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Russian Journal of Pacific Geology
Journal Prestige (SJR): 0.374

Citation Impact (citeScore): 1
Number of Followers: 0

Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1819-7159 - ISSN (Online) 1819-7140
Published by Springer-Verlag

[2469 journals]

The Bolshoi Payalpan Volcano (Sredinny Range, Kamchatka): Problematic
Aspects of the Convergence of Island-Arc and Within-Plate Petrological and
Geochemical Signatures in the Magmatic System
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  Abstract: Abstract New age, mineralogical, geochemical, and isotope–geochemical data on the rocks of Bolshoi Payalpan Volcano (Sredinny Range, Kamchatka) are presented and compared with the available data on the Nosichan and Belogolovsky volcanoes within the common Belogolovsky volcanic center. Basalts of the neck and upper lava complex of Bolshoi Payalpan Volcano resemble withinplate-type trachybasalts of Belogolovsky Volcano, and basaltic andesites of the lower lava and the cone complex are similar to the island-arc rocks of Nosichan Volcano. Analysis of the data we obtained indicates that spatiotemporal association of intraplate and island-arc volcanism at Bolshoi Payalpan Volcano is not accidental, but may be caused by a change in the degree of melting and depth of a common deep source with the involvement of a mantle diapir. The Belogolovsky volcanic center formed in the Late Miocene–Early Pliocene rifting setting. Its evolution up to extinction proceeded in the same geodynamic setting with increasing depth coupled with a decreasing degree of melting of a mantle source. Rocks of Early–Middle Pliocene Nosichan Volcano retain island-arc signatures under incipient rifting conditions, since they are related to the mantle reservoir that is located at a shallower depth and experienced a higher degree of melting. There is good reason for consideration of large volcanic centers as self-developing geological systems. As the endogenous activity attenuates, the degree of melting decreases and the depth of melting increases, thus leading to a change from island-arc to withinplate volcanism. The volcanic center becomes extinct.
  PubDate: 2022-04-01
Columbite–Tantalite of the Kester Deposit (Eastern Yakutia)
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  Abstract: Three mineral types of the columbite group have been revealed at the Kester Deposit (Eastern Yakutia), that is, columbite-(Fe), columbite-(Mn) and tantalite-(Mn), which are part of rare-metal granites, ongonites, albitites, and greisens. Columbite-(Mn) prevails: Ta/(Ta + Nb) = 0.30, and Mn/(Mn + Fe) = 0.64. The generalized formula of columbite–tantalite of the deposit is (Mn0.61Fe0.34)0.95(Nb1.37Ta0.58Ti0.04W0.03Sn0.01)2.03O6. Columbite–tantalite forms polymineral individuals with concentric growth zonality (from the core to the rim): columbite-(Fe) → columbite-(Mn) → tantalite-(Mn) + uranmicrolite → columbite-(Mn). In columbite of the Kester Deposit, WO3 is a typomorphic impurity, which is 2.67%, on average (formula coefficent, apfu is 0.04); the maximum value is 7.12% (apfu is 0.11). The isomorphic replacement of cations in the B position is assumed according to the following scheme: 2(Nb, Ta)5+ ↔ W6+ + Ti4+. In tantalite, SnO2 is a typomorphic impurity, which is 1.01%, on average (apfu is 0.03); the maximum value is 3.74% (apfu is 0.21). The paragenesis of the columbite group minerals includes albite, topaz, lepidolite, Nb-Ta-bearing cassiterite, wolframoixiolite, wolframite, U-Hf-bearing zircon, and struverite. At the Kester Deposit, the evolution of columbite–tantalite is accompanied by an increase in Ta/Nb, Mn/Fe, and Sn/W ratios manifested in the change of columbite by tantalite both in the process of the formation of ore-bearing rocks and in the rock series: rare-metal granites → albitites → greisens. The variation limits of Ta/(Ta + Nb) and Mn/(Mn + Fe) ratios are 0.07–0.74 and 0.16–0.96, respectively. The diversity and evolution of the columbite group minerals of the Kester Deposit indicate their belonging to the rare-metal ore-magmatic system, which includes ore-bearing rare-metal granites, albitites, and greisens. The presence of small intrusions of rare-metal granites and ongonites in the deposit area allows the forecasting of new objects with bedrock and placer columbite–tantalite mineralization.
