Collisional bending of the western Paleo‐Kuril Arc deduced from paleomagnetic analysis and U–Pb age determination

Abstract

The Paleo-Kuril Arc in the eastern Hokkaido region of Japan, the westernmost part of the Kuril Arc in the northwestern Pacific region, shows a tectonic bent structure. This has been interpreted, using paleomagnetic data, to be the result of block rotations in the Paleo-Kuril Arc. To understand the timing and origin of this tectonic bent structure in the Paleo-Kuril arc-trench system, paleomagnetic surveys and U-Pb radiometric dating were conducted in the Paleogene Urahoro Group, which is distributed in the Shiranuka-hill region, eastern Hokkaido. The U-Pb radiometric dating indicated that the Urahoro Group was deposited at approximately 39 Ma. Paleomagnetic analysis of the Urahoro Group suggested that the Shiranuka-hill region experienced a 28 clockwise rotation with respect to East Asia. The degree of clockwise rotation implied from the Urahoro Group is smaller than that of the underlying Lower Eocene Nemuro Group (62) but larger than that of the overlying Onbetsu Group (−9). It is thus suggested that the Shiranuka-hill region experienced a clockwise rotation of approximately 34 between the deposition of the Nemuro and Urahoro Groups (50-39 Ma), and a 38 clockwise rotation between the deposition of the Urahoro and Onbetsu Groups (39-34 Ma). The origin of the curved tectonic belt of the Paleo-Kuril Arc was previously explained by the opening of the Kuril Basin after 34 Ma. The age constraint for the rotational motion of the Shiranuka-hill region in this study contradicts this hypothesis. Consequently, it is suggested that the process of arc-arc collision induced the bent structure of the western Paleo-Kuril Arc.

Origin and evolution of the Paleo‐Kuril arc inferred from detrital zircon U–Pb chronology in eastern Hokkaido, NE Asia

“…Distribution of terranes belonging to the Paleo‐Kuril arc (modified from Katagiri et al, 2019) and paleomagnetic declinations of the terranes with 95% confidence limits (Fujiwara et al, 1995; Fujiwara & Kanamatsu, 1990; Hamano et al, 1986; Nifuku et al, 2009). The Yusenkyo formation was deposited during the late Campanian–early Maastrichtian (Kanamatsu et al, 1992) and the Nakanogawa group during the Paleocene–early Eocene (Nanayama et al, 2019).…”

“…The current strikes of the Tokoro Belt (Nikoro and Saroma Groups) and the Yubetsu Group between the Shiranuka and Kitami hills are NNE-SSW to NE-SW, as is the strike of the Nakanogawa Group on the eastern side of the Hidaka Mountains. Paleomagnetic data obtained from the Nemuro Group in the Shiranuka hills and from the Yusenkyo Formation show that the Tokoro and Nemuro Belts were bent clockwise by 90 or more from an initial east-west strike in the original stage of the Kuril arc-trench system (Hamano et al, 1986;Kimura, 1990;Fujiwara & Kanamatsu, 1990;Kanamatsu et al, 1992;Fujiwara et al, 1995;Katagiri et al, 2019; Figure 3). Correcting for this bending requires that the PKA associated with the Olyutorsky arc (OAT in Figure 1) also originally had an east-west to ENE-WSW strike (Hamano et al, 1986;Kimura, 1990;Kanamatsu et al, 1992;Katagiri et al, 2019;Kimura & Tamaki, 1985;Nanayama et al, 1993Nanayama et al, , 2021Vaes et al, 2019; Figure 3).…”

The emplacement ofin situgreenstones in the northern Hidaka belt: The tectonic relationship between subduction of the Izanagi–Pacific ridge and Hidaka magmatic activity

“…The Nemuro Group comprises Upper Cretaceous to middle Eocene forearc basin sediments of the paleo-Kuril arc (Figure 1; Kiminami, 1983;Okada et al, 1987). This group was covered by thick upper Eocene conglomerate of the Urahoro Group (zircon U-Pb age 39 Ma; Katagiri et al, 2019), which contain fan-delta and alluvial-fan facies (Figures 1 and 15b;Nanayama et al, 1994). The conglomerate includes red chert and greenstone clasts derived from the forearc Nikoro Group in the Tokoro belt (Nanayama et al, 1994).…”

“…Recently, Katagiri et al (2019) reported U-Pb ages and paleomagnetic measurements for the Nemuro, Urahoro, and Onbetsu groups in the Shiranuka Hills (Figure 1) that provide interesting context to the evolution of the NHB. They showed that the arc-arc collision between the paleo-Kuril and paleo-Japan arcs occurred at the end of the deposition of the Nemuro Group, at approximately 50 Ma.…”

“…Based on the evidence presented herein, the time gap between the deposition of the upper Urahoro Group and the base of the Onbetsu Group (39-34 Ma) was contemporaneous with magmatic activity in the upper Hidaka metamorphic zone. Based on the hypothesis proposed by Katagiri et al (2019), the collision between the paleo-Kuril arc and NE Asia had a collision became the heat source lready begun at the time that the upper part of the Nemuro Group was deposited (50 Ma), and certainly before the deposition of the Urahoro Group.…”