When the primary mantle melts, the crustal contamination of basaltic magmas distorts the source composition of the melting substrate and the degree of its trace element and isotopic enrichments. Such contamination is also important in understanding the interactions of contrasting structures of melts with mafic and felsic compositions or solid-phase systems (xenoliths) and the capacity of basaltic magmas in relation to the volumes of assimilation of incoherent highly polymerized crustal matter. First, the mechanism of diffusive interaction with crustal matter in nonsuperheated magmas is of interest when elements coherent to the melt or structural groups near the emerging cluster groups of the melt are extracted from xenoliths. Second, the selectivity of the contamination is of interest. The features of interactions between contrasting magmatic melts and melt-solid phase systems (melt -xenolith) are considered by analyzing the reaction products of such interactions, i.e., basalts contaminated with acid aluminosilicate matter and buchites (crustal xenoliths subjected to chemical modification and melting). For the largest late Miocene Shufan basalt plateau in southern Primorye (Russia), a process that involves the contamination of tholeiitic basalts with crustal aluminosilicate matter, which is unique in scale, has been recognized. As a result, large volumes of andesite-trachyandesite formed, which compose the upper horizons of the volcanic plateau. They are represented by massive "nonvesicular " lavas with banded texture caused by oriented layers of silicic potassium granophyre immiscible felsic selective melts from xenoliths. Two associated processes are clearly traced: mingling and mixing. Contaminated varieties with SiO2 contents of 57-60 wt% abnormal are enriched with xenocrysts of quartz and sieve-like melted plagioclase evenly distributed throughout the volume, which suggests an unusual mechanism of convective homogenization of xenogenic crustal sub-stances. Among the xenoliths, buchites are found to be chemically modified and remelted rocks of primary pelitic composition. They are represented by glassy varieties with different and unusual chemical compositions (SiO2 = 37-45 wt%, Al2O3 = 29-36 wt%, and FeO + Fe2O3 = 17-23 wt%) and are depleted in Mg, Ca, Na, and K. The mineral associations of buchites are represented by ultraferrous sekaninaites (f = 85-95%), hercynites (f up to 100%), whose compositions have no analogs in metamorphogenic rocks, sillimanite, mullite, tridymite, bytownite, baddeleyite, zirconium and high-aluminum armalcolite rich in pseudobrookite molecules, mon-o-lanthanum monazite, scandium-aluminum zircon and aluminosilicate-barium-phosphate matrix. The melting of pelitic xenoliths and diffusion interactions with basaltic magma formed iron-titanium rhyolitic liquids and anorthosite-like reaction coatings. The formation of buchites reflects a complementary relationship with contaminated basalt varieties due to the selective thermal and diffusive extraction of silicic-alkaline granitoid melts and a selective group of cations from pelitic xenoliths into the basaltic melt with the corresponding accumulation of refractory cations (Al, Fe, Ti, and Zr) in the restitic material. In the process of remelting xe-noliths, the phenomenon of destruction and dispersion of the crystalline substance of xenoliths into fractal fragments and clusters (up to micro -to nanosizes), which are grouped into immiscible liquid-like suspensions of quartz, feldspar, and hercynite-ilmenite composition, is identified.

The Cenozoic tephra deposits - products of explosive phreatic eruptions of maar volcanoes in the southwest of Primorye are studied. The deposits represent rhyolitic ash and pumice pyroclastic beds with a high terrigenous component, including tephroid pseudo-conglomerates. Isotopic dating of tephra beds established two time pulses of explosive volcanism: 30–34 Mya and 23–24 Mya. The first time pulse coincided with the beginning of the formation of marginal seas and continental coal basins. It corresponds to the most productive stage of coal accumulation, the burial of wood wastes and their coalification at a faster rate, and the development of a high-temperature geothermal field and can be compared with the well-known catastrophic eruption of Mount St. Helens in the U.S.A. The second time pulse of explosive volcanism had a regional character of manifestation. It is characterized by the formation of green tuff complexes on submarine elevations of the Sea of Japan as well as along the western and eastern coasts of Japan. Synchronously with the volcanic activity started the acceleration of the sinking rate of the Sea of Japan bottom in response to the active rising of asthenospheric diapirs. The established isotopic ages do not conform to the ages determined for fossil leaves and pollen from the deposits, which may reflect the climate-forming type of such an explosive process.

––New isotope-geochemical data on the volcanic complexes of the South Yakut and Martel volcanic depressions in southern Primorye are presented. Their formation in the early Eocene (54.3 Ma) and Late Cretaceous (83.5 Ma), respectively, is evidenced by U–Pb zircon dating (LA-ICP-MS). Based on the geochemical characteristics, it is concluded that the volcanics are typical A-type igneous rocks. Their formation coincides with the sudden change in the vector of motion of the Pacific slab with respect to the continent in the Campanian and Paleocene–Eocene, which caused destruction of the slab with its probable discontinuity and the injection of the subslab asthenosphere. The effect of mantle fluids on the continental lithospheric-rock melting determined the generation of magmas with the specific geochemical features of A-type igneous rocks. The regularities of their composition are due to the deep-seated reduced F-rich fluids that caused the intense differentiation of magmas accumulating fluidized melts enriched in mobile components in the apical part.

