Experimental Study on the genesis of flood basalt magma

在高压熔融实验的基础上，评价了复合羽流模型作为大陆洪泛玄武岩的来源。对MORB的组成进行了熔融实验，认为它代表了海洋地壳的平均组成，含有约9wt %的MgO。高压实验在2 Gpa以下用活塞缸试验装置进行，在2 Gpa以上用本基金设计制造的多砧试验装置进行。在单大气压熔融实验的基础上，排除低压分馏结晶分异的影响，估算了德干洪水玄武岩原始岩浆的组成。根据本研究确定的元素分配数据，认为原始岩浆不可能来源于地幔橄榄岩的部分熔融。结果表明，由古洋壳幔橄榄岩组成的复合羽流部分熔体的主微量元素组成与大陆洪泛玄武岩相一致。结合对复合地幔柱上升过程的计算机模拟，得出了含10%洋壳的复合地幔柱在3 Gpa压力下部分熔融产生德干洪水玄武岩岩浆的结论。其他省份的大陆洪泛玄武岩和某些洋岛玄武岩也有类似的结论。

The purpose of the present study is to evaluate the composite-plume model as a source material for continental flood basalt based on the melting experiments at high pressure. Melting experiments have been performed on the composition of MORB which is believed to represent averaged composition of oceanic crust, containing about 9 wt % of MgO. High pressure experiments were done by piston cylinder apparatus at pressure below 2 Gpa, and by multi-anvil apparatus, which was designed and built through this grant, above 2 Gpa. Based on the melting experiments at one atmosphere, composition of pristine magma of Deccan flood basalts was estimated eliminating the effects of low pressure fractional crystallization differentiation. It was concluded that the pristine magma could not be derived from any partial melt of mantle peridotite based on the elemental partitioning data determined through this study. It was shown that the expected major and trace element composition of partial melts of the composite plume, which is composed of the ancient oceanic crust and mantle peridotite, is consistent with the continental flood basalts. Combining the computer simulation on the ascent of the composite plume, it was concluded that the composite plume containing 10 % of oceanic crust can produce Deccan flood basalts magma by partial melting at pressure of 3 Gpa. It is also suggested that similar arguments are applicable for the continental flood basalts in other provinces and for some ocean island basalts.