  PubDate: 2022-04-01
The Influence of the Structure and Composition of Lithotectonic Units on
the Geochemical Specialization of Hydrothermal Mineralization of the
Kolyma Terrane, Northeast Russia
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  Abstract: Abstract This study focused on the relationship between the mineralogical composition of hydrothermal mineralization and the structure and lithology of host units with specific reference to the Kolyma passive continental-margin terrane (Northeast Asia). The long geological history of the terrane was shown to be reflected in the geochemical specialization and distribution patterns of gold–rare metal and porphyry copper mineralization. The Proterozoic host units of the Kolyma region influenced the geochemistry and isotope composition of the ores. The imbricate–thrust structure of the terrane was formed in the Precambrian and underwent several episodes of reworking in the Phanerozoic, thus contributing to the repeated rejuvenation of the ores.
  PubDate: 2022-04-01
The Deep Structure Model for Southern Kamchatka Based on 3D Density
Modeling and Geological and Geophysical Data
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  Abstract: Comprehensive deep geophysical studies were conducted along the profile lines in the south of Kamchatka. The aim of the research was to study the lithosphere in the zone of present-day volcanism and active seismicity. Geological and geophysical models of the crust and upper mantle were constructed along the profiles. The results were obtained as part of two-dimensional modeling of the geophysical fields. However, the data analysis shows that the territory is characterized by a complex geological structure, which is shown by the three-dimensional distribution of gravitating masses. This article presents the results of volumetric density modeling carried out for the area of southern Kamchatka, including the Sea of Okhotsk and the Pacific water areas, for the first time. The model is based on the technique of three-dimensional imaging of 2D-modeling results obtained from the network of intersecting profiles. The 3D modeling has revealed the isodensity surfaces that border layers of high density (≥3.33 g/cm3). Thus, the surface revealed beneath the oceanic water area is interpreted as a fragment of the top of the subducting plate and the surface under the peninsula is identified as the top of the paleosubduction slab. A subhorizontal high-gradient zone (3.0–3.3 g/cm3) is recognized on the density sections that intersect the 3D model, which is identified as the Moho boundary. A model of the subduction interaction between the oceanic and continental lithospheric plates is proposed. A two-dimensional model shows the formation of a transitional layer between the Moho boundary of the overhanging lithospheric plate and the top of the paleosubducting oceanic plate. A low-density zone is distinguished in the transitional layer, where separate maximally low-density areas are identified as melting chambers. The conditions are shown for the formation of the crustal block, with abundant basic–ultrabasic intrusions and the diorite–granodiorite intrusive massif. All ore occurrences and a gold deposit of the Karymshinsky Ore Cluster are located within the contours of the projection onto the surface of the deep high-gradient zone that borders a low-density zone. Ore occurrences are genetically related to the zones of crustal weakness where the epithermal deposits are formed in closed hydrothermal systems. By analogy, it is possible to forecast gold ore occurrences in other areas of the projection of the high-gradient zone.
  PubDate: 2022-04-01
Rare-Earth Element Mineralization in Argillized Granites of Southern
Primorye: New Data
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  Abstract: Abstract Rare-earth element (REE) mineralization in weathered granites of Primorye is localized in the basement rocks and rocks surrounding coal-bearing basins, which have been recently deformed and undergone argillic metasomatism. It was shown that the clay material from the zones of intense argillization can be a source of deficient REE and yttrium. The ion-sorbed and carbonate REE+Y species in them in combination with the clay composition of most of the ores make it possible to use inexpensive and low-toxicity salt and hydrochloric acid solutions during heap leaching.
  PubDate: 2022-04-01
The Records of Environmental Changes in Lacustrine–Swamp Sequences
within the Mountain Area of Iturup Island since the Late Glacial Period
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  Abstract: We have received unique material on the development of the natural environment for the last 12 400 cal. yr. BP in the central part of Iturup Island. High-resolution paleoreconstructions have been based on the multi-proxy study of paleolake sediments found on the plateau (height 400–420 m) located northwest of the Baransky Volcano. For the first time, a record of paleogeographic events has been obtained for the Late Glacial and the Early Holocene. The age model is based on nine radiocarbon dates. Diatom analysis has made it possible to distinguish 11 stages of lake–swamp evolution. The paleolake reached its maximum depth at ~9890–7900 cal. yr. BP and became extinct at 1400 cal. yr. BP. The vegetation development stages and the landscape change factors have been restored. The Younger Dryas cooling recorded in Iturup was characterized by humidity changes. The role of forest vegetation rapidly increased at the Pleistocene–Holocene boundary of ~11 470 cal. yr. BP under warmer climatic conditions. Distribution of dwarf pine as an indicator of stable snow cover has been analyzed. Dark-coniferous forests existed in the mountainous part of the island since the Late Glacial and were the most widespread in the Early Holocene. The onset of birch forest expansion at 6200 cal. yr. BP was related to the intensification of volcanic activity and frequent ash falls. A number of identified cold events were enhanced by the weakening of the warm Soya Current. The intensive transfer of allochthonous pollen from the southern Kuril Islands and the Japanese Islands at 3540 cal. yr. BP is a sign of cyclogenesis intensification in the Kuril Islands. The Holocene climatic rhythms in the landscape development of the Iturup mountains, as well as the influence of warm and cold currents and other regional factors, have been analyzed.
