Volcano-plutonic Belt Research Articles

Geological Features of Volcanic Rocks of the Lower Taiga Ore Area (Russia, Primorsky Krai)

This article is about features of geological structure and composition of volcanic and sedimentary rocks of the Low Taiga area (Russia, Primorsky region). This area is a part of the east Sihote-Alin volcanoplutonic belt, is located in the area of transit from the continent to the ocean. Studings of geological and chemical composition, structure and patterns of placement of the Low Taiga Area’s volcanic sedimentary rocks allow us to complete information about geological and geochemical features of Mesozoic-Cenozoic stage of the formation of the said structure. Unever igneous formations are distributed within this area, classified to Primorsky (turonian senonian), Samarga (maastrichtian), Bogopolsky (Paleocene) and Kizinsky (Miocene) volcanic complexes. Matching volcanic rocks complex’s chemical composition with published data testifies to significant similarity with petrotypes of ternei volcano structure. Besides it was found that the Low Taiga Area’s complexes contain high potassium varieties and vary in contents of rare and rare earth elements. Distribution of incoherent elements of primorsky complex’s volcanics are characterized by increased concentrations of tungsten, zinc, plumbum, thorium, lanthanum, cerium, by low content of niobium, strontium, zirconium and titanium. Samarga complex is characterized by low content of titanium and strontium, by low content of neodymium. Bogopolsky and Kizinsky complexes in the distribution of rare and trace elements have a similar trend appearance with petrotypes, but differ in the level of their concentration.

First Data on Isotopy and Mineralogical Features Ores Kumirnogo Silver Deposit (Russia, Primorsky Region)

Lockated in the noth part of Primorsky region, the Kumirnoe silver deposit is very interesting object from a geological point of view. Data about isotopic mineralogical characteristics of its ore mineralization was first presented in this essay. More than 80 ore bodies are known at the deposit. They mostly contain quartz, hydromica, sericite, adularia, chlorite, montmorillonite and kaolinite. Ore mineralization is represented by silver-bearing minerals: acanthite, pyrirargyrite, polybasite, stephanite, freibergite, selenium-containing aguilarite and eletrum. The obtained isotope data indicate that sulfur composition is close to meteorite standard, this is indicated by the narrow positive interval of its sulfur ratios (2,0-2,8‰). It gives the reason to assume that homogeneous hydrothermal ore-forming solutions participated in its formation. Its comparison with isotopic data of gold-silver deposits located in the continental marginal volcano-plutonic belts (Ducat, Mnogovershinnoe, Sergeevskoye) shows that the formation of the Kumirnoe deposit was at the same time: Cretaceous- Paleogene, it’s possible it was under similar geological conditions. This is confirmed by the age data obtained by us earlier for Kumirnoe deposit (it matches Cretaceous- Paleogene).

Alkaline granitic magmatism of the Western Transbaikalia: Petrogenetic and geodynamic implications from U-Pb isotopic–geochronological data

The Mongolian–Transbaikalian volcanoplutonic belt extends for almost 2000 km through northern Mongolia and Transbaikalia and hosts several hundreds of plutons of alkali feldspar syenites (AFS) and peralkaline granites (PA) that formed at 280–270 and 230–210 Ma. The giant (~220 km2 in area) Sherbakhta pluton in the Vitim plateau (western Transbaikalia) is located and composed of metaluminous (A/CNK ≤1), high ferroan AFS syenites (10.7–12.3 wt% Na2O + K2O; NK/A < 1) and A-type peralkaline granites (8.7–9.5 wt% Na2O + K2O; NK/A 0.95–1.05). The U-Pb (SHRIMP-RG, LA-ICP-MS) age of the pluton is 260 Ma. The isotope and geochemical characteristics of the studied pluton (ɛNd(T) –2.4 to −2.9; TNd(DM-2) 1.25–1.27 Ga; ɛHf(T) 1.1–0.6, THf(DM-2) 1.02–1.05 Ga, δ18О of quartz 7.3–8.22‰) indicate that the parental trachytic–trachyandesitic melt is compositionally similar to high-Sr syenites of the Sherbakhta pluton and derived by the melting of the mafic, moderately potassium-rich lower crustal source. The magmatic evolution of the parental melt toward a residual ferroan peralkaline granitic melt in the intermediate chamber was controlled by fractional crystallization of sodic plagioclase and K-feldspar, followed by amphibole and aegirine under low oxygen fugacity. The A-type granitoids in the Transbaikalia region formed in the intracontinental geodynamic setting, probably as a result of impact of the mantle plume on heated plastic crust of a young orogen, which formed during the Late Hercynian fold thrust deformations.

