It is possible to conclude that the andesite magmas are produced by fractional
crystallization of basalt magma based on mineral assemblages, major element variations
and strontium isotope ratios. However, REE and Ba concentrations and patterns are not
consistent with this hypothesis. Accordingly, it is more probable that andesite and basalt
magmas are formed independently by nearly the same degree of partial melting of hydrous
and less hydrous parts of upper mantle peridotite, with increasing temperature, at the
depths of 40 to 60 km.