Neogene volcanism in Central-Eastern Hokkaido: Beginning and evolution of arc volcanism inferred from volcanological parameters and geochemistry.

Evolution of collision-related basins in the eastern end of the Kurile Basin, Okhotsk Sea, Northwestern Pacific

“…15 Ma), Goto et al (1995), Ikeda (1998) and Takeuchi et al (1999), however, dated and characterised the various volcanics in Hokkaido and Sakhalin, and suggested that the opening of the Kurile Basin continued until the Late Miocene (9-7 Ma). This conclusion was questioned by Hirose and Nakagawa (1999) who suggested that the geochemistry of 14-9 Ma andesite-dacite in Central and Eastern Hokkaido is characterised by arc types, and concluded that the opening of the basin ceased approximately 14 Ma. However, basalt, high Ti-content icelandite, and Fe/Mg andesite occurred in northeastern Hokkaido, suggesting the opening of the backarc from 7 to 14 Ma (Goto et al, 1995;Ikeda et al, 2000) The chemistry of the volcanics varied from arc-type to backarc type.…”

“…The volcanism is characterised by a negative Nb anomaly and shows arc characteristics. Hirose and Nakagawa (1999) interpreted this as the beginning of subduction-related volcanism induced by oblique subduction in the Kurile Trench. Ikeda et al (2000) performed geochemical analyses of basaltic rocks in the Monbetu area, and suggested that 12-10 Ma basaltic rocks show island-arc type features, whereas 9-7 Ma basalts can be classified as backarc basin basalts.…”

“…The shift in the tectonic regime might be related to the movement of the Kurile Arc and the opening of the Kurile Basin. Yahata and Nishido (1995), Yahata (1997), and Hirose and Nakagawa (1999) insisted that the Middle to Late Miocene unconformity is attributable to the uplift regime induced by oblique subduction in the Kurile Trench. In contrast, Goto et al (1995), Ikeda et al (2000), and Takeuchi et al (1999) suggested that the Kurile Basin might have still been active at that time.…”

“…A hypothesis regarding the shift in tectonic regime was also provided by Hirose and Nakagawa (1999) and Ikeda et al (2000). Hirose and Nakagawa (1999) carried out geological surveys and geochemical studies of volcanic rocks of Central and Eastern Hokkaido.…”

“…Hirose and Nakagawa (1999) carried out geological surveys and geochemical studies of volcanic rocks of Central and Eastern Hokkaido. They suggested that volcanism shifted from the north of Monbetu to the south, and volcanoes were arranged parallel to the arc in the Middle to Late Miocene.…”