11:00 〜 13:00
[SVC28-P01] Future adakitic volcanism in central Myanmar?
キーワード：Myanmar, adakite, magma genesis, magma differentiation, assimilation-fractional crystallization
Recently, three Quaternary volcanoes in central Myanmar (Popa, Monywa and Singu) are well studied by several researchers. Among the studies, we present a model for the petrogenesis of magma with adakitic affinity for Mt. Popa, the largest of three Quaternary volcanoes. The edifice is composed of Popa Plateau (0.8–0.6 Ma) with high-K rocks and a stratovolcano (<0.33 Ma) predominantly composed of medium-K rocks with adakitic affinity (Mg# 45–63, Sr/Y >40). The distinct K contents indicate that the adakitic magmas cannot be derived from Popa high-K rocks, but they share trace-element signatures and Sr-Nd isotope ratios with medium-K basalts from Monywa volcano. We have estimated that primary magma for medium-K basalts was generated by partial melting of wedge mantle with normal potential temperature (TP 1330–1340 °C) under wet conditions (H2O 0.25–0.54 wt %). Mafic adakitic magma (Mg#~63) was derived from the medium-K basaltic magma by fractional crystallization of a garnet-bearing assemblage at high pressure, and felsic adakitic rocks (Mg#~45) were produced by assimilation-fractional crystallization processes at mid-crustal depths. Melting in the wedge mantle source was probably induced by asthenospheric upwelling that is recognized in tomographic images. These results indicate that mantle melt production and differentiation in transcrustal magmatic systems is ongoing beneath Popa and may fuel future adakitic volcanism via the outlined model.