Widespread basalt enrichment within the continental lithospheric mantle

In comparison with oceans, continents are generally difficult to subduct due to the buoyancy of their crust. However, the density structure of the continental lithospheric mantle (CLM) and its effect in the stability of continents remains unclear. Here, we employed geodynamic models based on data assimilation to constrain the density structure of CLM. We first conducted a systematic analytical calculation using diverse observations including topography, heat flow, seafloor age, as well as seismic data to infer the density structure of both continental and oceanic lithosphere. By incorporating contributions from both the convective mantle and the lithosphere using topography, geoid and the model’s consistency with geological constraints, we updated the CLM’s density structure. Our results show that the CLM is consistently denser than the asthenosphere, where the non-cratonic CLM is denser than the cratonic CLM. The average density anomaly of the cratonic CLM is about 1 % while the that of the non-craton CLM can reach 3 %. By quantifying the geochemical compositions of the CLM using thermodynamic calculations, we find that an enrichment of 20wt% basalt can produce a density anomaly of 1% while 50wt% of basalt enrichment produces 3% excess density. We conclude that the CLM is widely enriched in basaltic composition. This implies that the CLM is less gravitational stable than traditionally thought and may actively participate in mantle convection.