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This paper reports new geochronological data on metagranitoids (U–Pb SIMS) and ophiolites (Sm–Nd) from the Khanka massif. New and published data define the Early Neoproterozoic Matveevka–Nakhimovka terrane with 935- and 915-Ma early suprasubduction magmatism, 850–880-Ma and 757-Ma withinplate and Pacific-type transform margin magmatism, as well as the Late Neoproterozoic–Early Cambrian Dvoryan and Tafuin terranes with 543, 520, 517, and 513-Ma suprasubduction magmatism. These two terranes are separated by a suture (Voznesenka and Spassk terranes) formed by Ediacaran–Cambrian shelf deposits and a Cambrian accretionary wedge with ophiolites older than 514 Ma. The greater part of the Khanka massif formed in the late Cambrian, with the Kordonka island-arc terrane accreted at the end of the Silurian. The Sergeevka terrane of the Ordovician island arc joined it through the Early Cretaceous strike-slip movements. Heterogeneous structures of the main part of the Khanka massif can be traced to the north based on the analogous stages of magmatism and metamorphism, where the Jiamusi massif (including the East Bureya terrane) is an Early Neoproterozoic block and the eastern Songnen massif (including the West Bureya terrane) is a Late Neoproterozoic–Cambrian block. These blocks are separated by the Spassk–Wuxingzhen–Melgin suture formed by their collision in the Late Cambrian. The Bureya–Songnen–Jiamusi–Khanka superterrane formed as a part of the Gondwana supercontinent approximately 500 Ma ago through orogeny and accretion of the Rodinia supercontinent fragments. [ABSTRACT FROM AUTHOR]

The paper presents a review of processes of subduction or tectonic erosion at Pacific-type convergent margins (PTCM) including definition of "tectonic erosion", its triggers, driving forces and consequences. We review examples of tectonic erosion at the Circum-Pacific PTCMs and at the fossil PTCMs of the Paleo-Asian Ocean (PAO) currently hosted by the Central-Asian Orogenic Belt (CAOB). Recent geological and stratigraphic studies have shown two types of PTCMs: accreting and eroding. Accreting PTCMs consist of older deposits of accretionary and frontal prisms and grow oceanward, i.e. the trench retreats. Eroding PTCMs are characterized by the destruction of the prism, approaching arc and trench and typically form during shallow-angle and fast subduction of an oceanic slab with oceanic floor relief highs. The mechanism of tectonic erosion includes destruction of oceanic slab, island arcs, accretionary prism, fore-arc and related prism. Tectonic erosion is a common phenomenon at many Circum-Pacific PTCMs, e.g., in South America, Tonga and Nankai troughs, Alaska. Accretion and subduction of oceanic rises contributes greatly to the processes of formation, transformation and destruction of continental crust at PTCM. The episodes of tectonic erosion can be also reconstructed for an ancient ocean, for example, for the PAO, which evolution and suturing formed the CAOB. Many CAOB foldbelts (Altai, Tienshan, eastern Kazakhstan, Transbaikalia, Mongolia) carry signs of disappearance of big volumes of continental crust (arcs). Studying processes responsible not only for the formation of continental crust, but also for the disappearance of big volumes of crustal material is important for correct evaluation of the nature of intra-continental orogenic belts, e.g., CAOB, and development of reliable tectonic models. [ABSTRACT FROM AUTHOR]

The Circum-Pacific Late Albian–Cenomanian orogenic belts (including the Sikhote-Alin–Western Sakhalin belt) were formed as a result of the deformation of mainly epioceanic terranes as fragments of Jurassic–Early Cretaceous accretionary wedges with ophiolites and other fragments of oceanic crust, turbidite basins, and island-arc systems. To the west of the Sikhote-Alin–Northern Sakhalin belt and orthogonally, the previously consolidation structures include the Bureya–Jiamusi–Khanka fragment of the orogenic belt of the Late Cambrian–Early Ordovician consolidation of the Late Proterozoic–Cambrian complexes. Within this belt, four isolated outcrops of the Heilongjiang complex are mapped. This complex combines metamorphic rocks of the epidote–amphibolite and glaucophane–schist facies and represents a fragment of a Jurassic accretionary wedge. It was assumed that these outcrops marked a suture; in particular, they represent the remains of the closed Mudanjiang paleoocean, separating the original Jiamusi terrane (and the Bureya–Jiamusi–Khanka belt) located to the west of Central Asia structures. This paper provides data that indicate that the Heilongjiang complex does not mark a suture, but is an underground near-horizontal continuation of the marginal continental accretionary wedge of the Nadanhada–Bikin terrane (flat subduction model) brought to the surface at the antiform bending site. The unity of the compared parts of the accretionary wedge is emphasized by the close matrix ages, the similarity of detritus zircon populations, and similar composition and age of allochthonous inclusions (limestone, chert, Late Paleozoic, and Early Mesozoic basalt). One important common feature is that Late Paleozoic and Early Mesozoic basalts from allochthonous inclusions occur as the N-MORB and OIB types in both cases, without any suprasubduction volcanism traces in the matrix. The Heilongjiang complex forms, according to this interpretation, a tectonic window among the more ancient structures of the Jiamusi terrane. There is no need to assume the existence of a Mudanjiang Ocean to explain the formation of the Heilongjiang complex. The structural features of this complex and its bedding conditions can be explained by the flat subduction processes of the Pacific slab in the Jurassic and its deformation in the Early Cretaceous. [ABSTRACT FROM AUTHOR]

