The structural features of rifting are reviewed during the formation of Cenozoic basins of the Western Pacific marginal seas. The examples of studied basins confirmed a hypothesis that rifting always starts from a passive phase and is only interrupted by episodes of active rifting. Rifting occurred under NE- and NNE-trending horizontal compression with the formation of either a chain of pull-apart basins or fields of diffuse rifting between the large strike-slip faults (the main part of the South China Sea). The NE and NNE directions of horizontal compression are probably related to the upper mantle convective flows from a spreading ridge of the Indian Ocean, which bear the plate fragments variously deformed during the transportation. The related NNE drift of the Indian, Australian, and Eurasian plates has no link with subduction processes from adjacent Paleopacific plates, which continue to move to northwest. The Western Pacific marginal basins mainly formed without any subduction influence from the Pacific Ocean and can be called backarc basins only based on geographical features.

This paper considers the results of the mineralogical and chemical study of sandstones and U–Pb isotope dating of detrital zircons from the Paleozoic–Early Mesozoic deposits of the Laoeling–Grodekovo terrane in western Primorye. It is shown that the sandstones of different age of the terrane differ markedly in their mineralogical and geochemical parameters and, hence, were derived from different sources. The sandstones of the Kordonka Formation are made up of fragments of basic and intermediate volcanic rocks of the oceanic island arc, as well as igneous and sedimentary rock associations of the oceanic island-arc basement. Eroded stable cratons and uplifted blocks representing crystalline basement inliers that are either flanked by rift zones or occurring along transform faults exerted a strong effect on the accumulation of sandstones of the Reshetnikovka, Barabash and Mangugai formations. The main suppliers of detritus were felsic igneous rocks with minor input from ancient sedimentary rocks. The rift margins and the eroded ensialic arc provided clastic material for the rocks of the Talmi Formation. The U–Pb geochronological studies of detrital zircons made it possible to constrain the age and possible position of igneous complexes that supplied clastic material to the sedimentary basins of the terrane. The sandstones were found to contain detrital zircons with concordant ages from 2553 to 205 Ma, which are dominated by Paleozoic zircons divided into several age groups. The zircons of Precambrian and Triassic ages are far fewer. In general, the revealed age ranges of detrital zircons from sandstones of the Laoeling–Grodekovo terrane agree fairly well with the known stages of granitoid magmatism in the eastern part of the Central Asian Orogenic Belt.

Basing on the structural and tectonophysic analysis of data collected from outcrops around Tonkin Gulf and the results of analysis of seismic setions of the Red river basin, the fourmain successivetectonic phases with specific paleostress fields since beginning of Cenozoic era have been established. The first middle Eocene-early Miocene (45-15.97 my) tectonic phase, with sub-latitudinal compression and sub-longitudinal extension, was accompanied by large scale sinistral displacement of the Red river fault, the extension centers of the Red river basin andseafloor spreading of East Vietnam Sea. The second middle-late of middle Miocene (13, 82-7, 25 my) tectonic phase, with sub-longitudinal compression and sub-latitudinal extension, has created a local depocenter N-S orientation; right-lateral strike slip of the Red river fault and first inversion of the basin. The third late Miocene (~7.25-5.33 my BP) tectonic phase, with NE-SWcompression, has caused strongest inversion in the Red river basin with strong uplift of some blocks and significant shrinkage of the RRB up to 15–20%. The fourth Quaternary-to-Recent tectonic phase, with NW-SE compression and NE-SW extension, is appeared in form of existing of the recent grabens of NW-SE direction, earthquakes and GPS data. Formation and development of the Red river basin was controlled by the tectonic activities and closely connected to NW-SE trending fault system of regional scale such as the Red river fault, Chay river fault, Lo river faults as well the local faults such as Ca river fault, Rao Nay river fault, Thakhek-Da Nang fault. Some spectacular examples for tectonic activity can be seen in form of geographic features of Vietnam, Laos and Thailand, in particular the mountain ranges, such as Truong Son (or Viet-Laos) belt. The Red river fault when comes to the sea becomes less active, while the other faults of the RRFS like Chay river and Lo river had played the main role in development of the Red river basin.

