Partial melting experiments on peridotite and origin of mid-ocean ridge basalt

Recent partial melting experiments on peridotite indicate that mantle perid otites with Mg# < 88 can produce primitive mid-ocean ridge basalt by 15-25% partial melting at 1.0-1.5 GPa followed by small amounts (a few to 10%) of olivine fractionation, whereas those with Mg# > 89 can produce primitive m id-ocean ridge basalt by partial melting at pressures greater than 1.5 GPa followed by extensive olivine fractionation. Polybaric incremental batch me lting or stepwise fractional melting experiments indicate that the composit ions of accumulated incremental melts formed along a mantle adiabat in the pressure range 2.0-1.0 and 2.0-0.5 GPa are close to, but slightly more oliv ine-rich than, those of primitive mid-ocean ridge basalt, and that the amou nt of accumulated incremental melts is significantly smaller than that of b atch partial melts formed for the same potential temperature. The melting i n adiabatically ascending mantle beneath mid-ocean ridges would cease at de pths > 15 km because of the inflection of the solidus of mantle peridotite.