Recently, much attention has been paid to the
origin of andesiteso f the calc-alkalines eries,w hich
are widely distributed in time and space in island
arcs and continental margins. Several new hypotheses
have been proposed on the basis ofthe results of
experimental petrology and geochemistry (c/. Allen
et al., 1972; Kushiro et a.,1968; Green and Ringwood,
1968; Boettcher, 1973; Ringwood, 1974).
These include formation of andesite magma by (1)
partial melting of hydrous mantle peridotite, (2)
partial melting of subducted oceanic crust, (3) magma
mixing and (4) amphibole fractionation of basaltic
magma. However, it is very difficult to find
direct evidence to evaluate these proposals