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.

The structure, composition, source areas of Lower Cretaceous terrigenous sediments and geodynamic conditions for their deposition in the Northern Sikhote-Alin are considered. The study established that in terms of mineralogical and geochemical parameters the sandstones, being either petrogenic or first cycle deposits formed by the products of the breakdown of bedrock from the source areas, correspond to graywackes. They are characterized by low maturity, weak lithodynamic reworking of parental rocks, and high rates of deposition. The paleogeodynamic interpretation of the data suggests sedimentation in the Early Cretaceous along the continent-ocean boundary in the basin related to large-scale strike-slip motions along the transform faults. The source area combined sialic land formed by granite-metamorphic and sedimentary rocks, a mature and deeply eroded continental-margin arc, as well as fragments of Jurassic-Early Cretaceous accretion prisms of the Sikhote-Alin with ophiolites incorporated into their structure. All this allows for the studied deposits to be considered as part of the Early Cretaceous Zhuravlevka pull-apart terrane.

The Kordonka Formation (lower Silurian) forms a lens-shaped tectonic block up to four km wide, extending southward from the Pogranichny village area (Primorsky Krai) for about 30 km. The formation is composed of argillaceous slate, volcanic-sedimentary rocks with horizons of sandstones, siltstones, conglomerates, and cherts, and also contains flows of basalts and andesite-basalts. The results of lithological-geochemical study of the terrigenous rocks of the formation indicate that the Kordonka Formation was accreted in the outer pre-oceanic part of the paleo-island arc system. The eastern part of the formation is intruded and partially assimilated granitoids of Middle Paleozoic and Late Permian age. The early phase of the granitoids was dated by U-Pb zircone 373.5±1.7 and 383.5±1.6 Ma (Late Devonian). The late phase is characterized by 261.2±1.2, 257.4±0.93 and 261.5±1.6 Ma (Wuchiapingian and Capitanian stages of the Middle and Late Permian). The Devonian granitods first identified in this area may be evidence of the Kordonka block accession to the Bureya-Jiamusi-Khanka orogenic belt consolidated during the Ordovician. The Kordonka terrane thus marks an independent Early-Middle Paleozoic episode in the formation and closure of the Central Asian paleo-ocean.

This paper studies the original results of the material composition analysis of the Early Silurian terrigenous deposits of the Kordonka formation of the Paleozoic – Early Mesozoic Laoeling-Grodekovo terrane of the South Primorye. The research is aimed at reconstructing paleogeodynamic setting of the deposition of sediments of the formation, and determining the type and mother rock composition of the feed sources based on the complex genetic interpretation of the material composition of rocks. It was established that mineralogically and geochemically formation of the rocks correspond to the typical graywackes and represent petrogenic or “first cycle” rocks formed mainly through the source rock failure. They are characterized by a low maturity, low lithodynamic recycling rate of mother rocks and their rapid burial. The interpretation of the results of the complex study of the material composition of the rocks was carried out on the basis of its comparison with the compositions of ancient rocks and modern sediments formed in the well-known geodynamic settings. The obtained data indicate that deposits of the Kordonka formation accumulated in a sedimentary basin connected with an oceanic island arc. Being built by basic and intermediate volcanic rocks as well as by igneous and sedimentary rocks that constituted its base, this island arc was the source area that supplied clastic material to the aforementioned sedimentary basin.

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.

