The Buoyancy of Cratonic Lithospheric Mantle

Abstract Cratons are generally thought to be characterized by stable, long‐lived mantle roots. However, recent studies have suggested that the lithospheric mantle may be prone to removal, implying that it may be denser than the asthenosphere. To address these suggestions, we use a global data set of mantle xenoliths to estimate the density structure of the cratonic lithospheric mantle (CLM), which we then compare with the density of the asthenospheric mantle at equivalent depths. Most of the CLM is either neutrally buoyant or slightly positively buoyant relative to the asthenosphere. The exception is where pyroxenite has accumulated due to melt infiltration. For these pyroxenites to remain within the CLM over geologically significant timescales they must be relatively small, that is, ≤1–20 km in size for a CLM viscosity of 10 21 –10 23 Pa·s. Our results suggest that the majority of cratonic lithospheric roots are long‐lived due to their neutral‐to‐positive buoyancy.