U–Th–Pb (SIMS) Dating and Formation Conditions of Volcanic Rocks in the Uyandina–Yasachnaya Volcanic Belt (Northeast Asia, Indigirka Section)

The Uyandina–Yasachnaya volcanoplutonic belt (UYVB) is located in Northeast Asia. As one of the largest volcanic belts in the region, it extends for 900 km from the headwaters of the Kolyma River in the northwesterly direction. The Late Jurassic UYVB overlaps the folds of the Cherskii collision belt. The UYVB rocks are characterized by highly variable facies indicating the heterogeneous nature of the belt. The UYVB has been studied at the cross section of the Indigirka River. This paper reports the first data on U–Pb dating of zircons and the geochemical features of rocks. The concordant U–Pb age of volcanic rocks is 150 ± 2–152 ± 2 Ma (Kimmeridgian–Volgian of the Late Jurassic). It is concluded that the formation conditions of the volcanic rocks change upward through the section, from those typical of mature island arcs to those more typical of active continental margins.

Structural Control of Gold Mineralization of the Central Part of the Malouralsky Volcano–Plutonic Belt (the Polar Urals), Based on an Analysis of Multispectral Images from the Landsat 8 Spacecraft

The central part of the Malouralsky volcanic–plutonic belt, which includes the Manyukuyu–Vorchatinsky ore cluster, is analyzed using multispectral imagery from the Landsat-8 Earth remote sounding satellite with the aim of identifying gold deposits and compared with the Toupugol–Khanmeishor ore region. Similar features in the geological structure and location of deposits and ore deposits in the system of morphological structures are found that should help to develop predictive and prospecting indicators (geological and morphological) of gold mineralization. Three structures are distinguished via analysis of satellite images: the monogenic Novogodnenskaya structure (the Toupugol–Khanmeishorsky ore region) formed under the influence of one main geological process and morphostructures Nos. 1 and 2 (the central part of the Malouralsky volcanic–plutonic belt). These two structures are larger and more complex, with long multistage development. Magmatic chambers are located at depths of ~12 and ~16 km, respectively, for morphostructures Nos. 1 and 2; their root (focal) parts extended southward and then southwestward, respectively, during magmatic development. Prospecting for hydrothermal gold mineralization at the north of the eastern slope of the Polar Urals should be done at the periphery of the centers of large complex morphostructures with long and multistage development with signs of telescoping. Mineralization should be localized in areas of concentration of northwestern and/or northwestern lineaments and in regional fault zones that can be hundreds of kilometers long.

Geochemical, fluid inclusion and O–H–S isotope constraints on the origin of the Rangraz copper deposit, Central Iran

