Collaborative Research: Evolution of the Tristan-Gough-Walvis Ridge Hotspot System: Age and Composition of Expedition 391/397T Volcanic Basement

热点是起源于地核-地幔边界附近的地幔中异常温暖的区域。它们在板块构造中发挥着重要作用，是大陆分裂和随后形成新海洋的主要驱动力之一。随着大陆碎片的漂移和新的海洋在陆块之间形成，有影响力的热点仍然存在。然后，这个热点在新的海底产生了一系列较小的火山爆发。这些喷发对深部热点进行取样，在某些情况下，对浅地幔进行取样。然而，浅地幔的成分并不均匀。相反，它随着大陆漂移和新的海底形成而演变。为了更好地了解热点在形成新海底中的作用以及随着海洋盆地的成熟，浅地幔如何变化，国际海洋发现计划（IODP）第391和397 T号考察队沿着南大西洋的沃尔维斯海岭沿着钻探了六座不同的水下火山。沃尔维斯海岭由一系列水下火山组成，这些火山是在非洲从南美洲分离和南大西洋形成期间由热点形成的。该项目将利用在六个地点获得的岩心样本调查三个主要问题。首先，上地幔对沃尔维斯海岭火山活动的贡献有多大？是什么决定了上地幔与热点对沃尔维斯海岭火山作用的贡献的比例？最后，随着大陆漂移和南大西洋扩张，上地幔是如何变化的。该项目支持美国和国际科学家之间的合作。它还将资助传统上在地球科学中代表性不足的学生（美洲原住民，黑人，LGBTQ等）的本科生和研究生研究。该项目的总体目标是更好地了解与南大西洋大陆裂谷和洋盆形成有关的岩浆过程，从白垩纪早期开始，一直持续到今天。为此，IODP Expeditions 391和397 T沿着沿着Tristan-Gough-Walvis Ridge（TGW）热点轨道钻探了6个地点，跨度为1200公里，玄武岩基底约620米。钻探地点沿着TGW取样的空间和时间范围很大：一个地点在Frio Rise（邻近非洲大陆），两个地点在Valdivia Bank（与格兰德河Rise同源，形成于早期大西洋中脊附近），三个位于“三叉戟”上的盖奥特，通往Tristan da库尼亚和Gough火山岛。该项目将与科学小组的其他成员合作，对回收的玄武岩核心进行全面的地球化学和地质年代学研究，以记录随着裂谷和海底扩张的进展，热点与上覆岩石圈之间不断变化的地球动力学相互作用。该小组将收集大量数据，包括地质年代学（邓肯希顿，俄勒冈州立大学），全岩地球化学（纳尔逊，TU; Potter Shervais，USU），矿物和相关熔体包裹体化学（Potter Shervais，USU），惰性气体丰度和同位素特征（Dygert Scholpp，UTK），熔岩的氧逸度表征（Dygert Scholpp，UTK）和全岩Re-Os同位素组成（纳尔逊，TU）。该小组将利用这些数据检验基于初步工作的三个假设：（1）熔岩化学将从东北部的Etendeka大火成岩省向西南部的Gough和Tristan de库尼亚的板内洋岛演化，这与岩浆流量随时间减少和熔体来源变化相一致;（2）岩浆流量随时间变化，并与其他地质特征（如扩张脊、非洲大陆等）的接近程度有关;（3）靠近扩张脊的熔岩中，类MORB岩浆（DMM源）的比例高于热点源。在小范围内，在各个钻探地点获得的高质量岩心提供了一个独特的窗口，可以了解单个海山形成时的时间和地球化学变化，以及这种变化如何随着靠近扩张脊而变化。在更大的范围内，这项工作将提供一个无与伦比的看看如何羽脊相互作用随着时间的推移而变化。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

Hotspots are anomalously warm regions in the Earth’s mantle originating near the core-mantle boundary. They play an important role in plate tectonics as one of the primary drivers of continental break up and the subsequent formation of new oceans. As continental fragments drift apart and new oceans form between the land masses, the influential hotspot persists. This hotspot then creates a series of smaller volcanic eruptions on the new seafloor. These eruptions sample the deep hotspot and, in some cases, the shallow mantle. However, the shallow mantle is not uniform in composition. Instead, it evolves as continents drift apart and new seafloor is created. To better understand the role of hotspots in the creation of new seafloor and how the shallow mantle changes as the ocean basin matures, the International Ocean Discovery Program (IODP) Expeditions 391 and 397T drilled six different underwater volcanoes along the Walvis Ridge in the southern Atlantic Ocean. The Walvis Ridge consists of a line of underwater volcanoes formed by a hotspot during the separation of Africa from South American and the formation of the Southern Atlantic Ocean. Using core samples obtained at the six sites, this project will investigate three main questions. First, how much the upper mantle contributes to Walvis Ridge volcanism? What determines the proportion of upper mantle versus hotspot contribution to Walvis Ridge volcanism? Finally, how does the upper mantle change as the continents drift apart and the southern Atlantic Ocean expands. This project supports collaborations between US and international scientists. It will also fund undergraduate and graduate research by students traditionally underrepresented in geosciences (Native American, Black, LGBTQ, etc.).The overarching goal of this project seeks to better understand the magmatic processes associated with continental rifting and ocean basin formation in the South Atlantic, beginning in the early Cretaceous and continuing through today. To do this, IODP Expeditions 391 and 397T drilled six sites spanning 1200km and ~620m of basaltic basement along the Tristan-Gough-Walvis Ridge (TGW) hotspot track. The drill sites sample a significant spatial and temporal range along the TGW: one site on the Frio Rise (adjacent the African continent), two sites on the Valdivia Bank (cognate with the Rio Grande Rise and formed adjacent to the early mid-Atlantic Ridge), and three guyots on the “trident” that leads to the volcanic islands of Tristan da Cunha and Gough. In collaboration with other members of the science party, this project will conduct a comprehensive geochemical and geochronological study of recovered basaltic core to document the changing geodynamic interactions of the hotspot with the overlying lithosphere as rifting and seafloor spreading progressed. The team will collect a wealth of data, including geochronology (Duncan & Heaton, OSU), whole rock geochemistry (Nelson, TU; Potter & Shervais, USU), mineral and associated melt inclusion chemistry (Potter & Shervais, USU), noble gas abundances and isotopic signatures (Dygert & Scholpp, UTK), oxygen fugacity characterization of lavas (Dygert & Scholpp, UTK), and whole rock Re-Os isotopic compositions (Nelson, TU). The team will use these data to test three hypotheses based on preliminary work: (1) Lava chemistry will evolve geochemically from the Etendeka Large Igneous Province in the NE towards the intraplate oceanic islands of Gough and Tristan de Cunha to the SW, consistent with decreasing magma flux through time and changing melt sources; (2) Magmatic flux varies through time and is tied to the proximity to other geologic features (e.g. spreading ridge, African continent, etc.); and (3) Proximity to the spreading ridge will result in lavas with a higher proportion of MORB-like magma (DMM source) relative to the hotspot source. On a small scale, the high-quality core obtained at the various drilling sites provides a unique window into timing and geochemical variations within an individual seamount as it formed and how that may vary with proximity to the spreading ridge. On a larger scale, this work will provide an unmatched look at how plume-ridge interactions change over time.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.