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

Melting experiments involving fifteen runs were performed at pressures betw een 1.0 and 2.0 GPa in order to locate the liquidus temperatures, the solid us temperatures, and the melting intervals of the Wannienta basaltic magma, northern Taiwan. The experimental results showed that the liquidus and sol idus temperatures were raised by 60 GPa and 40 GPa respectively. The liquid us mineral at 1.0 GPa is orthopyroxene, whereas the liquidus mineral is cli nopyroxene at 1.5 and 2.0 GPa. The crystallized phases are clinopyroxene an d plagioclase at temperatures between 1220 and 1270 degrees C and pressures between 1.0 and 2.0 GPa. Garnet appears at 2.0 GPa near the solidus. The g eochemical 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 e nriched with decreasing temperature while depletions occur in Mg, Ca, and N a. 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 crystalli zation of the Wannienta basaltic magma to produce andesites could be modele d at low pressure. The fractionates involved included iron-titanium oxides, olivine, plagioclase, and clinopyroxene. (C) 2000 Elsevier Science Ltd. Al l rights reserved.