汉诺坝玄武岩化学及其演化趋势

汉诺坝玄武岩于中新世喷出。除了碱性玄武岩以外,夏威夷岩广泛分布,还有苦橄玄武岩和马盖尔岩。有三个岩浆演化趋势:地壳岩浆房内橄榄石和单斜辉石斑晶组合的分离作用产生了从夏威夷岩到马盖尔岩的肯尼迪分异趋势;莫霍面附近的岩浆房内石榴石、普通辉石、歪长石和钛铁矿巨晶组合的分离作用导致了由原生夏威夷岩和碱性玄武岩经过进化的夏威夷岩和碱性玄武岩到拉斑玄武岩的跨式B型分异趋势;原生岩浆演化趋势。

THE CHEMISTRY OF HANNUOBA BASALTS ANDTHEIR TRENDS OF MAGMATIC EVOLUTION

The Hannuoba basalts were erupted in Miocene. Among them the hawaiites covers a large area and also picrite-basalts and mugearites occur. Most of the Hannuoba basalts belong to alkali olivine basalt series, while a small amount of them belong to tholeiite series.Three chemical trends of magma evolution have been suggested. The Kennedy trend of differentiation from hawaiite to mugearite has been resulted from fractionation of a phenoeryst assemblege of olivine and clinopyroxene in the magma reservior in the upper crust. The straddle-B type trend of differentiation from primary hawaiite and alkali basalt through hawaiite and alkali basalt to tholeiitic basalt has been formed under the control of fraetionation of a megacryst assemblege of garnet, augite, anorthoclase and ilmenite in a magma reservior near the Moho. A new chemical trend of primary magma is suggested. The new trend from primary hawaiite through primary alkali basalt to primary picrite-basalt is resulted from the increase in the degree of partial melting of upper mantle peridotites.