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: 2317553
• 负责人: Katherine Potter
• 金额: $ 17.36万
• 依托单位: Utah 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=2317553&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.

热点是地幔中异常温暖的区域，起源于地核-地幔边界附近。它们在板块构造中扮演着重要的角色，是大陆分裂和随后形成新海洋的主要驱动力之一。随着大陆碎片漂移，新的海洋在大陆块之间形成，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。这些喷发取样于深部热点，在某些情况下，取样于浅层地幔。然而，浅层地幔的成分并不均匀。相反，它是随着大陆的分离和新海底的形成而进化的。为了更好地了解热点在新海底形成中的作用，以及随着海洋盆地的成熟，浅层地幔是如何变化的，国际海洋发现计划（IODP）第391和397T探险队沿着南大西洋沃尔维斯山脊钻探了六个不同的水下火山。沃尔维斯海岭由一系列水下火山组成，这些火山是在非洲与南美洲分离和南大西洋形成期间由一个热点形成的。利用在六个地点获得的岩心样本，该项目将调查三个主要问题。首先，上地幔对沃尔维斯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领域代表性不足的学生（印第安人、黑人、LGBTQ等）的本科和研究生研究。该项目的首要目标是更好地了解从白垩纪早期开始一直持续到今天，与南大西洋大陆裂谷和海洋盆地形成有关的岩浆过程。为此，IODP探险队391和397T沿着Tristan-Gough-Walvis Ridge （TGW）热点轨道钻探了6个地点，跨越1200公里和约620米的玄武岩基底。这些钻探地点在TGW沿线具有显著的时空范围：一个地点位于弗里奥隆起（毗邻非洲大陆），两个地点位于瓦尔迪维亚河岸（与里约热内卢大隆起同源，形成于早期大西洋中脊附近），三个地点位于通往特里斯坦达库尼亚和戈夫火山岛的“三叉戟”上。该项目将与科学小组的其他成员合作，对回收的玄武岩岩芯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。该团队将收集丰富的数据，包括地质年代学（Duncan & Heaton， OSU），整个岩石地球化学（Nelson， TU; Potter & Shervais， USU），矿物和相关的熔融包裹体化学（Potter & Shervais， USU），稀有气体丰度和同位素特征（Dygert & Scholpp， UTK），熔岩的氧逸度特征（Dygert & Scholpp， UTK），以及整个岩石的Re-Os同位素组成（Nelson， TU）。研究小组将利用这些数据来验证基于初步工作的三个假设：(1)熔岩化学将从东北的Etendeka大火成岩省向Gough和Tristan de Cunha的板内海洋岛屿向西南演变，与岩浆通量随时间减少和熔体来源变化相一致；(2)岩浆通量随时间变化，并与邻近其他地质特征（如伸展脊、非洲大陆等）有关；(3)靠近扩张脊的熔岩相对于热点源具有较高的MORB-like岩浆（DMM源）比例。在小范围内，在各个钻井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，以及它如何随着靠近伸展脊而变化。在更大的范围内，这项工作将提供一个无与伦比的关于羽状脊相互作用如何随时间变化的研究。该奖项反映了美国国家科学基金会的法定使命，并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，被认为值得支持。