Research subject. This study was devoted to magmatic complexes in Northwestern Chukotka associated with the largest gold and silver deposits across Kupol’skii (Kupol field) and Ilirnei (Dvoinoe and September fields) ore junctions. Materials and methods. The petrogenic elements of ore-containing igneous rocks were determined using a spectrometer ICAP 6500Duo (USA). An elemental analysis of igneous and ore samples was performed by inductively coupled plasma spectrometry (ICP-MS). The age was determined by zircons (SHRIMP-II, VSEGEI isotope research center, St. Petersburg) using a laser ablation system NWR-213 (USA). Results. New information concerning the dating of magmatic complexes and gold-bearing magmatic systems in the ore junctions under study was obtained. It was established that the manifestations of magmatism in the Kupol and Ilirnei ore junctions differ in terms of the main phase formation age. The age of the Ilirnei ore junction, which is represented by large-volume intrusions of granitoids, leucogranites and volcanites of medium-basic composition, was determined to be 124–114 Ma. The age of mineralization, which is associated with later magmatism phases – small intrusions and a dike complex of predominantly granodiorite composition –, was estimated to be (93– 92) ± 2.0 Ma. In the Kupol ore junction, the magmatism associated with mineralization was dated 91.0 ± 1.4 Ma, while the age of rhyolite dikes containing mineralization was estimated to be 88.9–89.0 Ma.Conclusion. The results of the RMS analysis of the Kupol and Ilirney ore junctions suggest that ore formation in this region was connected with a single stage of activation of deep processes and mantle-crust interaction with participation of deep (mantle) fluids.

Обсуждаются вопросы масштабной контаминации базальтов Шуфанского вулканического плато (Приморье) селективными выплавками из ксенолитов. Селективно экстрагированные из ксенолитов кремне-щелочные жидкости лишь ограниченно смешиваются с базальтовым расплавом и образуют полосы гранофира, придающие лавам такситовую текстуру. Охарактеризованы уникальные составы бухитов - химически модифицированных при диффузионном взаимодействии с базальтовой магмой и селективно-расплавленных пелитовых ксенолитов. Их минеральные ассоциации представлены высокожелезитым кордиеритом (секанинаитом), ультражелезистым герцинитом, (Al, Zr) Fe-армолколитом, Zr-ильменитом, муллитом, силлиманитом, высоколантановым монацитом, бариево-фосфатной алюмосиликатной фазой. Особенности химического и минерального состава бухитов отражают накопление в реститовом веществе ксенолитов рефракторных элементов: Al, Fe, Ti, Zr, Ni, Cr с созданием ультраглинозёмистой, ультражелезистой, изначально несмесимой металло-силикатной композиции. Низкие свинцовые изотопные отношения в Шуфанских базальтах свидетельствуют о селективной контаминации веществом древнего кратонного основания. Наблюдается последовательный рост этих значений для базальтов, контаминированных верхнекоровым веществом, что отражает и изотопный состав бухитов.

The problems of large-scale contamination of the Shufan volcanic plateau (Primorye) basalts with selective melts from xenoliths are discussed. Silico-alkaline liquids that are selectively extracted from xenoliths mix only to a limited extent with the basalt melt, and form granophyre bands that give lavas a taxitic texture. The unique compositions of buchites (pelitic xenoliths chemically modified with a diffusion interaction with basaltic magma and selectively molten politic xenoliths) are characterized. The mineral associations of buchites are represented by highly ferriferous cordierite (sekaninaite), ultra-ferriferous hercynite, (Al, Zr) Fe-armalcolite, Zr-ilmenite, mullite, sillimanite, high-lanthanum monazite, and a barium–phosphate–aluminosilicate phase. The features of the chemical and mineral composition of buchites reflect the accumulation of refractory elements (Al, Fe, Ti, Zr, Ni, and Cr) in the restitic material of xenoliths, followed by the formation of ultra-aluminous, ultra-ferriferous, and initially immiscible metal-silicate composition. Low Pb isotopic ratios in the Shufan basalts indicate selective contamination with material of the ancient cratonic basement. A steady increase in these values is observed for basalts contaminated with the upper crustal material, which also reflects the isotopic composition of buchites.

The problem of the development of the ancient continental crust in the Primorye Region is discussed. It is substantiated by geological and isotope-geochemical criteria: a granite–metamorphic mineral composition of different-aged terrigenous deposits and pelagic cherts, occurrence of arkoses, as well as Proterozoic model age datings of sedimentary complexes and the occurrence of early Proterozoic zircons and monazites. The manifestation of potassium, high-Ba, LREE- and Nb-rich basite–ultrabasite magmatism, typical of Sino-Korean and Okhotsk Ba-bearing nuclears, of lengthy age intervals (Jurassic–Paleogene) in Primorye and the Amur Region is an important criterion.

