The effect of melt segregation on polybaric mantle melting: Estimation from the incremental melting experiments

Abstract

For understanding mantle melting processes, incremental batch melting of peridotite was experimentally investigated. The experiments simulated partial melting of a mantle with 1344°C potential temperature upon adiabatic decompression, which segregates melt increments at 2, 1.5, 1 and 0.5 GPa. The compositions of incremental melts formed at respective pressures were obtained using `diamond aggregates method'. Mass balance calculations show that they are 4.9–6.5 wt.% partial melts in each experiment and that the mantle melts 21.0 wt.% by decompression to 0.5 GPa. Comparison with batch melting experiments on the same lherzolite provides an estimation of the effects of melt segregation on polybaric mantle melting. It was clearly demonstrated that melt removal from the melting system reduces the amount of melt produced. To form a certain thickness of oceanic crust at ridges by near fractional mantle melting, a potential temperature several tens of degrees higher than that for batch melting is required. The compositions of incremental melts are characterized by high FeO * and MgO and low TiO 2, Al 2O 3 and Na 2O contents compared to those of batch melts. On the other hand, the aggregates of melt increments are similar in composition to batch melts. Both incremental melting and batch melting can thus produce a melt with similar major element composition from the identical source lherzolite, but a higher potential temperature is required for batch melting.