The Rangraz copper deposit (5 Mt @ 0.83% Cu) is located 20 km north of Saveh city, Markazi Province, Iran, in the central Uromieh-Dokhtar volcano-plutonic belt. Host rocks are mainly composed of Eocene volcanic and volcaniclastic rocks that have been intruded by late Eocene quartz monzodiorites and basaltic-andesitic dikes. The dominant copper-related hydrothermal alteration types include silicification, sericitization, and chloritization-kaolinitization. The ore body takes the form of fault-hosted, NW-SE-striking lodes comprising pyrite, chalcopyrite, bornite, specular hematite and magnetite as the principal hypogene ore minerals. Gold (maximum spot assays of up to ca. 0.37 ppm Au) and silver (up to 20.6 ppm Ag) have also been recorded. The ore minerals are mainly confined to veins or veinlets showing crustiform, colloform, open space-filling, dissemination and replacements characteristics in texture. The principal gangue minerals are quartz, barite and calcite. Most of the fluid inclusions identified in quartz-chalcopyrite ± specular hematite veins contain two liquid and vapour phases at room temperature. The primary and pseudo-secondary fluid inclusions have low to intermediate homogenization temperatures between 134 and 338 °C and salinities between 3.55 and 16.89 wt% NaCl equivalents. The fluid inclusion data are consistent with a two-stage evolution of the mineralizing system with initial metal precipitation at crustal depths of <2 km followed by a later pulse of metal deposition at shallower crustal levels of <1 km. The calculated 34SH2S values of sulphide mineral separates from the Rangraz copper deposit range from −9.1‰ to −7.3‰, whereas the calculated δD and δ18O values of the ore fluids range from −3.2 to 0.4‰ and −85 to −75‰, respectively. The δ34S values of the Rangraz samples are consistent with a magmatic sulphur source, implying a possible link between copper mineralization and the Rangraz quartz-monzodiorite. The H, S and O isotope data are consistent with extensive mixing of primary magmatic fluids with cooler, oxidizing meteoric waters occurred in the Rangraz deposit and was responsible for triggering the precipitation of ore minerals. Collectively, the fluid inclusion and isotope data point towards the copper-bearing fluids having been subjected to dilution and cooling, probably as a consequence of their mixing with meteoric waters and boiling. Taken as a whole, the geological setting, ore and gangue mineralogy, vein textures, hydrothermal alteration types, and geochemical, stable isotope, and fluid inclusion evidence may be taken to imply that the Rangraz copper deposit belongs to a class of vein-hosted low sulfidation epithermal mineral systems, several of which have been recorded in the Uromieh-Dokhtar magmatic arc.

Early Paleozoic Protoliths of Gneisses and Granitic Gneisses in the Eastern South Urals: Results of U–Th–Pb (SIMS) Geochronological Studies

The Early Paleozoic age of the protolith for gneisses in the East Uralian megazone (South Urals) is proved by zircon dating. Two metamorphic complexes have been identified in the eastern framing of the Middle–Late Paleozoic Suunduk granitoid pluton. The Zelenodolsk complex is represented by granitic gneisses, while the Kusakan complex (Kusakan Formation) is represented by metavolcanic gneisses, crystalline schists, and quartzites. U–Th–Pb analyses (SHRIMP II) of accessory magmatic zircons from the Zelenodolsk granitic gneiss yielded dates of 478 ± 5 Ma. The protolith age of the Kusakan gneiss (andesitic metatuff) is 529 ± 6 Ma. The origin of volcanic, volcanosedimentary rocks, and granitoids in the East Uralian megazone is associated with the evolution of the volcanoplutonic belt in the active continental margin.

Geochemistry, petrogenesis, zircon U[sbnd]Pb geochronology and Sr[sbnd]Nd isotopic composition of Kuh-e-Shah volcanic rocks: Implications for an active continental margin along with eastern Iran during the Paleogene

The Kuh-e-Shah complex includes the Paleogene volcano-plutonic belt of the Lut Block, eastern Iran. The volcanic rocks which outcropped in this complex mainly consist of trachy-andesites, andesites, and basaltic-andesites that mineralogically contain plagioclase, pyroxene, hornblende, and minor biotite and olivine. Geochemically, they have features typical of high-K calc-alkaline to shoshsonitic magmas with enrichment in large ion lithophile elements (LILE), and depletion in high field strength elements (HFSE) and heavy rare earth elements (HREE). Chondrite-normalized REE plots show enrichment in light REE (4.9 < LaN/YbN < 11.6), Nb depletion and the slight negative Eu anomalies (Eu/Eu* = 0.80–0.99). Tectonic discrimination diagrams are used to infer a volcanic arc setting related to a continental subduction zone. It is concluded that the studied volcanic rocks have resulted from FC of a parental magma which formed by partial melting of the subducted oceanic crust and the overlying mantle wedge with spinel-lherzolite composition. Zircon UPb dating indicates an age of 38.6 to 38.9 Ma for volcanic rocks (Middle Eocene, Bartonian). Initial 87Sr/86Sr and 143Nd/144Nd ratios (0.704350–0.704820 and 0.512619–0.512779, resp.), are compatible with parental melts formation in a subduction mantle wedge. The ɛNdi values (+0.60 to +3.73) are in the range of mantle-derived melts. We suggest that volcanic rocks of the Lut Block are part of the Paleogene volcanism resulted from the Sistan oceanic crust subduction under the Lut Block during the Cretaceous.