  PubDate: 2022-04-01
Correlation of the Acoustic Parameters and the Age of the Basal Horizons
of the Cenozoic Sedimentary Cover, the Sea of Japan
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  Abstract: The velocity sections and acoustic parameters of the sedimentary cover in the Central (Japan), Yamato (Honshu), and Tsushima basins, and the Kita–Yamato Trough of the Sea of Japan, as well as the rocks of the basement and the Cenozoic cover of the submarine Yamato Rise were studied. A comparative analysis of similar parameters of the Cenozoic basins in the South China and East China marginal seas was performed. The relationship between the acoustic properties (P-wave velocity, Vp) of the basal horizons and the age of the Cenozoic cover in the above basins was analyzed. The values of Vp = 3.0–3.6 km/s have been validated as the acoustic parameter of Paleocene–Eocene sedimentary strata. According to the studies we performed, the basal layers in the supposed depocenters of the Japan basins (Central, Yamato, and Tsushima) have Vp = 3.0–3.3 km/s, which indicates the Paleocene–Eocene age of the onset of their formation.
  PubDate: 2022-04-01
The Age of Gold Mineralization of the Elga Deposit, Mongol–Okhotsk Fold
Belt: 40Ar/39Ar Geochronological Constraints
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  Abstract: As a result 40Ar/39Ar geochronological studies, the age of gold mineralization has been determined for the Elga deposit that is located in the eastern part of the Mongol–Okhotsk fold belt. The age of ore metasomatites and ore-hosting hydrothermally altered carbonaceous sericite–feldspar–quartz schists is estimated at 139–137 Ma. The formation of ore mineralization of the Elga deposit is not likely related to magmatic processes, because the age of igneous complexes within the studied region is either younger or significantly older than the mineralization. An almost identical age of 139 Ma is identified for sericite from schists of the Talyma Formation beyond the ore zone. This indicates that the final stage of metamorphism and regional deformations, on one hand, and the formation of ore metasomatites, on the other hand, has similar age. In our opinion, the key role in mobilization and redistribution of ore matter and the formation of the Elga deposit belongs to postcollisional dislocation processes, which were accompanied by hydrothermal alteration.
  PubDate: 2022-04-01
Rare-Metal Granites of the Tigriny Massif (Sikhote-Alin): Geochemistry,
Mineralogy and Evolution
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  Abstract: Abstract This article describes the geological setting, geochemical features of rocks and the composition of the main minerals (micas, feldspars) of the granitoids of the Tigriny intrusion (Central Sikhote-Alin), associated with Sn-W mineralization. It is shown that the granitoids have high contents of fluorine and typomorphic trace elements and geochemically correspond to Li–F rare-metal granitoids. The evolution of rare-metal-granite magmas of the Tigriny massif was controlled by two main processes: fluid–magmatic interaction, which led to the formation of ultrapotassic pegmatoid granites, stockscheiders, and crystallization differentiation along the albite “trend,” which led to the formation of lower-silica aluminous sodic melts of the final phase. The latter were likely emplaced in an open or partially open-system conditions and experienced intense degassing during crystallization, which resulted in the formation of late plagioclase granites with lower contents of fluorine and typomorphic trace elements as compared to the earlier rocks. Separation of high-F fluids enriched in trace alkalis and ore components led to the formation of the large Tigrenok greisen body, which hosts the main volume of the richest ores of the Tigriny deposit.
