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

海洋和大陆占据了地球表面。大陆地壳厚而古老，保存了数十亿年的历史。海洋地壳要年轻得多。板块构造过程将不同的大陆板块汇聚成超级大陆。然后超级大陆分裂形成新的海洋。本项目主要研究大陆地壳与海洋地壳的过渡过程。我们研究了大陆边缘被撕裂的熔岩，以及新形成的海洋。这些熔岩可以让我们深入了解岩浆作用是如何影响分裂过程的。该项目的重点是沿着安哥拉海岸的大西洋西南边缘。自从大陆开始分裂以来，这个地区一直在抬升。隆起把通常埋在厚厚的沉积物堆下的岩石带到了地表。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模块，用于非科学专业的本科课程。南大西洋裂谷边缘的大量油气资源导致了大陆边缘盆地的强烈地震特征。地震资料提供了一个重要的解释框架，确认了超伸展和所谓的“非火山”盆地中岩浆活动的存在。岩浆和捕虏体通常被埋在厚厚的沉积物下，是被动裂陷边缘最直接的地幔条件探测工具。该项目将从安哥拉南部大陆边缘因地壳隆起而暴露的火山岩和捕虏体中获得新的岩石学、地质年代学、主要元素和微量元素以及同位素数据。这个重点区域为探索纳米比亚南部丰富的火山边缘和安哥拉北部广阔的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上：1)为什么安哥拉南部的盆地表现出岩浆匮乏的火山边缘特征（即超伸展地壳和厚沉积物堆积），但也经历了岩浆活动？这一问题将通过研究盆地边缘沿重力高走向的岩浆活动的同位素、主量元素和微量元素特征来解决。这些数据将限制亚岩石圈对熔岩的贡献。2)该地区的上白垩世岩浆事件和同步非洲边缘隆起是否是板块或下伏软流圈作用过程的结果？这个问题将通过研究与这次隆起事件同时期沿着非洲被动边缘喷发的熔岩和相关的地幔包体来解决。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，并对捕虏体内的矿物进行成分研究。鉴于岩浆作用在影响被动裂谷边缘油气系统中的重要性，这项工作的结果可能具有超越学科的重大意义。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。

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.