How warm are passive continental margins? A 3-D lithosphere-scale study from the Norwegian margin

We model the three-dimensional (3-D) conductive thermal field of the Norwegian margin and evaluate its lithospheric configuration, which is consistent with two independent observables: temperature and gravity. Here, we show that knowledge of the sediment and crustal configuration of the passive continental margin provides constraints for the configuration and thermal structure of the lithosphere. We find that the thickness of the oceanic lithosphere adjacent to the stretched continental margin controls, to a large degree, the shallow conductive thermal field of the entire margin. Our results confirm estimates of lithospheric thickness from seismology but contradict estimates from cooling models, which assume an equilibrium thickness of the oceanic lithosphere of 125 km. We find that the crust is colder in the oceanic than in the continental domain, whereas this trend is reversed downward. We obtain lateral temperature differences of similar to 100 degrees C at 5 km depth across the margin that increase to similar to 400 degrees C at 50 km depth. Higher temperatures and heat flows for the oceanic lithospheric mantle compared to the continent indicate that reduced upper-mantle P-wave velocities and densities are thermally induced.