Short-term and localized plume-slab interaction explains the genesis of Abukuma adakite in Northeastern Japan

The pulse-like adakite eruption in Mt. Abukuma, northeastern Japan at ~16 Ma has been considered peculiar because the subducting Pacific slab was too old to have been melted. Recent studies suggested that the injection of hot asthenospheric mantle as a temporal temperature anomaly into the corner of the mantle wedge was responsible for partial melting of the subducting slab, producing adakitic magma. However, the pulse-like and localized eruption of the Abukuma adakite poses a problem to the above model because rollback of the Pacific plate for ~10 Myr should have resulted in injection of the hot asthenospheric mantle into the corner of the mantle wedge along northeastern Japan, Sikhote-Alin, and Sakhalin. In addition, no quantitative examination of the interaction between the hot asthenospheric mantle and cold subducting Pacific plate has been performed. In this study, we used a series of two-dimensional kinematic-dynamic numerical subduction models to evaluate slab melting by the injection of a short-term temperature anomaly into the mantle wedge. Our model calculations show that injection of the short-term temperature anomaly into the corner of the mantle wedge resulted in slab melting at ~17 Ma, but that the duration of injection should be <5 Myr to comply with the pulse-like eruption of the Abukuma adakite at ~16 Ma. The localization of the Abukuma adakite, which excludes other areas of northeastern Japan, as well as Sikhote-Alin and Sakhalin, implies that the short-term temperature anomaly existed as a blob, which may have resulted from the penetration of the mantle plume through a neck in the subducting Pacific plate. The rising hot blob of the mantle plume from the slab neck was entrained to the corner flow of the mantle wedge and arrived at the slab surface at ~17 Ma. The pulse-like and localized Abukuma adakite was thus the consequence of short-term and localized plume-slab interaction in the Abukuma region.