Melting experiment of a Wannienta basalt in the Kuanyinshan area,northern Taiwan,at pressures up to 2.0 GPa

Melting experiments involving fifteen runs were performed at pressures between 1.0 and 2.0 GPa in order to locate the liquidus temperatures, the solidus temperatures, and the melting intervals of the Wannienta basaltic magma, northern Taiwan. The experimental results showed that the liquidus and solidus temperatures were raised by 60 GPa and 40 GPa respectively. The liquidus mineral at 1.0 GPa is orthopyroxene, whereas the liquidus mineral is clinopyroxene at 1.5 and 2.0 GPa. The crystallized phases are clinopyroxene and plagioclase at temperatures between 1220 and 1270°C and pressures between 1.0 and 2.0 GPa. Garnet appears at 2.0 GPa near the solidus. The geochemical evolution of the residual magma with decreasing temperature show the following trends: At 1.0 GPa, Al, Na, and K are progressively enriched while depletions occur in Mg. At 2.0 GPa, Si, Fe and K are progressively enriched with decreasing temperature while depletions occur in Mg, Ca, and Na. The fractionation trend of the Kuanyinshan volcanic series is similar to the trend observed in residual magmas at pressures between one atmosphere and 1.0 GPa. These results indicate that the depth for fractional crystallization of the Wannienta basaltic magma to produce andesites could be modeled at low pressure. The fractionates involved included iron-titanium oxides, olivine, plagioclase, and clinopyroxene.