We present new data on the geologic position, composition, and isotope characteristics of the Early Cretaceous granitoids of the Samarka terrane, Sikhote-Alin’, formed on a transform continental margin. Geological and geochronological data show that these granitoids were generated at two stages of magmatism: in the first half (Hauterivian–Barremian, 130–123 Ma) and second half (Albian–Cenomanian, 110–98 Ma) of the Early Cretaceous. Granitoids of the first stage form an autonomous (free of basic precursors) unimodal melanogranite–granite association and are characterized by normal alkalinity with domination of K over Na, low contents of Ca, and elevated contents of Al2O3. By composition, these are S-granites with a model Nd age of ∼1.3 Ga. Granitoids of the second stage are of more diverse petrogeochemical types. They show wider variations in K/Na and A/CNK, are richer in Ca and, sometimes, Sr, and are poorer in P than the granitoids of the first stage. Their compositions form a continuous trend from S- to I-granites, and their model Nd age is ≤1.2 Ga. Comparison of the petrochemical, trace-element, and isotope characteristics of the Early Cretaceous granitoids and upper-crustal rocks (sandstones and siltstones of the turbidite matrix of a Jurassic accretionary prism and basalts from the inclusions in it) of the Samarka terrane and the coeval garrboids has shown that the potassic S-granitoids formed at the early (Hauterivian–Barremian) stage of magmatism as a result of the anatexis of upper-crustal sedimentary rocks. At the late (Albian–Early Cenomanian) stage, the intrusion of mantle magmas led to a temperature increase in the lower crust, which favored more active anatexis, involvement of high-melting substrates (oceanic basalts) in the granite formation, and interaction of mantle and crustal magmas. This resulted in a great diversity of granitoids (from S- to I-type).

The paper presents geological, geochemical, and isotopic data on metamorphic rocks in the Anuy block (dome) in the Northern Sikhote-Alin and the surrounding sedimentary rocks of the Samarka accretionary prism. The geochemistry and isotopic composition of the amphibolite-facies metamorphic rocks (variably migmatized gneisses and crystalline schists) in the Anuy block and unmetamorphosed Jurassic-Cretaceous sediments surrounding the block are proved to be similar. All of them corresponded to the erosion products of the transitional-type crust (mature island arcs and active continental margins), have similar major- and trace-element compositions, and Nd model ages of 1.25–1.4 Ga. The geochemistry and isotopic parameters of metapelites in the Anuy block are principally different from those of analogous rocks in the Khanka Massif (the latter rocks are erosion products of the mature crust and have a Nd model age of 1.7–1.9 Ga). The metabasites, which are found as beds and lenses in gneisses and crystalline schists in the Anuy block and among sedimentary rocks surrounding the block, have a composition corresponding to oceanic basalts of the N- and E-MORB types. Based on the synthesis of geological, geochemical and isotopic data it was suggested that the Anuy block could be not a fragment of the basement of an ancient continent (as was believed previously) but rather a complex of the Early Cretaceous granite-metamorphic core of the Cordilleran type.

The variations of petrogenic oxides and trace elements have been studied in the Cretaceous volcanic rocks recovered by a deep borehole from the depth interval of 1253–4011 m on Moneron Island. The volcanic section is subdivided into two complexes: the Early Cretaceous and Late Cretaceous. The rocks of the Early Cretaceous Complex occur below 1500 m. Chemically, they belong to low-potassium island arc tholeiites, and their trace element distribution suggests their formation in a suprasubduction mantle wedge under the influence of water fluids that were subsequently released from subducted sediments and oceanic plate during the dehydration of subducted sedimentary rocks and oceanic basalts and, finally, mainly from basalts. The Early Cretaceous basalts from the borehole are interpreted as ascribing to the frontal part of the Moneron-Samarga island arc system. The volcanic rocks of the Late Cretaceous Complex are situated at depths above 1500 m. They also were formed in a suprasubduction setting, but already within the East Sikhote-Alin continental-margin volcanic belt that was initiated after the accretion of the Moneron-Samarga island arc system to the Asian continent. The island-arc section of the Moneron borehole contains basaltic andesite dikes, which are geochemically comparable with the Early-Middle Miocene volcanic rocks of Southwestern Sakhalin.

