Melting of pelitic sediments at subarc depths: 2. Melt chemistry, viscosities and a parameterization of melt composition

The now numerous experimental studies on sediment melting at sub-arc pressures provide the data necessary to model melt compositions. These vary systematically as a function of melt fraction (F) to F=0.6. Compositional bands as a function of melt fraction are relatively narrow for all major oxides except for the alkalis where pressure and H2O-contents lead to variations by a factor of 3–5. Most sediment melts are meta- to slightly per-aluminous granites with 71–77wt.% SiO2 (on a volatile free basis), 12–16wt.% Al2O3, and 8–12wt.% total Na2O+K2O; MgO+FeO increase from 0.5 near the solidus to ~3.0wt.% at F=0.6, while CaO remains