Réunion Island in the western Indian Ocean is well known as one of the most active volcanic hotspots on Earth. Its birth, Ma ago, created the Deccan volcanic traps in India (almost 2 million ), associated with the Cretaceous-Tertiary boundary and with the extinction of about 90% of life on the Earth, including dinosaurs. However, the deep structure of the underlying mantle, the potential presence of a rising plume and its exact geometry in the lower and in the upper mantle are still subjects of debates. The use of seismic data acquired by the French-German RHUM-RUM experiment in the Indian Ocean around the Réunion volcanic hotspot (2012–2013) and the collection of broadband seismic data from temporary experiments and from the FDSN (Federation of Digital Seismograph Networks) data center make it possible to investigate the deep structure of the Réunion mantle plume along its complete track, from its birth to its present stage, with a lateral resolution of km. So far, global seismic tomography models cannot provide such high resolution images of the transition zone or lower mantle in this region. In this study, we used the spectral element method (SEM) to perform waveform forward modeling for several thousand paths beneath the Indian Ocean, and normal mode perturbation theory to compute the gradient and the Hessian for the inverse part of the tomography. Using this hybrid method, we derived a regional tomographic model (including teleseismic and regional events) beneath the Indian Ocean, down to km depth, from simultaneous inversion of fundamental and higher mode three components waveforms down to 40 s period. Our model retrieves a low-velocity channel extending from West to East in the western side of the Central Indian Ridge, in the depth range of 150–250 km. It also reveals a plume conduit with a broad head in the upper mantle and narrow tail anchored in the lower mantle at 1,200 km depth or deeper. The connection between the Réunion hotspot and the South-Africa Large Low-Shear Velocity Province (LLSVP) is also brought to light. Our findings suggest a long-lived Réunion hotspot, since the lower part of the conduit appears to be anchored in the lower mantle, likely fed by the African LLSVP. Our results will guide further geochemical and geodynamic studies on the interaction between the lower transition zone (660–1,000 km) and the deep lower mantle beneath the Réunion hotspot.

中文翻译：

---

留尼汪热点周围印度洋上地幔和中地幔的多模式波形断层扫描

位于印度洋西部的留尼汪岛是众所周知的地球上最活跃的火山热点之一。它的诞生，马前，在印度创造了德干火山圈闭（近 200 万），与白垩纪-第三纪边界以及地球上约 90% 的生命（包括恐龙）的灭绝有关。然而，下地幔的深层结构、上升羽流的潜在存在及其在下地幔和上地幔中的确切几何形状仍然存在争议。使用法国-德国 RHUM-RUM 实验在留尼汪火山热点周围的印度洋（2012-2013 年）获得的地震数据，以及从临时实验和 FDSN（数字地震仪网络联合会）收集的宽带地震数据数据中心使研究留尼汪地幔柱的深层结构成为可能，沿着其完整的轨道，从诞生到现在的阶段，横向分辨率为公里。迄今为止，全球地震层析成像模型无法提供该地区过渡带或下地幔的高分辨率图像。在本研究中，我们使用谱元法 (SEM) 对印度洋下方的数千条路径进行波形正演建模，并使用常模扰动理论计算层析成像反演部分的梯度和 Hessian。使用这种混合方法，我们导出了印度洋下方的区域层析模型（包括远震和区域事件），下至km 深度，从基波和高模三个分量波形的同时反演到 40 s 周期。我们的模型在中印度洋脊的西侧检索了一条从西向东延伸的低速通道，深度范围为 150-250 公里。它还揭示了一个羽状导管，在上地幔中有一个宽阔的头部，在 1,200 公里或更深处锚定在下地幔中的狭窄尾部。留尼汪岛热点与南非大低剪切速度省 (LLSVP) 之间的联系也被曝光。我们的研究结果表明留尼汪岛是一个长期存在的热点，因为管道的下部似乎锚定在下地幔中，可能是由非洲 LLSVP 提供的。我们的结果将指导对下过渡带（660-1，