Fractionation of zirconium and hafnium during processes of mantle metasomatism

Resumo

For the first time, fractionation of zirconium and hafnium in carbonatized mantle xenoliths from the eastern Antarctic has been studied. An elevation relative to the chondrite values of Zr/Hf in the metasomatized xenoliths has been revealed. The main reactions of the carbonate metasomatism lead to replacement of primary orthopyroxene by secondary clinopyroxene. A substantial broadening of the clinopyroxene crystallization field results in an increase of Zr/Hf in an equilibrated melt due to a higher partition coefficient of Hf in clinopyroxene, relative to that of Zr. Migration of reaction-active carbonate and carbonate–silicate melts, equilibrated to metasomatic wehrlite, causes an increase in the Zr/Hf value in the carbonatized mantle substrate.