Abstract

Abundant data from the Canary archipelago confirm an earlier suggestion based on scattered data from volcanic islands as a whole that, among published analyses of specimens from the oceanic basalt-trachyte association, trachytic materials are considerably more numerous than those of compositions intermediate between basalt and trachyte. Frequency distributions of SiO2, CaO, and Thornton-Tuttle index for the Canaries data are strikingly similar to those for the earlier worldwide collection. In the Canaries, as in most oceanic and many othere xamples of the basalt-trachyte association, trachyandesitic materials are probably considerably less abundant than trachytic materials. The relation is not readily explained by crystal fractionation but seems readily explicable by fractional melting

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