The Origin of the Paleo‐Kuril Arc, NE Japan: Sediment Provenance Change and its Implications for Plate Configuration in the NW Pacific Region since the Late Cretaceous

The Nemuro Belt is a tectonic belt in the Paleo-Kuril Arc system, the NW Pacific region. The Paleo-Kuril Arc has been interpreted as an intra-oceanic arc system between the Izanagi and Pacific plates during the Late Cretaceous, suggesting that the boundary between these plates was a trench. However, this study shows it was a volcanic arc that developed atop a continental margin. To determine the nature of this arc during the Late Cretaceous, U-Pb ages of detrital zircons from the Nemuro and Urahoro groups in the Paleo-Kuril Arc were analyzed. Our results identify two distinct types of detrital zircon U-Pb age distributions. The first (Type 1) is characterized by multimodal age distributions with peaks ranging from ca. 1.8 Ga to 78 Ma. The other (Type 2) exhibits a unimodal age distribution with a peak at 60–52 Ma. These different age distributions indicate a provenance transition occurred between the Late Cretaceous and Paleogene. Precambrian zircons in Type 1 sandstones indicate that the Paleo-Kuril Arc was part of a continental plate, presumably the Okhotsk Block, in NE Asia during the Late Cretaceous. In contrast, Type 2 sandstones were supplied only from the magmatic arc region that the Izanagi-Pacific Ridge subduction could have activated. This provenance transition suggests the initially continental arc became separated from its continental source at the beginning of the Paleogene