Origin of the early Cenozoic belt boundary thrust and Izanagi–Pacific ridge subduction in the western Pacific margin

Abstract

The belt boundary thrust within the Cretaceous-Neogene accretionary complex of the Shimanto Belt, southwestern Japan, extends for more than~1 000 km along the Japanese islands. A common understanding of the origin of the thrust is that it is an out of sequence thrust as a result of continuous accretion since the late Cretaceous and there is a kinematic reason for its maintaining a critically tapered wedge. The timing of the accretion gap and thrusting, however, coincides with the collision of the Paleocene-early Eocene Izanagi-Pacific spreading ridges with the trench along the western Pacific margin, which has been recently re-hypothesized as younger than the previous assumption with respect to the Kula-Pacific ridge subduction during the late Cretaceous. The ridge subduction hypothesis provides a consistent explanation for the cessation of magmatic activity along the continental margin and the presence of an unconformity in the forearc basin. This is not only the case in southwestern Japan, but also along the more northern Asian margin in Hokkaido, Sakhalin, and Sikhote-Alin. This Paleocene-early Eocene ridge subduction hypothesis is also consistent with recently acquired tomographic images beneath the Asian continent. The timing of the Izanagi-Pacific ridge subduction along the western Pacific margin allows for a revision of the classic hypothesis of a great reorganization of the Pacific Plate motion between~47 Ma and 42 Ma, illustrated by the bend in the Hawaii-Emperor chain, because of the change in subduction torque balance and the Oligocene-Miocene back arc spreading after the ridge subduction in the western Pacific margin.

Amalgamation of the Ryoke and Sanbagawa metamorphic belts at the subduction interface: New insights from the Kashio mylonite along the Median Tectonic Line, Nagano, Japan

“…9.2.1 | Rapid subsidence in the subduction zone Seton et al (2015) reported that plate-mantle reorganization resulting from the Izanagi-Pacific Ridge subduction occurred between 60 and 50 Ma. Similar tectonic records related to Izanagi-Pacific Ridge subduction between 60 and 50 Ma are also indicated from the magmatic hiatus at that time, as well as the age gap recorded in the accretionary complex and forearc basins along the proto-SW Japan arc (Kimura et al, 2019;Nakajima, 1994Nakajima, , 1997Wu & Wu, 2019). Thus, the two mylonitization episodes along the MTL took place just before the subduction of the Izanagi-Pacific Ridge.…”

Initiation and Evolution of the Shanxi Rift System in North China: Evidence From Low‐Temperature Thermochronology in a Plate Reconstruction Framework

“…In the back‐arc of the Japan arc, an incipient rift system of the Japan Sea formed in the middle Eocene and is characterized by marine transgression, magmatism, and a pulse of cooling recorded by fission track ages (Kano et al., 2007). In the meantime, a phase of exhumation took place during the early to middle Eocene within the Shimanto Belt, a long‐lived (Late‐Cretaceous to Miocene) accretionary complex in the forearc of Japan (DiTullio & Byrne, 1990; Kimura et al., 2019; Raimbourg et al., 2014). Furthermore, a global‐scale plate reorganization has been recognized within and around the Pacific realm at around 50 Ma (Seton et al., 2015; Whittaker et al., 2007).…”

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

“…Recently, the subducted remains of the Izanagi plate have been identified under the Eurasian plate by means of seismic tomography, indicating that the ridge that subducted beneath NE Asia at that time was not the Kula-Pacific Ridge but the IPR (Figure 14a; Seton et al, 2015;Whittaker et al, 2007;Wu & Wu, 2019). Kimura et al (2019) updated their model accordingly, but the supporting data provided were insufficient. Wu and Wu (2019) reported a near-synchronous disruption in magmatism between Japan and Sikhote-Alin at 56-46 Ma that is consistent with the subduction of the IPR at that time, which may have led to the reorganization of the Pacific plate at ca.…”

“…Ridge subduction is known to cause uplift in the forearc region (Cande et al, 1987;Cande & Leslie, 1986;Nelson & Forsythe, 1989;B. Taylor &Exon, 1987), andKimura et al (2019) suggested that subduction of the IPR caused the uplift of the Yezo forearc basin and Kamuikotan metamorphic zone around 50 Ma (Figure 15a). Thus, the elevated accretionary complexes most likely gravitationally collapsed to the trench floor, emplacing the large olistostromes around the same time as the in situ greenstones were emplaced.…”

“…Recently, a new interpretation of ridge subduction in NE Asia considers the possibility that the Izanagi-Pacific Ridge (IPR) approached NE Asia during the early Paleogene (Kimura et al, 2019;Miyazaki et al, 2015;Seton et al, 2015;Wu & Wu, 2019).…”