Two Distinct Back-Arc Closure Phases of the East Sea: Stratigraphic Evidence From the SW Ulleung Basin Margin

Abstract

This study focuses on revisiting the tectostratigraphic framework of the Ulleung Basin and conceptualizing neotectonics around the western East Sea margin. Based on the analysis of 2D and 3D multi-channel seismic reflection data and offshore drill wells, we divided the entire sedimentary successions of the Ulleung Basin into four tectostratigraphic sequences, named TS1 (c. 23–16 Ma), TS2 (c. 16–9 Ma), TS3 (c. 9–4 Ma), and TS4 (c. 4 Ma–present), in ascending order. The results show that each sequence has been deformed once or multiple times in different periods by juxtaposing two major compressional structures named the Dolgorae Thrust-Fold Belt and the Gorae Anticline. Interpretation of the stratal deformation and termination patterns of the syn- and post-deformational sequences of each structures suggests that the thrusting and folding of the Dolgorae Thrust-Fold Belt was active from c. 16 Ma to c. 9 Ma under the NNW–SSE compressional stress regime (Stage-2), whereas the Gorae Anticline was active from 4 Ma to the present under the ENE–WSW compressional stress regime (Stage-4). Between these two compressional events, there was an intervening period of regional slow subsidence driven by thermal contraction of the back-arc lithosphere and isostatic sedimentary loading (Stage-3). Based on the stratigraphic and structural reconstruction, we propose a 4-stage tectonic model: Stage-1) back-arc opening stage associated with the southward drift of the Japanese islands (c. 23–16 Ma), Stage-2) tectonic-inversion stage in association with the reorganization of the Pacific and Philippine Sea plates and clockwise rotation of SW Japan (c. 16–9 Ma), Stage-3) post-inversion stage with regional thermal and isostatic subsidence (c. 9–4 Ma), and Stage-4) neotectonic stage in which embryonic subduction is nucleating on the East Sea margins under the E–W compressional stress regime (c. 4 Ma–present).

Failing Subduction Initiation in an Opposing Pair of Incipient‐Diffuse Subduction Margins: A Case From the East Sea (Japan Sea)

“…In contrast to the eastern margin, broadly accepted as a plate boundary undergoing SI, the western margin has been regarded as a stable intraplate setting that has been tectonically dormant. However, an increasing amount of evidence points toward that the western East Sea margin as well is in the compressional neotectonic regime (Choi et al., 2008; Kim, Moon, et al., 2016; Kim, Rhie, et al., 2016; Kim, Yoon, et al., 2018; Kim, Ree, et al., 2018; Lee et al., 2022). Recent seismic reflection investigation has demonstrated that the western PDZ of the East Sea was reactivated into an incipient subduction zone under a regional E–W compressional stress regime since the Early Pliocene (Kim, Yoon, et al., 2018).…”

“…The tectonic inversion lasted for approximately 7 myr until the early Late Miocene (Lee et al., 2022), which formed a series of the Dolgorae‐San'in Thrust‐Fold Belt (Yamamoto, 1993) and the Tsushima‐Goto islands (Fabbri et al., 1996; Kim et al., 2008). Following tectonic inversion, the entire East Sea region experienced slow subsidence by thermal contraction of the back‐arc lithosphere and loading of thickly accumulated sedimentary succession (Ingle, 1992; Jolivet & Tamaki, 1992; Kim et al., 2013; Lee et al., 2022). At present, the East Sea sits within an E–W compressional regime since the Early Pliocene (c. 4 Ma) (Taira, 2001).…”

“…Following the tectonic inversion, the Ulleung Basin experienced tectonic dormancy, with a slow (∼100 m/myr) thermal subsidence until the Late Miocene (Lee et al., 2022). Currently, the basin is situated within an E–W compressional neotectonic stress regime, which is suspected to have induced incipient subduction along the western margin of the basin that was previously a dextral PDZ (Kim, Yoon, et al., 2018; Lee et al., 2022).…”

“…As the young Philippine Sea Plate replaced the old Pacific Plate, the tectonic stress regime on the southwestern margin of the East Sea changed from extension to compression (Lee et al., 2011; Yoon et al., 2014). The tectonic inversion lasted for approximately 7 myr until the early Late Miocene (Lee et al., 2022), which formed a series of the Dolgorae‐San'in Thrust‐Fold Belt (Yamamoto, 1993) and the Tsushima‐Goto islands (Fabbri et al., 1996; Kim et al., 2008). Following tectonic inversion, the entire East Sea region experienced slow subsidence by thermal contraction of the back‐arc lithosphere and loading of thickly accumulated sedimentary succession (Ingle, 1992; Jolivet & Tamaki, 1992; Kim et al., 2013; Lee et al., 2022).…”

“…In contrast to the active eastern margin, the western margin of the East Sea has been regarded as tectonically dormant (Lallemand & Jolivet, 1986; Yoon & Chough, 1995; Yoon et al., 2003). However, new geological/geophysical evidence suggests that this margin has also experienced incipient subduction (Kim, Yoon, et al., 2018; Lallemand & Arcay, 2021; Lee et al., 2022).…”