Strike-slip fault tectogenesis in formation of the East Sikhote-Alin volcano-plutonic belt: Structural and dynamic analysis

Study object. The role of strike-slip fault tectogenesis in magmatism of the large (North Eastern Primorye) fragment of the Eastern Sikhote-Alin volcano-plutonic belt (ESAVPB) is studied. Materials and methods. The materials of geological mapping and field geostructural thematic-line research are used. Study methods are based on the concept of the geostructural patterns being formed by lateral, namely, strike-slip movements of crustal blocks. Results. There is recognized the system of the NE-trending sinistral faults, whose activation taken place during two stages. The pre-Late-Cretaceous fold-and-strike-slip-fault (orogenic) stage is characterized by the widely developed fold system within the stratified formations covering active strike-slip faults of the pre-Mesozoic consolidated basement. By the Late Cretaceous, the strike-slip faults cut the fold system into narrow blocks, creating the preconditions for the strike-slip faults’ activation during the next destructionand-strike-slip-fault (riftogenic) stage (Late Cretaceous – Cenozoic). During the latter, the strike-slip faults were activated under transtension (strike slip with extension) with formation of volcano-tectonic extension structures (VTES) nearcrosswise the strike-slip faults. The VTES played, on the one hand, the role of magma-feeding channels. On the other hand, the extension caused preconditions for formation of the depression subsidences that accumulated large volumes of the volcanics covering and «crosslinking» the VTES, resulting in wide development of volcanic covers within the ESAVPB. Conclusion. The VTES’ opening is thereby the effect of lateral (strike-slip) displacements of continental geoblocks that is not consistent with a priori ideas of the development of the East Sikhote-Alin volcano-plutonic belt under the oceanic plates’ subduction. The resulting materials complement the formulations according to which the East Asian volcanic belt formed under the structural-and-dynamic conditions being caused by the evolution of the East Asian global strike-slip fault zone resulting from displacement of the Asian continent to the south-west under the Earth’s rotational geodynamics.

Prospecting Fe-Skarn mineralization using ASTER satellite data: case study from Ravanj village, Markazi Province, Iran

The study area is located in Iran central zone and Urumieh-Dokhtar volcanoplutonic belt. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite data was used to identify alteration zones associated with Fe-Skarn mineralization in the Ravanj village, Markazi Province, Iran. Argillic, phyllic and propylitic alteration zones are typically associated with Fe-Skarn mineralization in the study area. In this research, the Selective Principal Component Analysis (SPCA) method was applied to VNIR + SWIR bands of ASTER remote sensing data. Bands 1, 4, 6 and 8 were designated for identification clay minerals. Bands 4, 5, and 6 were selected for argillic alteration mapping. Bands 1, 2, and 4 were used to identification iron oxides/hydroxide minerals. Bands 5, 6, and 7 were chosen to map phyllic alteration zones. Bands 7, 8, and 9 were nominated to specify propylitic alteration mapping. According to the eigenvector statistics calculated using SPCA for ASTER, inverse SPC4 image identified clay minerals and SPC2 images detected argillic alteration, oxides/hydroxide minerals, phyllic alteration and propylitic alteration. In this paper, SPCA technique is an appropriate method because of the distinction between alteartion minerals, vegetation for Fe-Skarn mineralization exploration.

AGE OF THE AMNUNAKTA MONZOGABBRO-MONZODIORITE MASSIF IN THE SOUTHERN FRAMING OF THE SIBERIAN CRATON

The first geochronological data have been obtained for Amnunakta massif composed of monzogabbro-monzodiorite and located in the southeastern part of the Selenga-Stanovoy superterrane. It was found that the age of Amnunakta massif (240 ± 1 Ma) is almost similar to that of quartz porphyry of the Kuitun formation and alkaline granites of the Nerchugan complex, which were sampled from the eastern flank of the Selenga-Vitim Volcano-Plutonic belt. Taking into account the geological position and geochemical features of the Amnunakta massif, there are grounds to suggest that the formation of this massif (as well as of quartz porphyry of the Kuitun formation and alkaline granites of the Nerchugan complex) was associated with one of the impulses of bimodal intraplate magmatism during the evolution of the Selenga-Vitim belt.

