Mantle diapir-induced arc volcanism: The Ueno Basalts, Nomugi-Toge and Hida volcanic suites, central Japan

Stratigraphic and geochronological data show that the late Cenozoic Ueno Basalts and related Nomugi-Toge and Hida volcanic suites of the Norikura Volcanic Chain, Japan, were active for ~ 1 million years. Temporal and spatial variations of the volcanic activity and chemistry of the volcanic products suggest that it was induced by a common mantle diapir. The Ueno Basalts are small monogenetic volcanoes scattered over an area 50 km in diameter, and comprise a small volcanic province. The Ueno Basalts are almost all subalkalic basalt to basaltic andesite, erupted through the late Pliocene to the earliest Pleistocene (2.7–1.5 Ma). Andesite to dacite of the Nomugi-Toge volcanic rocks were concurrently active in the back arc side, and two eruption stages (2.6–2.2 and 2.1–1.7 Ma) are recognizable. Two voluminous dacite and rhyolite ignimbrites, the Hida Volcanic Rocks, were erupted deeper in the back-arc region, at ca 1.75 and 1.7 Ma. Both the Nomugi-Toge and Hida suites are also subalkalic, except for the last ignimbrite. In the Ueno Basalts, alkali olivine basalt was erupted in the earliest stage, and was followed by subalkalic basalt, showing that the magma segregation depth ascended with time. This coincided with uplift of the volcanic province and with quasi-concentric expansion of the eruption centers, suggesting that an upwelling mantle diapir was the cause of the volcanism. The Nomugi-Toge andesite–dacite lavas and the Hida dacite and rhyolite ignimbrites are considered to have originated from the same mantle diapir, because of their close proximity to the Ueno Basalts and their near-contemporaneous activity. Mantle diapirs have a significant role in the origin of subalkalic volcanic rocks in the island arcs.