Collaborative Research: Rio Grande Rise: New Questions on Plume Dynamics, Atlantic Tectonic Evolution and an Important Window to the African LLSVP

位于巴西海岸外南大西洋的格兰德河隆起是在中大西洋海脊扩张中心或靠近中大西洋海脊扩张中心形成的火山海洋高原。现在位于非洲以外的沃尔维斯海脊也在同一时间形成于大西洋中部海脊附近。格兰德河隆起的体积大约是沃尔维斯岭的两倍，它们共同记录了约130Myr的板内火山活动，并被假设为代表了深部地幔热柱的产物。尽管它的面积非常大，火山历史也很长，但格兰德河隆起确实是一片隐蔽的土地。根据现有的少数几个岩石样本，格兰德河隆起似乎形成于7000万至9000万年前，与沃尔维斯岭的老部分同时形成。为了了解这些大型火山地貌的历史，该项目将进行一次前往里奥格兰德隆起的海上航行，调查并收集40座海山、裂谷地带山谷和陡峭悬崖的岩石样本。这些新数据将使我们能够彻底调查格兰德河隆起的形成及其与沃尔维斯山脊的关系，那里已经收集了岩石样本。新的数据还将提供一个独特的机会来解决与板块构造有关的一系列问题，包括里奥格兰德隆起与非洲大的低剪切波速度省(LLSVP)的深厚致密地幔带之间的关系，后者被认为是产生地幔热柱的地方。该项目是与巴西科学家和学生合作的。该项目支持美国研究生和本科生的培训。新收集的地质年代学、地球化学和地球物理数据将对以下两个主要科学问题做出重大贡献：(1)里奥格兰德隆起是由烟柱动力学、浅层构造形成的，还是两者兼而有之？对理解热点演化有什么影响？(2)与非洲大型低剪切波速度省(LSVP)深部致密地幔带有关的地幔来源是什么？确定格兰德河隆起和沃尔维斯岭火山活动何时与板内热点火山作用有关是至关重要的，因为这些火山踪迹对于计算1.3亿年前非洲绝对板块运动和全球板块电路模型至关重要。此外，如果里奥格兰德隆起-沃尔维斯山脊系统的大体积及其源区连接回LLSVP的边缘，这将为研究其极端富集组分是否代表下地幔的主要成分提供了独特的可能性。

The Rio Grande Rise in the South Atlantic off of the coast of Brazil is a volcanic oceanic plateau that formed on, or close to the Mid-Atlantic Ridge spreading center. The Walvis Ridge, which is now located off of Africa, also formed near the Mid-Atlantic Ridge close to the same time. The Rio Grande Rise is about twice the volume of Walvis Ridge and together they record ~130 Myr of intra-plate volcanism and are hypothesized to represent the products of a deep mantle plume. Despite its extremely large size and prolonged volcanic history, Rio Grande Rise truly is terra incognita. Based on the few rock samples available, it appears that Rio Grande Rise formed between 70 and 90 million years ago at the same time as the older part of Walvis Ridge. To understand the history of these large volcanic features, this project will carry out a seagoing cruise to the Rio Grande Rise to survey and collect rock samples from 40 seamounts, rift zone valleys and steep escarpments. These new data will allow a thorough investigation of the formation of the Rio Grande Rise and its relationship to the Walvis Ridge where rock samples have already been collected. The new data will also provide a unique opportunity to address a wide range of questions relating to plate tectonics, including how the Rio Grande Rise is related to the deep dense mantle zone of the African large low shear wave velocity province (LLSVP) which is thought to be a place where mantle plumes are generated. This project is in collaboration with Brazilian scientists and students. The project supports the training of U.S. graduate and undergraduate students.The newly collected geochronological, geochemical and geophysical data will contribute significantly to the following two major science questions: (1) Is Rio Grande Rise shaped by plume dynamics, shallow tectonics or both and what are the consequences for understanding hotspot evolution? (2) What are the mantle sources related to the deep dense mantle zone of the African large low shear wave velocity province (LLSVP)? Determining when Rio Grande Rise and Walvis Ridge volcanism became associated with intra-plate hotspot volcanism alone is fundamental as these volcanic traces are essential for calculating African absolute plate motion and global plate circuit models back to 130 million years. Moreover, if the large volume of the Rio Grande Rise-Walvis Ridge system and its source link back to the edge of the LLSVP, this will provide a unique possibility to investigate whether their extreme enriched composition represents a major component in the lower mantle.