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G. A. Macdonald

Publications and source records attributed to G. A. Macdonald.

9 recordsLinked to original sources
USGS1968

A further contribution to the petrology of Haleakala volcano, Hawaii

Sixteen new chemical analyses of the later rocks of Haleakala Volcano , on the island of Maui, Hawaii , add to the differentiation picture for that volcano . The early rocks of the volcano are tholeiitic. These are followed by dominant hawaiites with less abundant alkalic olivine basalts, picrite-basalts of ankaramite type, and a few mugearites. Still later rocks, separated from earlier ones by a profound erosional unconformity, include some hawaiites and ankaramites, but are dominantly alkalic olivine basalts (basanitoids) containing as much as 16.5 percent normative nepheline, some of them transitional to ankaramite. The progression toward ultramafic, strongly undersaturated rocks (nephelinites), characteristic of the post-erosional lavas of other Hawaiian volcanoes, appears to have just begun at Haleakala .

Hawaii↗
USGS1949

Hawaiian petrographic province

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.

Hawaii↗
USGS1948

Petrography of Iwo Jima

The rocks of Iwo Jima are augite and augite-hornblende trachyandesites, distinctly more alkalic than the ordinary andesites of Japanese volcanoes or the average world andesite. They are described, and chemical analyses are listed. Fumarolic gases have altered some rocks to a mixture of opal and clay minerals and have cemented tuff with opal, calcite, zeolite, and iron oxides.

Iwo Jima↗
USGS1946

Contribution to the petrography of Haleakala Volcano, Hawaii

The volcanic rocks of Haleakala Volcano comprise, from oldest to youngest, the Honomanu, Kula, and Hana volcanic series. The Honomanu volcanic series consists largely of olivine basalt, with less abundant basalt and picrite-basalt containing large phenocrysts of olivine. In the Kula and Hana volcanic series there are some basalts and olivine basalts, but the characteristic rocks are andesites and picrite-basalt containing abundant phenocrysts of augite as well as olivine. New chemical analyses of six specimens of Kula lavas are given. Five are andesites, and one a picrite-basalt. Each of the six rocks is described in detail. A variation diagram for Haleakala rocks illustrates the alkalic character of the series.

Hawaii↗