Can Partial Melting of the Hydrous Intermediate-Basic Lower Continental Crust Generate C-type Adakites?——Comment on Zhang et al. (2012)

Dehydration melting of the intermediate-basic(SiO2=50%~60%) source undera pressure of 1.0~1.2 GPa(corresponding to 35~40 km depth) will generate high portion of plagioclase in the residuum,and the content of garnet in the residuum may not exceed 20% in most instances.Accordingly,the intermediate to acid melts,which are in equilibrium with such residuum,will not display the geochemical features of adakite.Meanwhile,the geochemical behavior of potassium in the partial melting system of K-rich sources does not obey the Henry's law of dilute solution,so the potassium content in the melt might be significantly overestimated by the calculation based on the assumption of the highly incompatible behaviour of potassium.