灾难性火山活动导致了地球历史上的大规模灭绝。据信，羽流尾部的热物质持续上升，形成了火山热点，持续喷发超过几十英里或更长时间，比如冰岛。地幔柱很难用地震成像，而且LIP岩浆活动在化学上经常变化，并且分散在数千公里之外，这促使人们对LIP和热点火山活动提出了另一种没有地幔柱的解释。地幔柱的特性（从它们的存在开始，根据社区的部分）以及它们是否以及如何导致lip是地球科学中突出的一级问题。冰岛羽流是这种现象的一个典型例子，也是一个长期争论的话题。它被认为是造成冰岛目前火山活动和东北大西洋异常浅（按海底年龄计算）水深的原因。它也可能创造了北大西洋火成岩省（NAIP），其约60万年历史的火山区域从英国分散到格陵兰岛西部。地球物理和岩石学数据表明，冰岛岩石圈下地幔异常热，冰岛和NAIP玄武岩的同位素比值具有深部地幔特征，与羽流起源一致。冰岛羽流是许多地震成像研究的目标，但冰岛周围站点覆盖范围的空白（海底没有站点）导致了地幔数据采样的主要空白。现有的地震模型显示出令人沮丧的低相互一致性。东北大西洋以下的垂直和横向地幔流在很大程度上是未知的。在2018- 2020年，由PI领导的SEA-SEIS项目在东北大西洋的大部分地区运行了海底地震仪（OBS），填补了大部分采样空白。SEA-SEIS自己的重点是爱尔兰近海的结构和地震活动，但该网络也被设计成冰岛羽流的图像。拟议的项目利用了使用独特的新数据的特殊机会（计划在SEA-SEIS端公开发布），而不需要数据收集费用。该项目的目标是突破我们对冰岛羽流的结构和动力学的理解，以及它如何导致NAIP岩浆活动。这将通过将新数据与所有其他可用的相关地震数据相结合，并应用一套互补成像方法来解决羽流结构和羽流引起的流动问题。利用新的和所有已有数据的地震层析成像将产生该地区上下地幔的详细3D图像。我们将把地表和区域S波的波形反演（对上地幔进行采样）与多频远震走时层析成像（也对下地幔进行采样）结合起来。利用接收函数（RF）绘制地幔过渡带（TZ， ~410-660 km深度）的厚度和温度。最近的地图显示了大西洋东北部海底有趣的小规模变化，但在冰岛和英国之间的关键区域却有很大的差距。我们将填补这个空白，并期望了解热羽在哪里以及如何通过TZ上升。波形层析成像和站间表面波测量将约束岩石圈厚度图，并显示薄岩石圈通道是否连接冰岛和东部的NAIP站点。地震各向异性表明岩石在深部流动所形成的结构。它将用互补的剪切波分裂和表面波方法绘制，并显示东北大西洋上地幔对流流动的当前方向。综合的证据将以前所未有的细节阐明冰岛羽流及其产生的对流。它将为全球板内火山作用的机制带来重要的新见解。

Mantle plumes are enigmatic hot upwelling rising from instabilities at Earth's core-mantle boundary. When approaching the surface, they are thought to cause the emplacement of Large Igneous Provinces (LIPs), whose catastrophic volcanism led to mass extinctions through Earth history. Continued ascent of hot material within the plumes' tails is believed to create volcanic hotspots, with continual eruptions over tens of m.y. or more, such as in Iceland. Mantle plumes have been difficult to image seismically, and LIP magmatism is often varied chemically and scattered over thousands of km. This prompted alternative, no-plume explanations for LIP and hotspot volcanism. The properties of mantle plumes (starting with their existence, according to sections of the community) and whether and how they cause LIPs are outstanding, first-order questions of Earth science.The Iceland Plume is a type example of the phenomenon and a subject of long-standing debate. It is thought to cause Iceland's present volcanic activity and the NE Atlantic Ocean's anomalously shallow (per seafloor age) bathymetry. It may also have created the N. Atlantic Igneous Province (NAIP), its ~60 m.y. old volcanic areas dispersed from Britain to western Greenland. Geophysical and petrological data indicate anomalously hot sub-lithospheric mantle below Iceland, and the Iceland and NAIP basalts show isotopic ratios with deep-mantle signatures, consistent with a plume origin.The Iceland Plume was a target of many seismic imaging studies, but the gap in station coverage around Iceland (no stations on the seafloor) translated into major gaps in the data sampling of the mantle. Available seismic models show frustratingly low mutual consistency. The vertical and lateral mantle flow below NE Atlantic is largely unknown. In 2018-20, the project SEA-SEIS, led by the PI, operated Ocean-Bottom Seismometers (OBS) across a large part of NE Atlantic, filling much of the sampling gap. SEA-SEIS' own focus was on structure and seismicity of Ireland's offshore, but the network was designed to also image the Iceland Plume. The proposed project capitalises on the exceptional opportunity of using unique new data (scheduled for public release at SEA-SEIS' end) at no data-collection cost.This project's goal is a breakthrough in our understanding of the structure and dynamics of the Iceland Plume and of how it could cause the NAIP magmatism. This will be achieved by combining the new data with all other relevant seismic data available and applying a suite of complementary imaging methods that will resolve plume structure and plume-induced flow. Seismic tomography with new and all pre-existing data will yield a detailed 3D image of the region's upper and lower mantle. We will combine waveform inversion of surface and regional S waves (sampling the upper mantle) with multi-frequency, teleseismic travel-time tomography (also sampling the lower mantle). The thickness and, by inference, temperature of the mantle transition zone (TZ, ~410-660 km depths) will be mapped using receiver functions (RF). Recent maps show intriguing small-scale variations beneath NE Atlantic but a large gap in the key area between Iceland and Britain. We will fill this gap and expect to learn where and how the hot plume rises through the TZ.Waveform tomography and interstation surface-wave measurements will constrain a lithospheric-thickness map and show whether or not thin-lithosphere channels connect Iceland with NAIP sites to the east.Seismic anisotropy indicates fabric created by flow of the rock at depth. It will be mapped with complementary shear-wave-splitting and surface-wave methods and show current directions of convective flow in the NE Atlantic upper mantle.The combined, integrated evidence will illuminate the Iceland Plume and convective currents it creates in unprecedented detail. It will bring important new insights into the mechanisms of intraplate volcanism globally.