Neoproterozoic to Early Triassic tectono-stratigraphic evolution of Indochina and adjacent areas: A review with new data

The Neoproterozoic to Early Triassic tectono-stratigraphic evolution of Indochina and adjacent areas can be divided into six mega-episodes: (1) The Neoproterozoic-Early Cambrian mega-episode was characterized by shallow marine environment in the Sino-Vietnam composite terrane. Meanwhile, the different blocks of the Indochina composite terranes were still separated by branches of the Proto-Tethys. Sino-Vietnam and part of Indochina amalgamated along the Proto-Song Ma suture by the end of the Early Cambrian. (2) During the Middle Cambrian-Early Ordovician mega-episode, shallow shelf carbonate deposition prevailed north of the Proto-Song Ma suture with associated strata containing a rich benthic fauna. This contrasts with deep marine and volcanic arc setting in the south of the Proto-Song Ma suture. (3) The Middle Ordovician-Silurian mega-episode was characterized by subduction of the Tam Ky-Phuoc Son Ocean beneath the Viet-Lao terrane in the north and the Kon Tum terrane in the south. This was followed by a collisional orogeny that sutured the Kon Tum terrane with the Viet-Lao and Viet-Cambodia terranes along the Tam Ky-Phuoc Son suture. The hypothetic Po Ko and Chu Sinh sutures are discussed. The collision led to an intra-continental orogeny in the Sino-Vietnam composite terrane. By the end of the mega-episode, a unified Sino-Vietnam-Indochina super-terrane was established. During the latest Silurian-Early Devonian, benthic fauna and flora of the Sino-Vietnam and Indochina composite terranes shared Cathaysian affinity. (4) The Devonian-Tournaisian mega-episode was characterized by an Early-Middle Devonian transgression and a Late Devonian-Earliest Carboniferous regression, except for parts of northern Indochina where deep marine conditions remained. (5) During the Visean-Middle Permian, the Song Ma ocean reopenned in the north of Indochina. Meanwhile in the west, a volcano-plutonic belt formed due to eastward subduction of the Paleo-Tethys under the Indochina composite terrane. (6) The Late Permian-Early Triassic mega-episode was characterized by Emeishan mantle plume related continental rifting, and the Indosinian orogeny resulting from resuturing of the Indochina and Sino-Vietnam composite terranes along the Song Ma suture.

Strike-slip related tectogenesis and structure-forming flow of crustal masses of the Asia-Pacific transition zone

Research subject. This study was aimed at examining the strike-slip related tectogenesis of the Asia-Pacific transition zone (APTZ).Materials and methods. The research was based on the materials collected by the author during long-term fieldwork across the territories of Primorye, Khabarovsk Krai and, partly,Vietnam. Extensive materials on the topic of the APTZ tectogenesis published by researchers fromRussia,China andJapan were analysed. Investigations involved the study of structural and kinematic assemblages representing the forms, directions and time of crustal mass flows under the strike-slip related tectogenesis of the East Asian global strike-slip fault zone (EAGSSFZ).Results. The EAGSSFZ consists of three transit strike-slip fault systems (zones) playing the role of the APTZ basic deep fault structures. Its master system (MS) is NNE (25–30°) trending longitudinally to theAsia edge. The MS is bordered by diagonal NE 50–70° trending near-continental and meridional near-oceanic EAGSSFZ systems. The MS controls the East Asian volcano-plutonic belt (EAVPB), demarcating the APTZ into internal (near-continental) and external (near-oceanic) zones. Two stages of the strike-slip related tectogenesis were established: orogenic-constructive (Jurassic–to–Late-Cretaceous) and riftogenic-destructive (Late Cretaceous–to–Cenozoic). The riftogenic destruction broke the previously formed orogenic foldedthrust structures, thus causing the EAVPB magmatic succession from intracrustal intrusions (Early Cretaceous) to volcanics (Late-Cretaceous-to-Cenozoic). An increase in the crustal destruction during the end of Cretaceous to Cenozoic resulted in the formation of epicontinental sedimentary basins and deep-sea riftogenic depressions of marginal seas. The structure-forming flow of the APTZ crustal masses occurred in the SSW 180–250° direction being opposite and obliquely opposite towards the NNW subduction direction of oceanic plates.Conclusion. The kinematic disconformity as well as the coincidence of the continental crust flow (plate flows) with the direction of inertial-and-equator-oriented forces allowed the author to determine the structuring of the transition zone as a process independent of the geodynamics of oceanic plates and subordinate to the rotational geodynamics of the non-uniformly rotating Earth.