The Kiselyovka-Manoma accretionary complex formed at the end of the Early Cretaceous during subduction of the Pacific oceanic plate underneath the Khingan-Okhotsk active continental margin along the east of Eurasia. It is composed of Jurassic-Early Cretaceous oceanic chert, siliceous mudstone, and limestone that include a significant amount of basic volcanic rocks. The known and newly obtained data on the petrogeochemistry of the Jurassic and Early Cretaceous basalt from various parts of the accretionary complex are systemized in the paper. Based on the comprehensive analysis of these data, the possible geodynamic settings of the basalt are considered. The petrogeochemical characteristics provide evidence for the formation of basalt in different parts of the oceanic floor within the spreading ridge, as well as on oceanic islands far from the ridge. The basalts of oceanic islands are mostly preserved in the accretionary complex. The compositional variations of the basalts may be controlled by the different thickness of the oceanic lithosphere on which they formed. This is explained by the varying distances of the lithosphere from the spreading zone. [ABSTRACT FROM AUTHOR]

New petrogeochemical data were used to determine the conditions of the formation and tectonic setting of volcanic rocks of the Lake Udyl' area. These rocks were compared with similar rocks in the region. The volcanic rocks of the Lake Udyl' area are subdivided into two genetic types: (1) within-plate oceanic volcanic rocks ascribed to the accretionary volcanogenic–siliceous complex (Tithonian–Valanginian–Hauterivian–Barremian) similar to accretionary complexes in other segments of the Kiselevka–Manoma Terrane, and (2) suprasubduction-zone volcanic rocks from the island-arc volcanogenic-terrigenous complex (Valanginian–Hauterivian–Aptian–Albian–Cenomanian). A synthesis of new geological and petrogeochemical data, as well as previous geochronological and paleomagnetic data indicates the co-occurrence of genetically diverse complexes in the Udyl' segment. [ABSTRACT FROM AUTHOR]

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]

The Itmurundy zone of the northern Balkhash area is a Pacific-type orogenic belt. It possesses a complex geological structure and hosts rocks of mantle, accretionary and post-orogenic associations. The volcanic and sedimentary rocks of the accretionary association belong to three suites: Itmurundy (O1-2), Kazyk (O2-3) and Tyuretai (O3-S1). The suites are separated by tectonic unconformities or faults of three orders: 1) large regional faults; 2) medium faults separating mantle and oceanic accreted rocks; 3) small faults separating packages consisting of oceanic sediments. The Itmurundy Fm. (O1-2) is the most lithologically variable consisting of oceanic basalt, pelagic chert, hemipelagic siliceous mudstone and siltstone, and trench greywacke sandstone. The packages, each consisting of chert-siliceous mudstone, are separated from each other by 2nd and 3rd order faults of probably thrust nature, i.e. they are parts of duplex structures. The presence of duplex structures and the high degree of deformation of Itmurundy Fm. rocks are typical of accretionary complexes. The associations of volcanic and sedimentary rocks under study represent a full section of oceanic plate stratigraphy (OPS): basalt (MORB, OIB)—chert (pelagic)—siliceous mudstone, siltstone and shale (hemipelagic)—trench sandstones (greywacke). The structural position and the lithology of Itmurundy rocks accord well with the model of formation of accretionary complexes at Pacific-type convergent margins, in particular, those in the western Pacific. [ABSTRACT FROM AUTHOR]

The Kiselyovka-Manoma accretionary complex, formed at the end of the Early Cretaceous, is a part of the Early Cretaceous Khingan-Okhotsk active continental margin. It is located at the front of the Amur accretionary complex and is composed of Jurassic-Lower Cretaceous oceanic volcanic-siliceous deposits. The structural study of this complex in the Lower Amur region hSas made it possible to clarify its overall structure and to subdivide the folds with different morphologies and orientations into five types. The analyzed folding sequence is compared to the folds of the Amur accretionary complex. The fold kinematics indicates various senses of motions that do not reveal systematic kinematic patterns of stacking of the accreted tectonic slices. [ABSTRACT FROM AUTHOR]

The results of study of the volcanic rocks of the Khabarovsk accretionary complex, a fragment of the Jurassic accretionary prism of the Sikhote Alin orogenic belt (the southern part of the Russian Far East), are presented. The volcanic rocks are associated with the Lower Permian limestones in the mélange blocks and Triassic layered cherts. The petrography, petrochemistry, and geochemistry of the rocks are characterized and their geodynamic formation conditions are deduced. The volcanic rocks include oceanic plume basalts of two types: (i) OIB-like intraplate basalts formed on the oceanic islands and guyots in the Permian and Triassic and (ii) T(transitional)-MORBs (the least enriched basalts of the E-MORB type) formed on the midoceanic ridge in the Permian. In addition to basalts, the mélange hosts suprasubduction dacitic tuff lavas. [ABSTRACT FROM AUTHOR]