An Experimental Melting-crystallization Study on Basalt at High Pressures

A series of melting-crystallization experiments on alkali basalt samples from Minqing,Fujian Prov-ince was carried out in dry and water-bearing systems at high pressures.A high-pressure melting curve was obtained.The results indicate that clinopyroxene crystallized from basalt melt at 13.5-23.7kbar,spinel at 23.7-28.6kbar and garnet at>28.6kbar.With increasing pressure,the CaSiO3 contents of clinopyroxenes increase;and the FeSiO3 decreases,but the chemical composition of garnet does not show any significant difference.The minerals are larger and euhedral in the wa-ter-bearing system.Therefore,we consider that natural megacrysts of the basalt can crystallize from the water-bearing basalt magma at high pressure.So the megacysts may be derived from the upper mantle as a result of magmatic crystallization-fractionation under high pressure.

A series of melting-crystallization experiments on alkali basalt samples from Minqing, Fujian Prov- ince was carried out in dry and water-bearing systems at high pressures. A high-pressure melting curve was obtained. The results indicate that clinopyroxene crystallized from basalt melt at 13.5-23.7 kbar, spinel at 23.7-28.6 kbar and garnet at >28.6 kbar. With increasing pressure, the CaSiO_3 contents of clinopyroxenes increase; and the FeSiO_3 decreases, but the chemical composition of garnet does not show any significant difference. The minerals are larger and euhedral in the wa- ter-bearing system. Therefore, we consider that natural megacrysts of the basalt can crystallize from the water-bearing basalt magma at high pressure. So the megacrysts may be derived from the upper mantle as a result of magmatic crystallization-fractionation under high pressure.