Assessing the role of the lithospheric mantle during passive margin development - insights from the South Atlantic African margin

评估岩石圈地幔在被动边缘发育过程中的作用 - 来自南大西洋非洲边缘的见解

• 批准号: 2305552
• 负责人: Tyrone Rooney
• 金额: $ 57.23万
• 依托单位: Michigan State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-01-01 至 2026-12-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2305552&HistoricalAwards=false
• 关键词: Assessing; role; lithospheric; mantle; during

Oceans and continents dominate the surface of Earth. Continental crust is thick and ancient, preserving billions of years of history. Oceanic crust is much younger. Plate tectonic processes bring together different continental plates into supercontinents. Supercontinents are then broken apart to form new oceans. This project focuses on the process of transition between continental and oceanic crust. We examine lava from the edge of a continent that has been rifted, and where an ocean has been newly created. These lavas can provide insight into how magmatism impacted the breakup process. The project focuses on the southwestern margin of the Atlantic Ocean along the coast of Angola. This region has been uplifted since the continent began to break apart. The uplift brings to the surface rocks that are usually buried under thick piles of sediment. Broader Impacts include support for undergraduate and graduate students to participate in research and training activities. The project will also create a module for use in undergraduate classes for non-science majors. The substantial hydrocarbon interests along the rifted margins of the South Atlantic have resulted in strong seismic characterization of basins along the continental margin. The seismic data provide an important interpretive framework that has recognized the presence of magmatism in the hyper-extended and supposedly ‘non-volcanic’ basins. Lavas and xenoliths, typically the most direct probe of mantle conditions at passive rifted margins, are usually buried under thick sediments. This project will obtain new petrographic, geochronologic, major and trace element, and isotopic data from volcanic rocks and xenoliths from the southern Angolan continental margin that are exposed due to uplift of the crust. This focus region provides an ideal venue to explore the transition between the richly volcanic margin that dominates further south in Namibia, and the vast sedimentary basins that define the margin further north in Angola. Analytical and interpretative aspects of the project are focused on two questions: 1) Why do basins in southern Angola exhibit the characteristics of a magma-poor volcanic margin (i.e., hyper-extended crust and thick sediment accumulation) but also experience magmatism? This question will be addressed by examining the isotopic, major and trace element characteristics of magmatism along the basin margin that is along strike with gravity highs associated with offshore magmatic features. Sub-lithosphere contributions to the lavas will be constrained using these data. 2) Is the Upper Cretaceous magmatic event in this region and synchronous African margin uplift the result of processes operating in the plate or underlying asthenosphere? This question will be addressed by examining lavas and associated mantle xenoliths that erupted along the African passive margin contemporaneous with this uplift event. The project will include an isotope study on lavas and xenoliths to explore possible source reservoirs, and a compositional study of minerals within the xenoliths. The outcome of this work could have substantial implications beyond the discipline given the importance of magmatism in influencing hydrocarbon systems along this passive rifted margin.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.

海洋和大陆主导着地球表面，海洋地壳具有数十亿年的历史，板块构造过程将不同的大陆板块聚集在一起，形成超级大陆。该项目的重点是大陆地壳和海洋地壳之间的过渡过程，我们研究裂谷的大陆边缘的熔岩，以及新形成的海洋。这些熔岩可以提供有关如何形成的见解。该项目的重点是安哥拉沿岸的大西洋西南边缘，自从大陆开始分裂以来，该地区的地表岩石就一直被抬升。更广泛的影响包括支持本科生和研究生参与研究和培训活动，该项目还将创建一个供非科学专业本科生使用的模块。结果地震数据提供了一个重要的解释框架，该框架已认识到超伸展和所谓的“非火山”盆地中存在岩浆作用，这通常是最直接的探测。被动裂谷边缘的地幔条件通常埋藏在沉积物厚层之下，该项目将从火山岩中获得新的岩石学、地质年代学、主量和微量元素以及同位素数据。由于地壳隆起而暴露的安哥拉南部大陆边缘的包体和捕虏体为探索纳米比亚南部的丰富火山边缘与界定边缘的巨大沉积盆地之间的过渡提供了理想的场所。该项目的分析和解释方面主要集中在两个问题：1）为什么安哥拉南部的盆地表现出贫岩浆火山边缘的特征。 （即超伸展的地壳和厚厚的沉积物堆积）还经历岩浆作用吗？这个问题将通过盆地边缘沿与近海岩浆特征相关的重力高点的岩浆作用的同位素、主量和微量元素特征来解决。使用这些数据，岩石圈下对熔岩的贡献将受到限制。 2) 该地区的上白垩统岩浆事件和同步的非洲边缘抬升是否是板块或底层作用过程的结果。这个问题将通过检查与这次隆起事件同时发生的非洲被动边缘喷发的熔岩和相关地幔捕虏体来解决。该项目将包括对熔岩和捕虏体进行同位素研究，以探索可能的源储层，并对矿物进行成分研究。鉴于岩浆作用在影响被动裂谷边缘碳氢化合物系统方面的重要性，这项工作的成果可能会产生超出学科范围的重大影响。通过使用基金会的智力价值和更广泛的影响审查标准进行评估，NSF 的法定使命被认为值得支持。