The rupture of continents and the formation of new ocean basins are perhaps the most dramatic phenomena in global tectonics but these processes are rarely shown in text book cartoons of the plate tectonic and biogeochemical cycles (e.g., Kelemen & Manning, 2015). Continental break-up is commonly associated with the impact on the lithosphere of mantle plumes and/or rifting. This leads to different styles of ocean-continent transitions, even along the same continental margin. For example, there are abundant volcanic flows and intrusions along the Greenland and Norwegian margins of the North Atlantic, whereas to the south, serpentinised rocks from the upper mantle are exposed on both the Galician and Newfoundland margins where volcanism is absent. CO2 (and CH4) is released in volcanic eruptions and during the contact metamorphism of organic-bearing sediments, but CO2 is also drawn down through the rapid intense weathering of fresh young volcanic rocks both on-land and after submergence following rifting. Similarly, upper mantle rocks react strongly with crustal fluids when exposed and seafloor serpentinites are commonly highly hydrated, oxidized and carbonated. To date, these fluid-rock reactions have not been considered in detail or quantified for input into the global carbon cycle.
The project will integrate geological and geophysical information from the margins of the north Atlantic Ocean to review styles of rifting and volcanism. This will provide context for detailed studies of volcanic and non-volcanic rifted margins on both sides of the Atlantic that have been sampled by scientific ocean drilling. Core logging coupled with whole rock and mineral analyses will determine the extent and relative timing of fluid-rock reactions and geochemical exchanges, including the carbon-uptake in veins or breccia cements, versus the draw-down through weathering reactions. Mineralogy coupled with stable oxygen and carbon and radiogenic strontium isotope analysis will provide information on fluid-rock reaction conditions and fluid compositions (e.g., Coggon et al., 2010). Absolute dates of secondary mineral formation will be determined by U-Pb, Rb-Sr LA-MC-ICP-MS approaches at Southampton or Ar-Ar with SUERC and/or international colleagues. Although carbon is the focus of this project, it will also yield information on a range of essential geochemical tracers of past Earth systems (e.g., seawater Mg/Ca).
Through comparison with other rifted margins the project will develop a numerical model underpinned by plate tectonic reconstructions to characterize the impacts of these processes on the carbon and other cycles and the interdependencies between rifting, volcanism and other parts of the global tectonic cycle.
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted by the School of Ocean & Earth Science and the Graduate School of the National Oceanography Centre Southampton. Specific training will include:
- Specialist training in quantitative drill core logging and description;
- Training in state of the art geochemical techniques, including sample preparation, trace element analysis by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and isotope analyses via Thermal Ionization Mass Spectrometry (TIMS) and Multi-collector ICP-MS and other techniques;
- Training in modelling using Bayesian networks to test the complex interdependencies between rifting, volcanism and weathering.
Please see https://inspire-dtp.ac.uk/how-apply for details.
Gernon et al., 2021 Global chemical weathering dominated by continental arcs since the mid-Palaeozoic, Nature Geoscience, doi.org/10.1038/s41561-021-00806-0
Coggon et al., 2010, Reconstructing Past Seawater Mg/Ca and Sr/Ca from Mid-Ocean Ridge Flank Calcium Carbonate Veins, Science 327,1114; doi: 10.1126/science.1182252
Kelemen and Manning, 2015, Reevaluating carbon fluxes in subduction zones, what goes down mostly comes up, Proc. NAS, doi/10.1073/pnas.1507889112