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

合作研究：特里斯坦-高夫-沃尔维斯海岭热点系统的演化：391/397T 探险队火山基底的年龄和成分

• 批准号: 2317551
• 负责人: Robert Duncan
• 金额: $ 10.92万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-07-15 至 2025-06-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2317551&HistoricalAwards=false
• 关键词: Collaborative; Research; Evolution; Tristan; Gough

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.

热点是地幔中起源于核心-地幔边界附近的异常温暖区域，它们在板块构造中发挥着重要作用，是大陆分裂和随后随着大陆碎片漂移而形成新海洋的主要驱动因素之一。海洋在陆地之间形成，有影响力的热点持续存在，然后在新的海底形成一系列较小的火山喷发。然而，在某些情况下，浅地幔的成分并不均匀，而是随着大陆的漂移和新海底的形成而演化。随着海洋盆地的成熟，浅层地幔发生变化，国际海洋发现计划 (IODP) 391 和 397T 探险队沿着南大西洋的沃尔维斯海脊钻探了六座不同的水下火山。该项目将利用在六个地点获得的岩心样本，研究三个主要问题：第一，上地幔有多少。是什么决定了上地幔与热点对鲸湾岭火山活动的贡献比例？最后，随着大陆漂移和南大西洋扩张，上地幔如何变化？它还将资助传统上在地球科学领域代表性不足的学生（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大陆裂谷和洋盆相关的岩浆过程。为实现这一目标，IODP 探险队 391 和 397T 钻探了横跨 1200 公里和 1200 公里的六个地点。沿着 Tristan-Gough-Walvis Ridge (TGW) 热点轨道约 620m 的基底基底，钻探地点对 TGW 沿线的重要空间和时间范围进行了采样：一个地点位于弗里奥海隆（毗邻非洲大陆），两个地点位于弗里奥隆起（毗邻非洲大陆）。瓦尔迪维亚浅滩（与格兰德河隆起同源，毗邻早期大西洋中脊），以及通往火山岛的“三叉戟”上的三个居奥特里斯坦·达库尼亚和高夫与科学党的其他成员合作，该项目将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，热点与上覆岩石圈的地球动力学相互作用的变化。该团队将收集大量数据，包括地质年代学（Duncan & Heaton，OSU）、全岩地球化学（Nelson，TU；Potter & Shervais， USU）、矿物和相关熔体包裹体化学（Potter & Shervais，USU）、稀有气体丰度和同位素特征（Dygert & Scholpp，UTK）、熔岩的氧逸度表征（Dygert & Scholpp，UTK）以及全岩 Re-Os同位素组成（纳尔逊，TU）。该团队将使用这些数据来测试基于初步工作的三个假设：（1）熔岩化学将从地球化学上看，从东北部的埃滕德卡大型火成岩省向高夫岛和特里斯坦德库尼亚岛的板内海洋岛屿到西南部演化，与随时间推移岩浆通量减少和熔体来源变化一致；(2) 岩浆通量随时间变化，并与靠近其他地质特征（例如扩张脊、非洲大陆等）；以及 (3) 靠近扩张脊将导致熔岩中含有较高比例的 MORB 类岩浆。 （DMM源）相对于热点源，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，以及它如何随着接近程度而变化。在更大的范围内，这项工作将提供无与伦比的视角来了解羽流-山脊相互作用如何随时间变化。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查进行评估，被认为值得支持。标准。