EarthRef.org Reference Database (ERR) -- Macdonald 1949

This paper provides a good review of petrologic and geologic literature for other islands, as well as for Hawaii, and represents the first modern classification of Hawaiian basalts by modal and normative mineralogy. Macdonald summarizes the geology and gives a simplified geologic map of each island and summarizes the geology of each of the five volcanoes on Hawaii. Ninole Hills are considered to be an older part of Mauna Loa, rather than a separate volcanic center. He tabulates average rock composition for each of the Hawaiian Islands and considers that olivine basalt is the parent for all Hawaiian magmas. He also tabulates the average chemical composition of different rock types. He considers that olivine in picrite basalts has accumulated by crystal settling, and also interprets dunite inclusions to have been derived by settling of olivine, but notes that the latter have undergone recrystallization and possible crushing prior to eruption. He discusses previous hypotheses, including Daly's conjecture that olivine crystallizes from superheated melts. Macdonald states that basalts differ from olivine basalts only in the absence of olivine phenocrysts. He makes normative calculations to demonstrate that Hawaiian andesites and trachytes can be derived from average Kilauea olivine basalt by simple crystal differentiation. He discusses in detail the origin of ankaramitic basalts which do not fit simple crystal accumulation from an olivine basalt parent, concluding that limestone assimilation is necessary. He discusses origin of the other late-stage basalts and the difficulties in deriving them from an olivine basalt parent and describes and rejects volatile transfer and remelting of wall rocks as necessary to the origin of Hawaiian lavas. He discusses limestone assimilation and concludes that, while not necessary for formation of the alkalic series, the conditions are possible for it to occur. The article ends with a comparison of Hawaiian lavas with those from other South Pacific islands.