Interplay between fluid flow, serpentinisation and deformation mode at ultra-slow spreading centres

The polar and subpolar mid-ocean ridges (MOR) form a unique seafloor environment. These ridges belong to the melt-starved ultraslow spreading ridges where seafloor spreading works differently from any faster spreading ridge. Abundant deep-sea life, higher incidence of hydrothermal plumes and signs for mantle rock alteration in contact with water at depths of 15 km suggest an intensive interaction between seawater and lithosphere and possibly a large flux of heat and matter into the ocean. These regions exhibit ridge portions where mantle rocks are directly exposed in a deep rift valley. Alteration of these mantle rocks to serpentinite releases heat and reduced compounds (e.g., H2, CH4, Fe) into the ocean and drastically lowers the shear strength of the lithosphere. As a result, the lithosphere deforms in an entirely different way from faster spreading ridges. The distribution of serpentinite, however, is not well understood. Serpentinite may be concentrated on large shear zones that act as major fluid pathways or fluids may percolate far more pervasively through cracks in the lithosphere and may be facilitated by permeability generated by serpentinisation reactions.

The postdoctoral researcher will form part of a multidisciplinary project formed by scientists at MARUM and AWI focused on understanding interactions between deformation, fluid flow and serpentinisation. This postdoctoral position will be dedicated to use and develop numerical models to understand the distribution of serpentinite versus magmatic material at ultra-slow spreading ridges and how it relates to the interpreted deformation modes in these environments. The current available numerical models include visco-elasto-plastic rheologies, serpentinisation and melting. The main task of the postdoctoral researcher will be to include a module to use thermodynamic constraints on petrological transformations to obtain seismic velocities along the numerically modelled section. The numerically modelled section velocities will then be compared to wide-angle seismic velocities at ultra-slow spreading ridges and used to better constrain the relationship between mantle serpentinisation, magmatism and deformation.