Origin and Evolution of the Paleo‐Kuril Arc Inferred from Detrital Zircon U–Pb Chronology in Eastern Hokkaido, NE Asia

The Nemuro and Saroma Groups and Yusenkyo Formation occur in eastern Hokkaido and are considered to be forearc or intra-arc basin sediments of the Paleo-Kuril arc (PKA) deposited during the Late Cretaceous to middle Eocene. To further clarify the origin of the PKA, we examined the U-Pb ages of detrital zircons within these sandstones and acidic tuff beds; based on our results, we drew the following conclusions. (1) The PKA originated from an oceanic island arc on the oceanic Izanagi Plate around 85 Ma, to which the Nikoro Group greenstone complex was accreted between 81-80 Ma; the Lowest Unit of the Saroma Group covered the surface of the Nikoro accretional greenstone complex. (2) The PKA then first collided with NE Asia around the beginning of the deposition of the Hamanaka Formation (similar to 70 Ma) and transitioned to a continental arc adjacent to NE Asia. This collision generated giant slump beds during deposition of the Akkeshi Formation. During deposition of the Kiritappu Formation, the entire Nemuro Peninsula was uplifted, supplying large volumes of clastic sediments. (3) Although we do not have data directly bearing on why the North American Plate was established in the edge of NE Asia, we speculate that it separated from the Eurasian continent around similar to 70 Ma when NE Asia first collided with the PKA. Subsequently, the PKA has behaved as part of the North American Plate. The Paleo-Japan arc (or East Sikhote-Alin arc) and the PKA became joined via the Hidaka Belt. Around 40 Ma, during the deposition of coarse conglomerate beds of the Urahoro Group, the PKA was uplifted and bent clockwise due to a second collision with NE Asia. (4) The modern Kuril arc was established around 36 Ma (late Eocene-early Oligocene), and the Kuril backarc basin opened into the present tectonic setting in the late Oligocene-early Miocene.