Cooling of young Arctic oceanic lithosphere modulated by off-axis fluid circulation and post-glacial sedimentation

Mid-ocean ridges (MORs) are sites of key thermo-chemical transfers between the Earth's interior and the ocean. Heat flow at MORs primarily depends on lithospheric age but is also modulated by various processes including sedimentation, hydrothermal activity, and faulting, which alter the thermal properties of young oceanic lithosphere. Here we quantify this modulation by analyzing heat flow measurements across the ultraslow-spreading Mohn’s Ridge in the Arctic Ocean. The Mohn’s ridge features major asymmetries in tectonic structures, with larger-offset normal faulting occurring on the West side (North American plate), as well as more sedimentation on the East side (Eurasian plate).

Recently acquired measurements of conductive heat flow across Mohn’s Ridge reveal a significant asymmetry. The eastern (sedimented) side shows a typical conductive profile with values exceeding 600 mW/m² at the axis decreasing off-axis towards an asymptote at ~100 mW/m². By contrast, the western (faulted) side lacks this conductive plateau, with conductive heat flow dropping to near zero off-axis in ~15-Ma seafloor.

We used 2-D numerical models of hydrothermal convection coupled with conductive heat transport to test two hypotheses (1) An asymmetry in the intensity of brittle deformation leads to greater crustal permeability on the faulted west side, enabling cooling by hydrothermal circulation far off-axis. This manifests as very low conductive heat flux in 10+Ma seafloor. (2) Permeability is the same on both sides of the ridge, but a thick, impermeable sediment blanket suppresses off-axis hydrothermal convection in the Eurasian plate to the East. We find that explaining the low Western heat fluxes requires a high off-axis permeability. The Eastern heat fluxes are better explained either by a lower permeability, or the insulating effect of the sediment. Interestingly, the instantaneous addition of a sediment blanket at a prescribed time in our simulations can turn a heat flow profile typical of the West side into a classical conductive profile typical of the East side in a few 100 kyrs. This suggests that a post-glacial input of sediment on the Eurasian plate could have contributed to a rapid onset of the heat flow asymmetry across Mohn’s Ridge.