Mass cobalt-rich ferromanganese microcrusts and nodules similar in morphology and chemical composition to cobalt-rich ferromanganese deep-ocean crusts were found in Cenozoic volcanic rocks in southern Primorye. Research has shown that ore genesis of this type is genetically related to argillization and destruction of siliceous rocks by CO2-rich fluids, which is confirmed by experimental data on carbon erosion of iron-containing materials. Two types of this fluid ore genesis are recognized: (1) relatively high-temperature (vapor-condensate), related to late volcanic processes and fracture gas infiltration, and (2) low-temperature (vapor-liquid-condensate), controlled by degassing followed by carbon mobilization (gasification). Primarily colloidal ferromanganese segregations have high contents of Co, Ni, Pb, Cu, and Ce, typical of oceanic ore genesis. Regardless of the concentrations of these metals in the protoliths, their contents in microcrusts are similar (n-10n wt.%). This indicates the same ore genesis mechanism and similar sorption properties of the colloidal ferromanganese material formed. Barium-and cerium-rich ferromanganese microcrusts and nodules are abundant. Condensed drops of iron-containing platinum were found in apobasaltic nickel-rich ferromanganese segregations. There is a cerium paradox expressed as a minimum or a total lack of cerium among rare-earth phosphates associated with ferromanganese microcrusts. Fluid destruction and oxide metallization of ocean-floor basalts are assumed to be the main source of metals for oceanic ferromanganese crusts and nodules. (C) 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

The processes of fluid destruction of various silicate rocks under diffusion of flows of compressed gases (mainly carbonaceous) were studied. The gas condensate nature was ascertained for the forming alumoslilicate and ore (cobalt–iron–manganese hydroxide) substances produced under this fluid destruction in the forms of microcrusts and microconcretions. The ore condensates contained in high concentrations the typomorphic elements of oceanic ferromanganese formations (Mn, Co, Ni, Cu, Pb, Ce, and Pt). The elemental composition of the ore oxide substance formed under the destruction of various silicate matrices exhibits a definite degree of endemism with prevalence of the Co–Mn association. The pronounced concentration of barium is related to the substantially carbonaceous composition of the fluid systems. A cerium paradox is revealed: Ce3+ is oxidized into Ce4+ and absorbed by ferromanganese hydrogel and the minimum of cerium appears in rare-earth phosphates.

U-Pb (SHRIMP-II) isotopic dating has been conducted for zircons of the ash sediments of the Ust’-Suifun Suite, which was the final stage of Late Cenozoic explosive volcanism in Southwest Primorskii krai. These pyroclastic units are widespread within sediments that fill in Cenozoic depressions including large coalfields. The concordant dates (23.7–24.6 Ma) are in line with the results of the K-Ar determinations for volcanic tephra (23.6–27.1 Ma) and correspond to the beginning of the active phase of spreading and taphrogenesis in the neighboring Trench of the Sea of Japan. These processes started as early as the Eocene and are reflected in the continental vicinity with the formation of riftogenic depressions and the occurrence of a peculiar gas volcanism.

Major oxides, trace elements (ICP-MS analysis), and Sr isotope ratios were analyzed in the late Miocene subalkaline and alkaline basaltoids of the southern part of the Russian Far East, which were formed during the final stage of the development of intraplate basaltic volcanism. Based on these data, variations in the main geochemical and mineralogical characteristics of various tectonomagmatic terranes were evaluated. The enriched and heterogeneous continental lithosphere modified to a varying extent by postaccretion subduction processes of different ages played a major role in the formation of the rocks. The first geochemical evidence was obtained for the subduction of the Solonker paleoceanic plate beneath the Amur microcontinent during the Permian.

Geological-petrological data were first obtained on the Early Miocene basaltoids and spinel-fassaite carbonatite tuffs of the Ambinsky volcanic structure in southwestern Primorye. The geological study of Ambinsky volcano allowed the reconstruction of stratigraphic sections across lava and pyroclastic basaltic rocks and stratified carbonatite tuffs. The chemical compositions of rocks and mineral phenocrysts from basalts and carbonatite tuffs are reported. The basaltoids are classed with undifferentiated moderately alkaline within-plate basalts. Evidence of carbonate-silicate immiscibility was found in the basaltoids and carbonatite tuffs. It was suggested that the formation of the carbonatite melt associated with simultaneous basification and abundant crystallization of spinel, fassaite, as well as oversaturation of the silicate system in Ca was caused by limestone assimilation, subsequent transformation of the melt, and liquid immiscibility. Thermal decomposition of carbonates with dissolution of released CaO in magma and accumulation of CO2 in a closed magmatic chamber gave rise to the autoclave gas effect and, correspondingly, heavy explosive eruptions atypical of such volcanic rocks. The genesis of carbonatite tuffs of Ambinsky volcano can serve as a model example of exsolution of carbonate melt in the moderately alkaline nonagpaitic basaltic system.