Fukutoku-oka-no-ba Volcano: A new perspective on the Alkalic Volcano Province in the Izu±Bonin ± Mariana arc

Pumice samples from Fukutoku-oka-no-ba in the Izu±Bonin ± Mariana (IBM) arc were analysed for 40 trace elements and Sr, Nd, and Pb isotopic compositions. These samples are shoshonites (59.4±61.8 wt% SiO2), characterized by high contents of K2O (3.74±4.64 wt%), Ba (1274±1540 p.p.m.), Rb (91±105 p.p.m.), and light rare earth elements. The characteristics of alkali-element enrichment are similar to those of other parts of the Alkalic Volcano Province (AVP) in the northern Mariana and southernmost Volcano arcs. Sr (Sr/Sr ˆ 0.7036±0.7038) and Pb isotopic compositions (Pb/Pb ˆ 19.08±19.11, Pb/Pb ˆ 15.62±15.63, Pb/Pb ˆ 38.85±38.91) of Fukutoku-oka-no-ba pumice are relatively radiogenic, whereas Nd is unradiogenic (Nd/Nd ˆ 0.51283±0.51286). Fukutoku-oka-no-ba is isotopically distinct from Iwo Jima and is similar to the Hiyoshi Volcanic Complex, suggesting that Fukutoku-oka-noba might have a magma source similar to that of the Hiyoshi volcanic complex. Plots of Pb and Nd isotopes for AVP lavas trend toward the ®elds of ocean island basalt (OIB) source and pelagic sediments, which are possible sources of AVP enrichments.