Rio Grande Rise: A new type of extreme hotspot track, a propagating shear zone, or both?

南大西洋拥有与大陆泛滥玄武岩相连的地幔热柱轨迹的罕见例子之一，它提供了大陆裂谷和新洋盆发展过程中地幔融化的132Myr记录。与该烟柱系统的非洲一侧相比，南美洲一侧的火山岩及其与大陆裂谷和南大西洋开放的关系的现代地质年代学和地球化学数据很少。裂谷作用与丰富的火山作用有关，以巴西边缘的岩脉和向海倾斜的反射体序列为代表，而让·夏科特海山链(JCSC)和里奥格兰德隆起(RGR)在大洋岩石圈上形成了火山结构。这些熔岩中的许多可能与特里斯坦-戈夫岩柱有关，但广泛存在的长期火山作用和地幔断层扫描表明，另一个热点地区产生了另一条火山轨迹，连接了巴西的RGR和侏罗纪溢流玄武岩。我们建议通过使用高精度的地质年代学和地球化学来绘制南美板块火山活动的空间、时间和地球化学演化图，来测试板内岩浆作用和溢流玄武岩起源的相互竞争的模型。我们的目标是首次使用新一代多收集器质谱仪对来自Resende-Ilha Grande脉岩群和巴西边缘、JCSC和RGR的向海倾斜反射层序列的86个样品进行高精度年龄测定。此外，我们还将分析巴西岩脉和向海反射镜玄武岩的主量元素和痕量元素以及锶、钕、氢、铅同位素组成。我们将利用这些新数据来(1)确定RGR是否与巴西东南部侏罗纪洪水玄武岩有关，(2)确定RGR和Walvis海脊的时空发展是否同步或独立，(3)利用这些信息在不同的烟柱和非烟柱模型之间进行检验，特别是我们最近提出的关于南大西洋盆地过去演化的相干地球物理假说。

The South Atlantic Ocean hosts one of the rare examples of a mantle plume track connected to continental flood basalts, which provides a 132 Myr record of mantle melting during continental rifting and development of a new ocean basin. In contrast to the African side of this plume system, very little modern geochronological and geochemical data exist for volcanic rocks on the South American side and its relation with continental rifting and the opening of the South Atlantic. The rifting processes are associated with abundant volcanism represented by dikes and seaward-dipping reflector sequences at the Brazil margin, whereas the Jean Charcot Seamount Chain (JCSC) and of the Rio Grande Rise (RGR) form volcanic structures on the oceanic lithosphere. Many of these lavas may be related to the Tristan-Gough plume, but widespread long-lived volcanism and mantle tomography suggest that another hotspot produced a different volcanic track connecting the RGR to Jurassic flood basalts in Brazil. We propose testing competing models for the origin of intraplate magmatism and flood basalts by using high-precision geochronology and geochemistry to map the spatial, temporal, and geochemical evolution of the volcanism on the South American Plate. We aim to determine for the first time high-precision ages using the next generation of multi-collector mass spectrometer for 86 samples from the Resende-Ilha Grande Dike Swarm and seaward-dipping reflector sequences at the Brazil margin, the JCSC, and the RGR. Additionally, we will analyse the major and trace element and Sr, Nd, Hf, and Pb isotope compositions of the Brazilian dike and seaward-dipping reflector basalts. We will use these new data to (1) establish whether the RGR is connected to Jurassic flood basalts in southeast Brazil, (2) determine if and when the temporal and spatial development of the RGR and Walvis Ridge is synchronous or independent, (3) use this information to test between different plume and non-plume models, in particular our recently proposed coherent geophysical hypothesis about the past evolution of the South Atlantic basin.