We propose a scheme to subdivide the Samarka terrane, a Jurassic accretionary prism fragment, into tectonostratigraphic complexes. This subdivision provides a basis to study these formations and map them on a medium- to large-scale. Each complex corresponds to a certain stage in the accretionary prism formation. Thus, the complexes composed of subduction mélange and olistostromes (in our case, Ust-Zhuravlevka and Sebuchar complexes), can be correlated to episodes when the underthrusting of seamounts hampered subduction, as evidenced by seamount fragments contained in the complexes. Episodes of relatively quiet subduction have also been identified, resulting in complexes composed mainly of normally bedded terrigenous and biogenic formations (Tudovaka and Udeka and, partially, Ariadnoe complexes). Particularly considered is the Okrainka-Sergeevka allochthonous complex – a fragment of continental plate overhanging a subduction zone. It was included in the accretionary prism during gravitational sliding on the internal slope of the paleotrench. All volcanic rocks in the accretionary prism are allochthonous fragments of the accreted oceanic crust. The absence of the Jurassic-Berriasian volcanic belt related to this prism, as well as synchronous autochthonous volcanism, indicates that the Samarka terrane accretionary prism formed under conditions of flat-slab subduction, similar to modern examples along the Andean margin.

The paper presents data from geochemical and isotopic studies of the sandstones of the upper structural level of the Taukhinsky accretionary complex (Ustinovsky subterrane) of South Sikhote-Alin, exposed in two discrete areas of its distribution: southern and northern area. The studies showed a sharp difference in geochemical characteristics and, as a consequence, the sources of the turbidite clastic material of two areas. Sandstones of the northern range are characterized by high silicic acid, low levels of femic components and moderate alkalis. They are poorly depleted in comparison with PAAS incompatible elements and have Paleoproterozoic (approximate to 2 billion years) model Nd ages. According to the compositional features, the turbidites of the southern area correspond to lithogenic rocks - erosion products of recycled orogens with a noticeable admixture of acidic petrogenic material. Sandstones of the southern area have lower silica contents, are relatively enriched with femic components and calcium, have lower concentrations of incompatible elements, and young (0.94 billion years) model Nd ages. In terms of material characteristics, they correspond to petrogenic rocks - products of volcanic arcs erosion of medium acid composition. The difference in the sources of clastic material for the two areas is also indicated by distinct discrete trends in the evolution of the rare-element composition of rocks with a change in their siliceous content. From which it can be concluded that the differences in the material composition are due to the different compositions of the feeding provinces, and not to different fractions of the same spectrum of rocks in the source of clastic material. The synthesis of new data and the results of previous studies prove that the early stage of the formation of the Taukhinsky accretion complex was not accompanied by synchronous volcanic activity. Terrigenous rocks had local sources of clastic material, different for the rocks of the northern and southern areas.

Sciences, Vladivostok, e-mail: achashchin@mail.ru The results of mineralogical, geochemical, petrographic and other petrologic studies as well as assessment of PT parameters of crystallization of volcanic rocks of Late Triassic Talminsky complex are presented for the first time. The complex is mapped in the northern part of the Laoelin-Grodekovo terrane, within the Molokanka River basin, in the southwestern Primorye. Bedded deposits of the complex mainly consists of andesitic and dacitic rocks and their clastic lavas. Geochemical analyses of the moderately silicic volcanic have shown high concentrations of Sr, Rb, and Ba and low concentrations of Nb, Ta, and Ti which are characteristic features of suprasubduction rocks. This is also indicated by compositions of these rocks plotted on discrimination diagrams used for reconstruction of geodynamic settings of formation of basalts and andesites. However, geologic data available on the Laoelin-Grodekovo terrane structure, namely the absence of fragments of accretionary wedge as well as rocks of the Triassic oceanic crust, contradict the above assumption. The source of primary magmas for the Late Triassic volcanics of the complex was probably mantle substance that underwent metasomatic alteration during the Late Permian subduction. The PT conditions of formation of the Talminsky complex andesibasalts, andesites and dacites were determined based on chemical compositions of bulk rock and their clino- and orthopyroxenes. The studied high-alumina andesibasalts and moderately magnesium andesites crystallized at temperature 1076-1061 °C and 1099-1076 °C, respectively, whereas low-magnesium andesites and dacites had relatively lower temperature of crystallization: 1014-996

It is shown for the structures of the Late Permian–Early Triassic, Early–Late Cretaceous, and Early–Middle Miocene stages in the formation of the eastern margin of Asia that the evolution of the Earth’s crust included periods of tectonic reconstructions, which occurred practically instantaneously from the geological viewpoint. These periods are often shorter than the resolution of both local isotope and paleontological methods of dating.