Selenga ore district in Western Transbaikalia: structural and mineragenetic zoning, genetic types of deposits and geodynamic settings of ore localization

Based on complex structural, geological, and mineragenetic metallogenic studies, taking into account the results of earlier subject-specific, prospecting, mapping, and exploration works, it has been established that Upper Paleozoic and Early Mesozoic tectono-magmatic structures are widely developed within the ore district. They are associated with the development of the transregional Upper Paleozoic Selenga-Vitim volcano-plutonic belt of riftogenic type as well as with the formation of the Early Mesozoic Western Transbaikalian zone of intraplate magmatism. The main commercially important mineral raw material resources of the Selenga ore district which are located in the ore clusters (the Kunaley, Kizhinga, Cheremshanka-Oshurkovo, Tashir etal.) and beyond their bounds are associated with the Late Paleozoic-Mesozoic magmatic activity. It is shown that molybdenum and beryllium are the main ore mineral resources within the investigated ore district which establish its mineragenetic features. The new material characteristics of the Upper Paleozoic and Early Mesozoic intraplate magmatic complexes and the associated deposits of mineral raw materials (Mo, Be, Ti, quartz, fluorite and apatite raw materials) and other promising ore objects of gold, uranium and rare-earth-barium-strontium mineralization are obtained. The geodynamic conditions of their formation and the main age boundaries of the ore-forming processes are revealed, the prospects of mining in the Selenga ore district and the involvement of this ore potential in the program of the regions economic modernization are estimated.

Rhenium abundance in molybdenites: a case study on vein-type Cu-Mo-Au mineralisation in the Qarachilar area, Sungun porphyry Cu and Siah Kamar porphyry Mo deposits, NW Iran

The vein-type Cu-Mo-Au mineralisation in Qarachilar, the Sungun porphyry Cu deposit (PCD) and the Siah Kamar porphyry Mo deposit (PMD) are all located at the northwestern end of the Neo Tethys-related Urumieh–Dokhtar volcano-plutonic belt of Iran. Re contents of molybdenite samples from the Qarachilar, Sungun and Siah Kamar deposits are about 112.67–462 ppm, 53.24–252.29 ppm, and 10.44–41.05 ppm, respectively. Re contents of the first two deposits fall in the range of PCDs, while those of the latter are lower and correspond to PMDs. The relatively high Re content of the Qarachilar and Sungun molybdenites can be explained considering the low abundance of molybdenite, a mantle-dominated source for ore materials and the incorporation of oxidized and acidic hydrothermal fluids with high f Cl. The high abundance of molybdenite in the Siah Kamar PMD has resulted in volume dilution of Re. Furthermore, occurrence of the main ore within the potassic alteration zone and, hence, the alkaline nature of the responsible fluids in this zone have also affected the Re content of molybdenites. Variations of the Re content in different veins/veinlets showed a negative relationship with the formation temperature of these veins, and a positive/negative relationship with the acidity/alkalinity of the hydrothermal fluids, while the grain size of molybdenites showed a positive relationship.

Reconstruction of the Vendian–Cambrian active continental margin of the Southern Urals: results of studying of detrital zircon from the Ordovician terrigenous rocks

Detrital zircons of Ordovician terrigenous sequences are studied in various Southern Uralian tectonic units.The age of detrital zircons of the West Uralian and Transuralian megazones, Taganai–Beloretsk Zone, and Kraka allochthons spans from the Late Archean to the end of the Vendian– beginning of the Cambrian; Early Precambrian and Early–Middle Riphean zircons are the most abundant. Vendian–Cambrian detrital zircons are strongly dominant in the Uraltau Zone, Sakmara allochthons, and East Uralian Megazone; the zircons of other ages are absent or extremely rare. The Vendian–Cambrian detrital zircons of all Southern Urals zones probably derive from volcanic and granitic rocks of the marginal continental belt, which are part of the Uraltau Zone, Sakmara allochthons, and East Uralian Megazone. The Lu–Hf isotopic characteristics of Vendian–Cambrian detrital zircons indicate that their parental rocks formed on a heterogeneous basement that includes blocks of juvenile and ancient continental crust. According to a model of the pre-Ordovician tectonic evolution of the Southern Urals, at the end of the Late Riphean, the passive margin of the East European Platform collided with a block on a heterogeneous basement. The formation of the block terminated with the Grenville Orogeny. After collision, a volcano-plutonic belt originated in the Vendian–Cambrian at the actively evolved margin of the East European Platform.

