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The Sikhote-Alin Orogen in the southeast of Russia is a collage of geological terranes of various age and tectonic origin, which formed along the East Asian continental margin as a result of the Jurassic–Early Cretaceous subduction of the Pacific oceanic plates. The Jurassic Samarka accretionary complex (AC) and the Early Cretaceous Zhuravlevka turbidite basin in the southern part of the orogen are considered indicators of subduction continental margin and transform plate boundary regimes, respectively. The regime conversion was assumed at the end of the Jurassic, when subduction stopped. Our biostratigraphic study of radiolarians from siliceous and fine-clastic sedimentary rocks has revealed the latest oceanic deposits and the youngest, Early Cretaceous fragment of the Samarka AC in its less studied northeastern part, which is ascribed to the Anuy tectono-stratigraphic element. The well-preserved radiolarians allow accurate dating of cherts, siliceous mudstone, and mudstone. This and other available biostratigraphic data allow the reinterpretation of the stratigraphy of the accreted oceanic sedimentary rocks. The refined stratigraphy is interpreted as a subsequent change in depositional settings on an oceanic plate, which moves to the convergent plate margin. Cherts accumulated in an oceanic pelagic zone from the Middle Triassic to the Late Jurassic (Early Oxfordian). Siliceous mudstone were deposited in a hemipelagic zone in the early Oxfordian–middle Tithonian. Mudstone and siltstones deposited on an external slope of a deep trench in the late Tithonian–Berriasian. The sandy deposits were deposited in an axial part of the trench in the early Valangian, which best corresponds to the timing of accretion. Thus recognized early Valanginian accretion episode shows that subduction underneath the continental margin lasted longer than previously suggested. The onset of the transform continental boundary regime occurred later, probably, in the late Valanginian. This further details the Mesozoic evolutionary scenario, which was previously proposed for the Sikhote-Alin segment of the East Asian continental margin. We also refine the tectonic zonation and evolution of the Samarka AC. [ABSTRACT FROM AUTHOR]

Over the last decade, the Scythian Plate and the adjacent territory in the north have been covered by high-precision aeromagnetic (1 : 50000) and aerogravimetric (1 : 100000) surveys. An interpretation of the results allows us to reveal the Riphean-Early Paleozoic basement beneath the fold basement of the Scythian Plate. The ophiolitic complex, three volcanic-terrigenous sequences, basic intrusions and Early Paleozoic granitoids, as well as large folds have been identified within the basement. The large sheet of the Early Paleozoic basement thrust over the pre-Riphean basement of Baltica is traced along the entire Scythian Plate from the Azov Sea to the Caspian Sea. A presumably Early Kimmerian fold complex that underlies the Middle-Upper Jurassic platform cover has been recognized in the West Kuban Trough and Timashevsky Step. This complex is thrust in the northeastern direction over the Early Paleozoic fold complex. The above data make it possible to revise the geological history of the southern framework of the East European Platform and to prove the consecutive accretion of heterogeneous terranes differing in age from the south. [ABSTRACT FROM AUTHOR]

Abstract: The Upper Paleozoic orogenic belt of South Tian-Shan (STS) in Kyrgyzstan, Uzbekistan and Tajikistan consists of two structural domains: the south-vergent Bukantau–Kokshaal (BK) in the north and continuing into Xinjiang (China), and the north-vergent Zeravshan–Hissar (ZH) in the south, in Tajikistan. The Bukantau–Kokshaal fold belt was thrust south onto the Kyzylkum–Alai and Tarim continents in the Late Carboniferous. The BK belt is the most prominent collision-related, alpine-type part of the Paleozoic Tian-Shan and, as a prolongation of the Tian-Shan structure, shows close resemblance to the western (outer, west-vergent) part of the Urals. The Kazakhstan continent acts as a hinterland to the BK collision belt. Kazakhstan was constructed by accretion processes in which ancient (presumably Gondwanan) continental terranes and ocean-derived crustal elements of the Early Paleozoic to Early Carboniferous age played a role. The main episode of terrane amalgamation took place during the Middle and Late Ordovician. This appears to reflect active margin development in the Paleoasiatic Ocean, and resembles processes occurring in the recent Western Pacific. Geological differences in construction and protolith age of continental crust in the region are in general agreement with Pb– and Sm–Nd isotopic data. Relatively early (Visean) north-vergent thrust structures in Zeravshan–Hissar and eastern Alai (southwestern STS) bear some resemblance to the Central European Hercynides of Rheic origin, although this region became the location of active margin tectonic processes associated with the closure of the Paleotethys Ocean during the Carboniferous. Post-collisional magmatism occurred from ca. 300 to 270Ma and is represented by a variety of magma types from A-type granites to nepheline syenites. The spatial distribution of plutons appears to be controlled by transtensional structures associated with east–west, left-lateral wrench faulting. The presence of coeval alkali intrusions and plateau basalts in adjacent areas suggests that this magmatism may have been associated with a mantle plume. [Copyright &y& Elsevier]

Abstract: A Jurassic accretionary prism in the Sikhote-Alin-Amur area is an assembly of terranes, which are tectonic-sedimentary complexes consisting of multiple strongly deformed fragments of an oceanic plate. The stack of tectonic-stratigraphic units (complexes) in the prism section records its geodynamic history, each unit being signature of a geologic event on the Paleoasian eastern margin. The succession of accretion events brought together fragments of a Paleozoic oceanic plateau in the Early Jurassic and abyssal plain fragments of different ages in Middle and Late Jurassic time. [Copyright &y& Elsevier]