Final magma storage depth modulation of explosivity andtrachyte-phonolite genesis at an intraplatevolcano: A case study from ulleung Island, South Korea

Abstract

Ulleung Island is the top of a 3000 m (from sea floor) intraplate alkalic volcanic edifice in the East Sea/Sea of Japan. The emergent 950 m consist of a basaltic lava and agglomerate succession (Stage 1, 1̇37-0̇97Ma), intruded and overlain by a sequence of trachytic lavas and domes, which erupted in two episodes (Stage 2, 0̇83-0̇77Ma; Stage 3, 0̇73-0̇24Ma). The youngest eruptions, post 20 ka BP, were explosive, generating thick tephra sequences of phonolitic composition (Stage 4), which also entrained phaneritic, porphyritic and cumulate accidental lithics. Major element chemistry of the evolved products shows a continuous spectrum of trachyte to phonolite compositions, but these have discor..