  PubDate: 2022-02-01
The Structural Heterogeneities of the Geological Medium in the Сentral
Part of the Peter the Great Bay, Sea of Japan (from Detailed Geomagnetic
Studies)
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  Abstract: The results of detailed geomagnetic investigations of Peter the Great Bay significantly change the customary ideas about structural heterogeneities of geological environment. A new understanding of a morphology, stratification depth and material composition of anomaly-forming bodies have been obtained based on the classification of magnetic anomalies and petromagnetic characteristics of rocks. The issues of structural and tectonic zoning of the central part of the bay have been justifably resolved. For the first time in history the right wing scarp of the Muravyevsky horst-anticlinorium has been located, the amplitude of the displacement and the width of the horst have been determined.
  PubDate: 2022-02-01
Sources of Sediment Clasts and Depositional Environment of Sedimentary
Rocks of the Daur Series of the Argun Continental Massif
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  Abstract: Abstract This paper presents the results of geochemical and isotope-geochemical (Sm–Nd) studies of the Upper Riphean (') (in the Stratigraphic Scale of Russia) sedimentary rocks of the Urulungui and Dyrbylkei formations of the Daur Series in the Argun continental massif, as well as U–Th–Pb and Lu–Hf isotope studies of detrital zircons from these formations. Rocks of the Urulungui and Dyrbylkei formations differ significantly in their mineral composition and major-element composition, which is probably related to the degree of chemical weathering of source rocks. Analysis of the trace-element concentrations in the sedimentary rocks of the Urulungui and Dyrbylkei formations enabled us to establish that they were formed in a subduction-related setting. The presence of conglobreccias, conglomerates, gravelstones, fragments of igneous and volcanic rocks, the low level of roundness of clastic material, as well as the abundant Neoproterozoic detrital zircons in the formations, are evidence for tectonic and igneous activities in the region during sedimentation. Sedimentary rocks of the Urulungui and Dyrbylkei formations have two-stage Nd model ages of TNd(DM2) = 2.0–2.1 Ga and 1.6–1.8 Ga, respectively. The abundant Neoproterozoic zircons in sandstones of the Urulungui and Dyrbylkei formations suggest that Neoproterozoic igneous rocks that were widely developed within the western Argun continental massif were the main source of clastic materials. At the same time, the presence of Early Precambrian detrital zircons indicates that Early Precambrian rocks were also present in the source area. However, reliably dated Early Precambrian igneous and metamorphic rock associations have not yet been found within the Argun continental massif. Thus, it is possible that the rocks of the Daur Series form an “exotic block” involved in the Argun massif.
  PubDate: 2022-02-01
Giant Skarn Borosilicate Deposits: Derivatives of Fluid-Hydrothermal
Reworking of Atoll Fragments in Subduction Melange of Asian Mesozoic
Orogenic Belts
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  Abstract: Geological observations coupled with geochemical, isotope, and thermobarogeochemical research on danburite ores of unique skarn borosilicate deposits in their reserves in the Sikhote-Alin (Dalnegorsk) and in the Pamir (Ak-Arkhar) indicate lagoon strata and evaporites in the form of atoll fragments within the Mesozoic subduction mélange as the most probable boron source, which preceded the skarn formation. At the Dalnegorsk deposit, the fact that boron is mobilized by skarn-forming solutions from evaporite accumulations is directly confirmed by the heavier isotope composition of boron (δ11B = +17.7 ‰), which corresponds to marine evaporites, and a typical Li-rich fluid.
  PubDate: 2022-02-01
The Characteristics of the Geophysical Fields of the Pavlik Gold Ore
Deposit (Yana–Kolyma Metallogenic Belt)
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  Abstract: This paper reports the results of analysis of the geophysical fields of a gold deposit and reveals some of their typical features. The range of geophysical studies and data processing techniques for solving the problems of gold mineralization forecast within the Yana–Kolyma Metallogenic Belt is described. Based on the interpretation of the geophysical dataset, the geological and geophysical indicators of gold mineralization are proposed in the following hierarchical sequence: ore cluster–ore field–mineralized zone–ore body. One of the main interpretation techniques for determining the prospecting indicators of potential ore bodies (or high-grade intervals) is the study of induced polarization frequency responses.