The results of investigation of spatially separated Early Cretaceous island arc terrains, which are located in the central and northern Sikhote-Alin, Sakhalin and Moneron islands, and northwestern Japan, are given. A variant of Early Cretaceous paleotectonic reconstruction of the Asia-Pacific margin where all up-mentioned terrains combined into a single paleo-island arc system is proposed.

Basalts developed on the right bank of the Matai River belong to the Samarka terrane (Central Sikhote Alin), which is a fragment of the Jurassic accretionary prism. They associate with Carboniferous-Permian reef limestones, Permian pelagic cherts, Jurassic hemipelagic cherty-clayey deposits, and terrigenous rocks of the near-continental sedimentation area. The petrogeochemical features of the basalts provide insight into the character of the volcanism in different settings of the ancient Pantalassa ocean. In terms of chemistry, the Carboniferous-Permian basalts are similar to the within-plate ocean-island basalts related to plume mantle sources. They were presumably formed in an oceanic area with numerous islands and seamounts. The Permian basalts associated with cherts are tholeiitic in composition and were formed from depleted mantle in a spreading center located in the pelagic area. The Jurassic basalts are of plume origin and, in terms of geochemistry, occupy an intermediate position between OIB and E-MORB. They were presumably formed in a convergent zone in a geodynamic setting of rapid oblique subduction.

In the stratigraphic sequence of volcanic rocks in the Eastern Sikhote Alin, Maestrichtian-Danian predominantly andesitic volcanics are characterized by a boundary position between the Late Cretaceous subduction, mostly acid volcanic rocks and Cenozoic post-subduction basaltoids. Data on these rocks are important for elucidating the genesis of andesitic magmas, constraining and specifying the geodynamic evolutionary stages in this territory, and revealing the conditions under which the parental melts of these rocks were derived and evolved. Results of detailed mineralogical and geochemical studies, including ICP-MS analysis for trace elements point to a hybrid character of the andesitic volcanic rocks and an important role of fractional crystallization and crustal contamination in their genesis. Although geological evidence (variations in the style of volcanism, the composition of its products, and the character of their distribution) testifies to a change in the geodynamic environment in the Eastern Sikhote Alin in the Maestrichtian-Danian, geochemically the volcanics of this age range are typical subduction-related rocks with anomalously low concentrations of Nb and high contents of K, Ba, Rb, Pb, and U. The volcanic piles contain no adakites, which are indicators of the geodynamic environment in which slab windows are formed. The inconsistency between geological and geochemical indicators of the geodynamic environment suggests certain genetic features of the transitional magmatic series. The parental magmas of the andesitic volcanics were derived from the suprasubduction mantle wedge, which had been metasomatically recycled in the course of the dehydration and melting of the subducted oceanic slab. The increasing extension provided the possibility for the parental basaltic magmas to enter upper crustal levels, where they could interact with the host rocks and form hybrid andesitic melts.

The Middle Cenozoic evolution of magmatism in the Schmidt Peninsula between 37 and 25 Ma began with eruptions of subalkaline and moderately alkaline andesite, latite, trachyandesite, and trachyrhyolite lavas and ended with subvolcanic intrusions of highly alkaline strongly undersaturated essexites. According to trace-element data, magmatism evolved from melting of a mantle source in the zone of ocean-continent plate convergence to small-degree partial melting in lithospheric mantle at the final stage. This succession is generally typical of Late Cenozoic continental-margin magmatism in southeastern Russia. The similarity in the Middle and Late Cenozoic stages of magmatism is evidence for their individual significance.

