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表面。大陆地壳厚重而古老，保存着数十亿年的历史。洋壳要年轻得多。板块构造过程将不同的大陆板块汇聚成超大陆。然后，超级大陆被分裂，形成新的海洋。这个项目的重点是大陆地壳和海洋地壳之间的过渡过程。我们检查了一块大陆边缘的熔岩，这块大陆已经裂解，在那里新形成了一片海洋。这些熔岩可以洞察岩浆活动是如何影响破裂过程的。该项目的重点是沿安哥拉海岸的大西洋西南部边缘。自从大陆开始分裂以来，这一地区一直在隆起。抬升带来了地表岩石，这些岩石通常埋在厚厚的沉淀物堆下。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，用于非理科专业的本科生课堂。南大西洋裂谷边缘的大量油气权益导致大陆边缘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，它确认了超伸展和被认为是“非火山”盆地中岩浆作用的存在。熔岩和包体通常是对被动裂谷边缘地幔条件最直接的探测，通常埋藏在厚厚的沉积物下。该项目将从安哥拉南部大陆边缘因地壳抬升而暴露的火山岩和捕虏体中获得新的岩石学、地质年代学、常量元素和微量元素以及同位素数据。这一重点区域为探索纳米比亚更南边的丰富火山边缘和安哥拉更北边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侧重于两个问题：1)为什么安哥拉南部的盆地表现出缺乏岩浆的火山边缘的特征(即，超伸展的地壳和厚厚的沉积物堆积)，但也经历了岩浆作用？这个问题将通过研究沿盆地边缘的岩浆活动的同位素、主要元素和微量元素特征来解决，这些特征是沿着与近海岩浆特征有关的走向和重力高。利用这些数据，次岩石圈对熔岩的贡献将受到限制。2)该地区上白垩统的岩浆事件和非洲边缘的同步抬升是板块或软流圈下伏过程的结果？这个问题将通过研究与这次隆升事件同时沿非洲被动边缘喷发的熔岩和相关的地幔捕虏体来解决。该项目将包括一项关于熔岩和包体的同位素研究，以探索可能的生油层，以及包体内矿物的成分研究。考虑到岩浆作用在影响沿被动裂谷边缘的碳氢化合物系统方面的重要性，这项工作的结果可能会产生超出学科范围的重大影响。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.