—The East Sikhote-Alin volcanic belt extending for ~1500 km is commonly considered a single tectonomagmatic structure formed during the Late Cretaceous subduction and the Cenozoic oceanic-slab breakup and active asthenospheric diapirism under transform plate sliding. Based on analysis of the published geological information and the new data on the age and trace-element and isotope compositions of the igneous rocks of the Late Cretaceous Bol’ba Formation, it is shown that the initial stages of volcanism in the southern and northern Sikhote-Alin took place in different geodynamic settings. In contrast to the coeval suprasubductional volcanics of the southern sector (Primorye), the volcanic section of the Bol’ba Formation is dominated by magnesian (Mg# = 26–40) adakites (La/Yb = 19–34) and high-Nb basalts. This igneous rock association and the lead (Δ8/4Рb = 30–46) and neodymium (0.51279–0.51281) isotope ratios of the studied rocks suggest the influence of the “hot” oceanic asthenosphere on magma genesis. The earlier slab breakup north of 48–49 °N was due to the oblique convergence of oceanic and continental lithospheric plates in the Late Cretaceous, accompanied by sinistral shears. The results obtained indicate that the lateral zonation of the eastern Sikhote-Alin is due to different geodynamic settings of formation of its northern and southern sectors rather than variations in its basement composition. In theoretical aspect, the performed research is important for the correct reconstruction of the geologic events in zones of convergence of oceanic and continental plates. It is necessary to take into account not only the general direction of the convergence but also the configuration of the plate boundary.

ВВЕДЕНИЕИзучение особенностей магматизма, реализующихся в различных геодинамических режимах, является одной из важнейших задач современной геологической науки.Информация об источниках вещества, механизмах формирования и путях эволюции магматических расплавов позволяет более полно по

The article presents new geological, geochronological, mineralogical, geochemical, and isotopic data on the Early Cretaceous granitic rocks of the southern part of the Zhuravlevka Terrane (Sikhote-Alin). It is shown that four intrusive complexes containing significant amounts of granitic rocks were formed almost simultaneously in this area in the Early Cretaceous (about 100 Ma). These magmatic associations differ in rock set, their mineralogical characteristics, and chemical composition, varying from medium-potassium tonalites and granodiorites depleted in incompatible elements to shoshonitic monzonitic rocks enriched in HFSE and REE. The geochemical and isotopic characteristics of the granitic rocks indicate that the source of their melts was dominated by essentially juvenile metabasite crust with a limited contribution of the upper-crustal metasedimentary rocks. The diversity of geochemical types of the granitic rocks is explained by variable metabasite and metapelite contributions to their source, upper crustal contamination during magma ascent, as well as the variable contribution of the mantle source and different mechanisms of mantle–crust interaction.

The calculations which determine the chemical composition of the primitive magma are simple but they show changes in the temperature and pressure states of the magma source. The method is based on the addition of the chemical composition of the Olivine to the major element composition of the eruptive rocks which follows the formula: Ci = Ci-1+ 0.1 * Ci-1Ol. In accordance with the characteristics of the study area, we have made new additions to the calculation method. The calculation results are highly accurate when tested and compared with the chemical composition of the eruptive rocks. The chemical composition of the primitive magma solution is used to calculate the temperature and pressure states in the magma source. The results show that there is a difference in temperature and pressure in the source at different tectonic positions in the study area. Accordingly, the South Central coast region and the adjacent continental shelf are divided into two main types of eruptions. The first type of volcanic eruptions occurs at locations where major faults intersect and they are located north of the study area. The second type of volcanic eruptions in the form of a single volcano is located to the south of the study area and the southeastern continental shelf, and occurs in intracontinental extension structure.

