The Southern Volcanic Complex II consists mainly of basalts with some trachybasalls and basaltic trachyandesltes. Its lower sequence is formed by middle alkaline rocks whilst in the upper one only m ild ly alk ali H y + O I -n o rm a tive rocks are found. The variations in com positio n are largely explained by similar crystal fractionation models for both the lower and the upper sequences. The variation among d iffe re nt basaltic types is due to d iffe re n t extractio n rates o f ab out 10-15%, o liv in e being th e domin ant phase, followed, in a lesser proportion, by dinopyroxene. The difference between the most differentiated basalts and trachybasalts or basaltic trachyandesiles could be explained by extraction of dominant clinopyroxene with plagioclase and Fe-Ti oxide