Thermodynamic modelling of melting in chemically heterogenous mixtures of peridotite and pyroxenite

Melting of pyroxenite veins or layers has been proposed as an explanation for the 'garnet signature' in MORB and for characteristic source signatures in OIB. Recent experiments have constrained the melt productivity of respresentative pyroxenite compositions but pyroxenite melting in the convecting mantle will be enhanced by heat transfer from the surrounding peridotite. The algorithm DUAL ADIABA T is based on the MELTS software package. - It calculates isentropic decompression paths for two lithologies that are in thermal but not chemical equilibrium. We have used DUAL_ADIABAT to compare the melting of variable proportions of pyroxenite and peridotite along typical mantle adiabats with and without chemical equilibrium between the systems. The effects of melt extraction, homogenisation and transport processes and melt-region geometry may be tested.