  PubDate: 2021-12-01
  DOI: 10.1134/S1819714022010067
Rare-Earth, Noble, and Rare Metals in the Ores of the Algama Zirconium
Occurrence, Khabarovsk Krai
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  Abstract: Abstract Samples of ore and gravity concentrate from the Algama zirconium occurrence were studied. Concentrations of rare-earth elements (REE), and rare and noble metals were determined. The REE content is 200–300 g/t in the ore and reaches 400 g/t in the gravity concentrate. REE distribution patterns show a clear negative Ce anomaly and MREE and Y predominance. The ore and the concentrate have elevated Hf, W, U, Ta, Au, and Pt contents. Their source is the ancient weathering crust developed after ultra-alkaline rocks of the Ingili massif. The presence of a buried weathering crust enriched in valuable components is inferred in the studied area.
  PubDate: 2021-12-01
  DOI: 10.1134/S1819714022010031
The Geochemical Patterns of Native Gold from the Yugler Ore–Placer
Field (Northeast Russia)
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  Abstract: The results of a spectral study of 242 native gold samples from ore materials of indigenous deposits and relics of placer deposits in the Yugler ore-placer field were analyzed using the Leader and PROFILE software. The mineralization in black shale of the Yugler ore-placer field is characterized by the lead and copper geochemical specialization of native gold. This assigns it to the style of gold mineralization at the Degdekan deposit, but distinguishes it from most similar deposits in Russia and worldwide. Native gold in ore bodies and placers displays a distinct geochemical specialization. Native gold from ore bodies is high in As, Bi, and Pb; gold from the Yugler Brook placer, in Cu, Pb, Fe, and Mn; and placers of the Spokoinyi and Matrosov brooks, in Sb and Ag. In general, the vertical zoning of mineralization includes low-grade antimonious segregations of native gold in eroded parts of the sequence and high-grade bismuth–lead–arsenious grains, in its preserved parts. The general mineral–geochemical model of the formation of the Yugler ore-placer field is a space–time exchange of copper–polymetallic mineral assemblages with arsenic–bismuth–polymetallic and then with silver–antimony–polymetallic assemblages. The antimonious mineral assemblages were the most abundant in the southwest of the ore field.
  PubDate: 2021-12-01
  DOI: 10.1134/S1819714022010080
Bismuth Mineralization of the Belogorskoe Magnetite Deposit (Sikhote-Alin)
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  Abstract: The orebodies of the Belogorskoe deposit contain various bismuth minerals. Many of them are rare in nature or are rare mineral varieties. Among them are native bismuth, bismuthine, cosalite, gladite ('), jonassonite, a galenobismuthite variety enriched in Ag and Cu, bismite, bismutite, preisingerite, bismoclite, zavaritskite, and a large group of unnamed compounds. One specific feature of the endogenous bismuth mineralization of the deposit is its localization in the low- to medium- temperature hydrothermal alteration products of the early assemblages, especially in large carbonate (with fluorite) pockets in blocks of essentially magnetite ores, where it is closely associated with Au–Ag–Pd–Pt and Mo–W mineralization. A significant amount of Ag in the form of Ag–Bi minerals is also related with the bismuth mineralization of the Belogorskoe deposit. The close geochemical relationship of Bi, Au, and PGE in the processes of mineral formation at the Belogorskoe deposit is also manifested by the presence of the common minerals of these elements, such as jonassonite and the unnamed compound Ru(Pb,Ag)2Bi4. The association of bismuth and molybdenum–tungsten mineralization is a characteristic feature of the ores of some tungsten and molybdenum skarn deposits containing scheelite, molybdenite, and bismuthine as the main minerals. The presence of bismuth and noble-metal mineralization is most characteristic of gold and complex gold-bearing ores of hydrothermal deposits of various types. However, such metals as W, Mo, and Bi, as well as Au, Ag, Pd, and Pt, have no independent industrial role at the Belogorskoe deposit, unlike the deposits of the above-mentioned types, and are accompanying useful components relative to iron ores. Rocks and ores that compose the orebodies of the Belogorskoe deposit are Triassic metalliferous sediments that accumulated in island lagoons as a result of erosion of the lateritic weathering crust of ancient gabbroids, which were metamorphosed and partially regenerated during the Late Cretaceous. This accounts for the enrichment of ores in various metals, including Fe and Mn, and the presence of gold–silver–palladium–platinum, nickel–cobalt, and bismuth mineralization, which (including Bi compounds with Au and PGE) is characteristic of some ultramafic massifs.