The East Sikhote Alin volcanic belt (~1500 km long) is commonly regarded as a tectonomagmatic structure formed in the Late Cretaceous in a subduction environment, which was followed by the destruction of the oceanic slab and active asthenospheric diapirism in the Cenozoic. However, the nature of the lateral zonality of the Late Cretaceous volcanic complexes, which is distinctly expressed in a number of geological and metallogenic parameters, remains poorly studied. In this paper, this issue is considered on the example of the poorly studied Late Cretaceous Bolbinsk Formation of northern Sikhote Alin. Analysis of the published geological information in combination with geochronological, trace-element, and isotopic data indicates that the structure was developed in a non-subduction geodynamic setting. The predominance of magnesian (Mg# = 26–40) adakites (La/Yb = 19–34) and high-niobium basalts and low lead (Δ8/4Pb = 30–46) and high neodymium (143Nd/144Nd 0.51279–0.51281) isotopic ratios suggest an elevated permeability of the subducted slab and injection of a “hot” oceanic asthenosphere into the mantle wedge. Consequently, the lateral geological, geochemical, and metallogenic zonality of the East Sikhote Alin volcanogenic belt was formed at the early stages of its evolution as a result of the specific configuration of the Late Cretaceous continental margin.

The results of comprehensive (geological, geochemical, geochronological, and petro- and paleomagnetic) study of the Aptian–Albian rocks of the Kema Terrane and the northeastern Udyl segment of the Kiselevka–Manoma Terrane are presented. The obtained results suggest that the studied volcanogenic–terrigenous complexes of rocks formed in a suprasubduction zone at about the same time (early Albian, 110 Ma ago) at close latitudes but in different island arcs unequally distant from the continent: the complexes of the Kema Terrane at a latitude of 36° ± 6° N in the island arc close to the continent as evidenced by the petro–geochemical characteristics of the volcanites and the presence of ancient zircons in the sediments; and the rocks of the Udyl segment of the Kiselevka–Manoma Terrane at a latitude of 33° ± 5° N in an intraoceanic island arc separated from the volcanic arc of the Kema terrane by an interarc basin, which was wide and deep enough to avoid the influence of the continental source areas in the sediment accumulation zone of the Kiselevka–Manoma Terrane. Based on the conclusions, the geodynamic reconstruction is developed for the formation and history of motions of the studied rock complexes during the oceanic plate movement, their displacement along the transform margin, as well as post-accretionary movements at various distances to the current position with the following coordinates: Udyl 52° N, 140° E; Kema 45°–46° N, 136°–137° E.

This paper presents data on the geological position, geochemistry, age, and isotopic characteristics of the granitoids of the southern part of the Voznesenka terrane, Southern Primorye (Muraviev–Amursky Peninsula and its vicinities). All of the studied granitoids were formed in three stages: the Ordovician, Silurian, and Permian. The Silurian and Permian ages of the granitoid intrusions have been previously determined (Ostrovorussky Massif, 432–422 Ma, and 250 ± 4 Ma, early and late associations, respectively; Sedanka massif, 261 ± 3 Ma). The granites of the Artem and Nadezhdinsky massifs define an U–Pb zircon age of 481 ± 6 and 452 ± 4 Ma, respectively. The geochemical and isotope data show mainly the crustal nature of the granitoids. Their formation was related to melting of relatively immature rocks of the continental crust (mafic–intermediate volcanic rocks). The Nd isotope composition of the granitods (TNd(DM–2) = 1.3 Ga) indicates the absence of the mature ancient crust at the basement of the southern Voznesenka terrane. The maximum contribution of mantle sources to the granite formation is recorded in the Permian associations. A comparison of the peaks of intrusive magmatism in the southern part of the Voznesenka terrane and adjacent territories suggests that the formation of the granitoids of the Muraviev–Amursky Peninsula and its vicinities was caused by the interaction of continental blocks with two oceanic basins: the Paleoasian (and its fragments) and Paleopacific ones.