In the northeastern part of the Sino-Korean platform to the southeast of the Khanka Lake, ophiolitic rocks such as serpentinite, talc-magnesite rock, clinopyroxenite, gabbro, diabase and basalt were emplaced into the early Cambrian limestone in a WNW direction, and were unconformably covered by the middle Cambrian conglomerate. Heavy mineral fraction from the conglomerate is rich in chromian spinel grains, which chemically resemble those in the underlying ophiolitic ultramafic rocks. Most of the fresh chromian spinel grains in the ultramafic rocks and conglomerates are moderately chromian (Cr#=0.4-0.7), highly magnesian (Mg#=0.5-0.6) and poor in Ti and Fe3+ indicating common harzburgite protolith. However, some chromian spinel grains and their ferritchromit rims and veins are unusually rich in manganese (up to 19 wt.% MnO), indicating metasomatism before the conglomerate sedimentation. The basaltic rocks show MORB-like chemistry. These data suggests that the Khanka ophiolite formed at a rift zone in the Cambrian continental margin, prior to the development of the circum-Pacific accretionary complexes in Sikhote-Alin.

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This is a review paper presenting an original regional plate-tectonic model based on the data recently obtained on the geological structure and history of the Sea-of-Japan region. Several paleogeographic schemes for the Jurassic-Cretaceous time represent the author's geodynamic model for the development of this region. This model is clearly distinctive from the previous ones by postulating that the Californian-type transform margin has been one of the most significant geodynamic settings in the Mesozoic-Cenozoic East Asia. The author's paleogeodynamic model includes a geologic reconstruction of the pre-Neogene position of the Japanese Islands according to which the Central Sikhote-Alin, Tanakura and Median faults were parts of a single Early Cretaceous tectonic line. In addition, Early Cretaceous and Paleogene transform plate boundaries, Jurassic and Late Cretaceous supra-subduction continental margins, and Early Cretaceous island arc are recognized. The Early Cretaceous strike-slip movements likely resulted in a gigantic S-form structure of Sikhote Alin. Some Early Cretaceous and Paleogene magmatic rocks are recognized to indicate specific geodynamic structures, namely "slab windows".

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The authors examined and reviewed the sandstone composition of the late Middle Jurassic to the earliest Cretaceous in the Far East. Accretionary complex sandstones in Japan and in south Sikhote-Alin are divided into two units respectively. Brackish and shallow-marine sandstones in Japan mainly are divided into two floral regions. Using published data examined mostly by the traditional point-counting counting method, Q-F-R and Q-P-K diagrams of the traditional method were superposed on to Qm-F-Lt and Qm-P-K diagrams of the Gazzi-Dickinson point-counting method. As it turned out, tectonic provenance of sandstone assigned by geochemical data is consistent with that expected from its modal composition. Accretionary complex sandstone of this age in Japan is quartz-feldspathic sandstone as a whole. Sandstone of the Inner Zone is a little quartzose and sandstone of the Outer Zone is more feldspathic, although the difference of composition is not so distinctive. As for the brackish to shallow-marine sandstones in Japan, the sandstone from the South Kitakami and Abukuma belts (SKA) is quartzose, and that from the Tetori Group in the Hida and Hida Marginal belts (HHM) is feldspathic. The compositional features of the former are similar to those of the Inner Zone, and those of the later are similar to those of the Outer Zone. Tectonic provenance of the HHM is continental margin, but it might be more active than the source land of the other units.

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