Abstract

The lavas of the Hawaiian Islands range from mafic picrite-basalts and melilite-nepheline basalts to salic trachytes. Olivine basalt, by far the most abundant type, is regarded as representing the parent magma of the Hawaiian province. Closely associated with the olivine basalts are basalts, and picrite-basalts with many large phenocrysts of olivine. Further differentiation results in eruption of andesine andesite, oligoclase andesite, picritebasalt with abundant large augite phenocrysts, and more rarely trachyte. Following a long period of quiescence there have been erupted on some islands nepheline basanite, nepheline basalt, melilite-nepheline basalt, “linosaite,” and a third type of picrite-basalt. The mineral and chemical composition of the various rock types, and their distribution on the individual islands, are described.

Starting with olivine basalt as the parent magma means of deriving the other rock types are considered. It is concluded that crystal differentiation has been the principal process, although assimilation of limestone may also have been important. The parts played by gaseous transfer and selective remelting are difficult to evaluate, though both probably operated to some extent.

Comparison of the types of igneous rocks in the Hawaiian province with those recorded from other Pacific islands shows that the rocks throughout the true Pacific Basin are, for the most part, closely similar, and suggests essential uniformity of parent magma and petrogenic processes throughout the Pacific Basin.

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