  PubDate: 2021-12-01
  DOI: 10.1134/S1819714022010043
Authigenic Minerals of Paleozoic–Cenozoic Volcanogenic-Sedimentary Rocks
in the Southern Primorye Region
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  Abstract: Authigenic minerals of volcanogenic–sedimentary and sedimentary rocks have been studied from the Permian to the Miocene in the southern Primorye region. Corrensite, rectorite, highly ordered mixed-layer chlorite–smectite (corrensite-like) and illite–smectite (rectorite-like) varieties, mica, vermiculite-like varieties ('), chlorite, defective chlorite, kaolinite, calcite, and zeolites were found. Such a range of minerals indicates that the thickness of the deposites in the sedimentary basins studied could attain 3 to 5 km and the temperature of their formation was higher than 150°C. The formation of Lower Cretaceous and Paleocene sedimentary strata are characterized by similar features and probably first occurred in the shallow sea basin on the continental margin (rift stage), sometimes under conditions close to evaporitic (presence of corrensite'), with frequent alternations of the facial situation from shallow to deep sedimentation, episodic volcanic material supply and gradual deepening of sedimentation basins. It is proposed that in the Early Cretaceous and Paleogene, sedimentation basins that formed a scattered network on the continental margin of northeastern Asia evolved under an integrated mineralogical and tectono-sedimentological regime of crustal extension. The minerals were accumulated in the sediments, which were transformed during epigenesis in the following directions: (a) smectite–rectorite–mica; (b) smectite (palygorskite, sepiolite')–corrensite–chlorite. In the examined sedimentary complexes, three mineralogical “stages” have been distinguished: (1) chlorite-mica (mica-chlorite)–mica–chlorite (Permian-to-Cretaceous); (2) transitional–mixed-layer corrensite-like and rectorite-like minerals (Cretaceous–Paleocene–Eocene), and (3) smectite (from Oligocene up to the present).
  PubDate: 2021-11-01
  DOI: 10.1134/S1819714021060075
The First Data on the U–Pb Ages and Compositions of Zircons from
Ore-Bearing Syenites of Gora Rudnaya (South Yakutia)
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  Abstract: Abstract This paper presents the first isotope-geochemical study (SHRIMP-II, SIMS) of zircons from syenites of Gora Rudnaya (South Yakutia), which host the recently discovered Morozkinsky gold deposit. Gora Rudnaya is a laccolith located in the Central Aldan ore district. Vein and vein-disseminated gold mineralization occur in low-temperature acid metasomatites, beresites (Qz–Ser–Ank–Py), restricted to steeply dipping submeridional brecciation zones. According to zircon dating, the age of the ore-bearing syenite is approximately 130 Ma. The obtained age corresponds to the main magmatic stage and associated hydrothermal–metasomatic activity within the Central Aldan ore district. Two groups of zircons have been distinguished in syenites. The first group shows features of magmatic genesis. The second group reveals evidence of fluid reworking, in particular, elevated contents of U, Th, and some nonformula elements (LREE, Ca, Ti, and Sr). The presence of two zircon varieties that differ in composition and appearance but have the same age indicates that the magmatic crystallization of syenites from Gora Rudnaya and their fluid reworking occurred practically simultaneously.
  PubDate: 2021-11-01
  DOI: 10.1134/S1819714021060038
Subduction Erosion at Pacific-Type Convergent Margins
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  Abstract: 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.
  PubDate: 2021-11-01
  DOI: 10.1134/S1819714021060087
A Study on the Possibility of the Reactivation of the Fault System in the
Western Part of the South China Sea as a Source of Geological Hazards
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  Abstract: This article summarizes the results of research on the possible reactivation of the fault system in the Earth’s crust of the South China Sea with likely dangerous consequences for the coastal area of Vietnam. The research was carried out over several years with the publication of interim results. The solution to this problem required the determination of the regional stress field in the Earth’s crust. Analysis of the focal mechanisms of local earthquakes, as well as the structural characteristics of faults obtained by gravity and seismic data was used. The possibility of renewal of fault activity was determined by the inversed-stress method in the calculated regional stress field. The parameters of the present-day stress field were used to estimate the required slip force along the pre-existing faults. The possibility of horizontal and vertical structural (block) displacements in the Earth’s crust of the study area was calculated to assess the probability of reactivation of the entire system of faults. Based on a comprehensive analysis of the data, a forecast of the probability of reactivation of the fault system in the South China Sea has been made. This could be the cause of earthquakes, underwater landslides, and other dangerous natural processes in the coastal area of Vietnam.
  PubDate: 2021-11-01
  DOI: 10.1134/S1819714021060099