Abstract
The origin of historic potassic basalts (from the 1719–1721 AD eruption) from the Wudalianchi volcanic field, northeast China, is investigated. The samples contain ~5 vol.% olivine microphenocrysts, and are characterized by K2O enrichment (>4 wt.%) and an EM1-like isotopic signature. By using thermodynamic calculations with the observed petrological features of the basalts, the eruption temperatures of the magmas are estimated to have been about 1250–1260°C. Because the estimated temperatures are significantly higher than the estimated maximum temperature of the lithospheric mantle beneath the Wudalianchi volcanic field, the magmas have plausibly been derived from the asthenospheric mantle. We suggest that both the potassic- and EM1-like natures of the basalts originated from the mantle transition zone which was metasomatized by K-rich sediment fluids at ~1.5 Ga ago through a stagnation of an ancient slab. We infer that the Wudalianchi magmatism was caused by an upwelling of a hydrous mantle plume from the mantle transition zone which has been remarkably hydrated through stagnation of the ancient subducted slab and the recent Pacific slab.
