A decompression melting model for mantle with potential temperature (T_p) of 1300, 1400 and 1500 °C. The mantle has an adiabatic gradient of 0·3 °C km^–1 (Turcotte & Schubert, 1982) until it crosses the dry solidus and cools at a faster rate, producing melt at 0·4 % km^–1 (Klein & Langmuir, 1987). Decompression and melting stop at the base of the lithosphere. The dry mantle solidus and the solidus of mantle with 0·05 wt.% water are from Katz et al. (2003), and the depth of the transition from spinel- to garnet-lherzolite is from Klemme & O’Neill (2000).