NSF Award
2305552
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. <br/><br/>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.<br/><br/>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.
