Late Jurassic to early Early Cretaceous tectonic nature on the NE Asian continental margin: Constraints from Mesozoic accretionary complexes

It is widely accepted that subduction of the Paleo-Pacific Plate beneath. Eurasia began in the early Mesozoic. However, the tectonic nature and processes of the NE Asian continental margin in the Late Jurassic to early Early Cretaceous remain unclear. In this contribution, lithological, provenance, and metamorphic-deformation data are used to constrain the formation of Mesozoic accretionary complexes (AC) along the NE Asian continental margin and determine the tectonic relationship between the NE Asian continental margin and the Paleo-Pacific Plate in the Late Jurassic to early Early Cretaceous. The Mesozoic AC formed during the Late Jurassic (including the Raohe AC in NE China; the Khabarovsk, Samarka, and Taukha ACs in the Russian Far East; and the Mino-Tamba AC in Japan) and Early Cretaceous (including the Shimanto AC in Japan and the Kiselevka-Manoma AC in the Russian Far East). The Jurassic AC underwent a complex evolution, including the formation of seamounts, Middle-Late Jurassic terrigenous clastic sedimentation adjacent to the trench; collision of seamounts with Eurasia, northward migration of the AC, early Early Cretaceous terrigenous clastic sedimentation, a second period of accretion, and final emplacement. The earliest Mesozoic AC arrived at the trench at ca. 195 Ma. Combined with the occurrence of early Mesozoic calc-alkaline igneous rocks along the NE Asian continental margin, we suggest that subduction of the Paleo-Pacific Plate beneath Eurasia began in the Early Jurassic. Jurassic AC in Japan was affected by a regional high-P/T metamorphic event at 160 Ma, which might have been related to subduction-collision of seamounts with Eurasia at the trench. Ages and Hf isotopic compositions of detrital zircon grains from the Middle-Upper Jurassic and Cretaceous AC sandstones, together with paleontological and paleomagnetic data, indicate that Jurassic clastic sediments were sourced mainly from the South China Block (SCB), whereas the Lower Cretaceous sandstones were sourced from the eastern Central Asian Orogenic Belt (CAOB). The inferred northward migration of Jurassic AC in the Late Jurassic to early Early Cretaceous indicates that the boundary between the NE Asian continental margin and the Paleo-Pacific Plate was characterized by strike-slip tectonics at this time, likely due to a small angle of obliquity in the subduction of the Paleo-Pacific Plate beneath Eurasia. In the late Early Cretaceous, westward subduction of the Paleo-Pacific Plate beneath Eurasia resulted in the emplacement of the Raohe and Khabarovsk ACs at 137-130 Ma and the formation of ACs in the Russian Far East and Japan.