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

海洋和大陆主宰着地球的表面。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组合成超级大陆。然后，超级大陆分裂成新的海洋。该项目的重点是大陆地壳和大洋地壳之间的过渡过程。我们研究了来自大陆边缘的熔岩，该大陆已经断裂，并且新形成了海洋。这些熔岩可以提供深入了解岩浆活动如何影响解体过程。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，这个地区一直在隆起。隆起将通常埋在厚厚的沉积物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加研究和培训活动。该项目还将创建一个模块，用于非科学专业的本科课程。南大西洋断裂边缘沿着有大量的油气资源，因此，沿着大陆边缘的盆地具有强烈的地震特征。地震数据提供了一个重要的解释框架，已经认识到在超扩展和所谓的“非火山”盆地的岩浆活动的存在。熔岩和捕虏体通常埋藏在厚的沉积物之下，是被动裂谷边缘地幔条件最直接的探针。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相学、地质年代学、主要元素和微量元素以及同位素数据。这一重点区域提供了一个理想的场所，探索丰富的火山边缘之间的过渡，占主导地位的进一步南部在纳米比亚，和巨大的沉积盆地，界定边缘进一步北部在安哥拉。该项目的分析和解释方面集中在两个问题上：1）为什么安哥拉南部的盆地表现出岩浆贫乏的火山边缘特征（即，超伸展地壳和厚沉积物堆积），但也经历岩浆活动？这个问题将通过研究同位素，主要和微量元素特征的岩浆沿着盆地边缘，是沿着走向与重力高与近海岩浆特征。岩石圈下的熔岩的贡献将受到限制，使用这些数据。2)该地区晚白垩世岩浆事件和非洲大陆边缘的同步隆升是板块或下伏软流圈作用的结果吗？这个问题将通过研究与这次隆升事件同时发生的沿着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，并对捕虏体中的矿物进行成分研究。这项工作的结果可能会有实质性的影响超出了学科的重要性，岩浆作用在影响油气系统沿着这被动裂谷margin.This奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

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.