Based on ; 348 K-Ar and 61 FT age data, volcanic stratigraphical and physical volcanological studies(volume, rate and mode of eruption, and edifice shape), and whole-rock geochemical data, we discuss temporal and spatial variation in volcanic activity after 19 Ma at central and eastern Hokkaido, southern end of the Kurile arc.The regional horizontal stress field in the area has changed from extension (19-14 Ma), extension∼neutral (14-1 Ma) to compression (1-0 Ma) and volcanic rocks with strong arc characteristics have been erupted since 14 Ma. Scale of volcanism of 19-14 Ma was much smaller in scale (several km
3/My) than that of 14-0 Ma (several hundreds km
3/My). The former produced bi-modal and non-arc type rocks with high TiO
2 and Nb contents, suggesting that it was not related to subduction, but to plume induced by spreading of a back-arc basin (possibly the Japan Basin). Although volcanic rocks during 14-9 Ma show strongly arc characteristics, it is difficult to explain tectonic setting because of the scarcity of geological and geochemical data from the Kuril basin, which might influence volcanism on the stage. Clearly subduction-related volcanism occurred at least up to 9 Ma. However a small amount of high-TiO
2 (high-Ti) and icelandite-like andesitedacite often occurred during 9-1 Ma, distinct from the youngest rocks (1-0 Ma), which are mostly low-TiO
2 and calcalkaline types. High-Ti and icelandite-like rocks may represent differentiated arc type under extension∼neutral stress field (arc-extension type).Subduction-related volcanism of 9-1 Ma was developing under oblique subduction of the Pacific Plate. The back-arc (volcanic arc) sector could be under less compression thereby producing arc-extension type rocks, because that compressional stress from Pacific plate is largely converted into strike-slip motion of the fore-arc sliver. The obliquity of the subduction of the Pacific plate has temporally decreased and is very weak at present, suggesting that subduction-related volcanism changed by compression since less than 1 Ma and producing mainly calcalkaline rocks.
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