A possible high Nb/Ta reservoir in the continental lithospheric mantle and consequences on the global Nb budget - Evidence from continental basalts from Central Germany

Our results suggest that the lithospheric mantle may host some of the “missing Nb”, but high-Nb/Ta domains are likely restricted to regions that have been affected by carbonatite metasomatism. Although Nb concentrations can be extremely high in carbonatites, such domains are probably a more local phenomenon and volumetrically too small to account as a whole for the global Nb deficit. Model calculations, however, indicate, that up to ∼30% of the “missing Nb” may be hosted in the subcontinental lithospheric mantle. The Earth's core or any other hidden reservoir in the deep mantle remains significant in balancing the global Nb budget, but their role may be less important than previously thought.