Figure 2

Composition of the dacite lavas from the Rishiri Volcano, shown in (a) FeO*/MgO–SiO₂ diagram, (b) Sr/Y–Y diagrams, (c) primitive mantle-normalised diagram of trace element concentration, and (d) primitive mantle-normalised rare-earth element concentration. In (a), the discrimination line between the calc-alkaline and tholeiite series is taken from ref. ²⁶. In (b), the compositional fields of the High-SiO₂ adakite (HSA) and adakite are taken from ref. ¹⁵ and ref. ¹³, respectively. In (a–d), the data of refs. ^23,53 are also shown. In (c,d), the trace element concentrations of primitive mantle are from ref. ⁵⁴.