Figure 1

Classification of volcanic rocks from the Izu-Oshima volcano using discrimination diagrams. (a) K2O versus SiO2 (wt.%) variation diagram. Boundary lines dividing the high-, medium-, and low-K series are after Middlemost (1975), Peccerillo and Taylor (1976), and Gill (1981). (b) FeO*/MgO versus SiO2 (wt.%) variation diagram to discriminate tholeiite (TH) versus calc-alkaline (CA) trends (Miyashiro 1974).