Comparative geochemical study of the cherty rocks of the Taukha terrane(Sikhote-Alin) and its paleogeodynamic significance

The article presents the results of a comparative geochemical study of cherts and siliceous–clayey rocks composing the tectono-sedimentary complexes of various structural levels of the Taukha terrain of the Sikhote-Alin Late Jurassic–Early Cretaceous accretionary prism. The data obtained show that the same-aged parts of the crosssections of the cherty–terrigenous sequences of the terrane lower and middle structural levels are characterized by significantly different contents and distribution patterns of major petrogenic oxides, trace, and rare-earth elements due to their accumulation in various facies of oceanic zones.The set of geochemical data indicates that the formation of both tectono-sedimentary complexes was carried out differently, gradually replacing each others' facies oceanic zones, and started in the near-spreading ridge area, then in the pelagial, and completed in the continental-margin deposition environment. Based on the time interval of the facies conditions changing for each complex(i.e., time of transition from one facies zone to another), the speeds of a paleo-oceanic plate motion(and, correspondingly, the speeds of spreading) for individual intervals of the Jurassic were calculated. Differences in the spreading speeds at various sites of a paleorift zone caused the turning of a paleocontinent margin contour and spreading ridge axis at the perpendicular position, which in turn caused change of the geodynamic mode on the eastern margin of the PaleoAsian continent at the Jurassic–Cretaceous transition.