Hydrous origin of the continental cratonic mantle

We performed melting experiments of hydrous pyrolite at pressures from 3 to 8 GPa and temperatures from 1,100°C to 1,800°C to identify the origin of chemical variation in cratonic garnet peridotites with high contents of magnesian orthopyroxene. In hydrous conditions, the stability field of residual orthopyroxene expands relative to olivine above solidus, and the harzburgitic residue contains large amounts of Mg-rich (Mg# > 0.92) orthopyroxene at 4.5 to 6 GPa. The residual chemistry obtained from our experiments indicates that the chemical variation of the cratonic garnet peridotites possibly reflects formation by melt depletion under various water contents from almost anhydrous to a maximum of approximately 1% to 2% in the upper mantle at depths of about 100 to 200 km.