The Early Cretaceous volcanic rocks of the Mariisky sequence and Early Cenozoic extrusive-vent rocks of Cape Mary are exposed at the northwestern extremity of Schmidt Peninsula, north Sakhalin. In chemical composition, all the rocks are subdivided into four groups. Three groups include the volcanic rocks of the Mariisky sequence, which consists, from bottom to top, of calc-alkaline rocks, transitional calc-alkaline-tholeiite rocks, and incompatible element-depleted tholeiites. These rocks show subduction geochemical signatures and are considered as a fragment of the Moneron-Samarga island arc system. Trace-element modeling indicates their derivation through successive melting of garnet-bearing mantle and garnet-free shallower mantle sources containing amphibole; pyroxene; and, possibly, spinel. The mixed subduction and within-plate characteristics of the extrusive vent rocks of Cape Mary attest to their formation in a transform continental margin setting.

Geological, petrochemical, and geochemical data are reported for volcanic rocks of a Cretaceous pull-apart basin in the Tan Lu strike-slip system, Asian continental margin. A comparison of these volcanic rocks with magmatic rocks from typical Cenozoic transform margins in western North America and rift zones of Korea made it possible to distinguish some indicator features of transform-margin volcanic rocks. Magmatic rocks from strike-slip extension zones bear island-arc, within-plate, and, occasionally, depleted MORB geochemical signatures. In addition to calc-alkaline rocks, there are bimodal volcanic series. The rocks are characterized by high K2O, MgO, and TiO2 contents. They show variable enrichment in LILE relative to HFSE, which is typical of island-arc magmas. At the same time, they are rich in compatible transition elements, which is a characteristic of within-plate magmas. The trace-element distribution patterns normalized to MORB or primitive mantle usually display a negative Ta-Nb anomaly typical of suprasubduction settings. Their Ta/Nb ratio is lower, whereas Ba/Nb, Ba/La, and La/Yb are higher than those of some MORB and OIB. In terms of trace-element systematics, for example, Ta-Th-Hf, Ba/La-(Ba/La)n, (La/Sm)n-La/Hf, and others, they fall within the area of mixing of magmas from several sources (island arc, within plate, and depleted reservoirs). The magmatic rocks of transform settings display a sigmoidal chondrite-normalized REE distribution pattern, with a negative slope of LREE, depletion in MREE, and an enriched or flat HREE pattern. The magmas with mixed geochemical characteristics presumably originated in a transform margin setting in local extension zones under the influence of mantle diapirs, which caused metasomatism and melting of the lithosphere at different levels, and mixing of melts from different sources in variable proportions.

Based on structure, mineralogy, petrography, and geodynamic setting of sedimentation, Barremian(?)-Albian terrigenous rocks in the Kema terrane (Eastern Sikhote Alin) are interpreted as back-arc rocks of the Moneron-Samarga island-arc system. The composition of terrigenous rocks indicates that an ensialic volcanic island arc, the basement of which was composed of the oceanward-advancing continental crust fragment, served as the main source of clastic material. Genetic features of rocks suggest their formation in the lower zone and near the foothill of submarine slope, as well as in adjacent areas of the basin plain. Accumulation of the thick gravitational sequence in the rear zone of the island arc was accompanied by active volcanic processes.

A geochemical study of the Cenomanian andesitic and basaltic volcanic rocks in the lower part of the Eastern Sikhote-Alin volcanic belt was performed. Petrologic and geochemical features of the rocks correspond to products of calc-alkaline magmas of the subduction-related continental-margin belts. The Cenomanian volcanics differ in some geochemical features from the Aptian-Albian Sikhote-Alin island-arc rocks and the Albian-Cenomanian rocks characterizing the geodynamic regime of a Californian-type transform continental margin.

Cobalt-platinum-rich ferromanganese crusts are typical of submarine ridges of the Western Pacific. Also, the hydrothermal auriferous sulfide ores are first revealed within central part of the East Pacific Rise. The authors have found a close correlation between both enriched contents of platinum-group elements in the crusts and enriched concentration of gold in the seafloor sulfide ores in host volcanic rocks from different structures of the Pacific. The data obtained enable us to consider the Pacific regions of metal (Pt, Au) enrichment as a result of leaching of these metals from volcanic rocks, affected by heated water in convective systems. The source of phosphorus in the phosphorites associated with ferromanganese crusts in the West Pacific is likely to be similar.