Late Permian to Early Triassic back-arc type volcanism in the southern Mongolia volcano-plutonic belt of the Central Asian Orogenic Belt: Implication for timing of the final closure of the Palaeo-Asian Ocean

We investigated alkali series volcanic rocks newly discovered in the southern Mongolia volcano-plutonic belt of the Central Asian Orogenic Belt (CAOB) and classified as basalt, basaltic trachyandesite, andesite, trachyandesite, and trachyte, mainly showing andesitic-dacitic compositions. In Harker diagrams, the TiO2, FeO, MnO, Al2O3, CaO, and MgO contents generally decrease with increasing SiO2, representing a series of differentiated volcanic rocks. The primitive mantle-normalized trace element spider diagram is characterized by incompatible element-rich patterns and negative Nb anomalies. The tectonic discrimination diagrams show that the volcanic rocks were formed by arc-related volcanism rather than within-plate volcanism. K-Ar dating of feldspars from six volcanic rocks yields ages ranging from 270 to 239 Ma, indicating that andesitic and dacitic magmatism occurred during this period. These geochemical and geochronological data indicate that the differentiated volcanic rocks intruding middle to late Palaeozoic volcanic sediments were formed by back-arc type subduction ca. 270–240 Ma. Based on detrital zircon U-Pb ages, the terrigenous sandstones underlain by the volcanic sediments record a maximum depositional age of Late Triassic (ca. 205 Ma), and abundant detrital zircons of ca. 250–210 Ma imply the Early Triassic felsic volcanism near this region. They also include a main cluster of Early Devonian ages (ca. 440–380 Ma) and Late Carboniferous to Early Permian (ca. 330–280 Ma), possibly derived from the Devonian-Carboniferous arc complex and Early Permian granites observed surrounding this study area. These results from the volcanic and sedimentary rocks in this study, combined with investigations in previous studies, imply that subduction beneath the eastern segments of the CAOB to consume the Palaeo-Asian Ocean continued until Late Permian to Early Triassic.

A Reconstruction of a Vendian–Cambrian Active Continental Margin within the Southern Urals: Results of Detrital Zircons Studying from Ordovician Terrigenous Rocks

Detrital zircons of Ordovician terrigenous sequences are studied in various Southern Uralian tectonic units. The age of detrital zircons of the West Uralian and Transuralian megazones, Taganai–Beloretsk Zone, and Kraka allochthons spans from the Late Archean to the end of the Vendian– beginning of the Cambrian; Early Precambrian and Early–Middle Riphean zircons are the most abundant. Vendian–Cambrian detrital zircons are strongly dominant in the Uraltau Zone, Sakmara allochthons, and East Uralian Megazone; the zircons of other ages are absent or extremely rare. The Vendian–Cambrian detrital zircons of all Southern Urals zones probably derive from volcanic and granitic rocks of the marginal continental belt, which are part of the Uraltau Zone, Sakmara allochthons, and East Uralian Megazone. The Lu–Hf isotopic characteristics of Vendian–Cambrian detrital zircons indicate that their parental rocks formed on a heterogeneous basement that includes blocks of juvenile and ancient continental crust. According to a model of the pre-Ordovician tectonic evolution of the Southern Urals, at the end of the Late Riphean, the passive margin of the East European Platform collided with a block on a heterogeneous basement. The formation of the block terminated with the Grenville Orogeny. After collision, a volcano-plutonic belt originated in the Vendian–Cambrian at the actively evolved margin of the East European Platform.

Magmatic Control of Gold Mineralization in Western Primorye

The article analyzes the regional gravitational field of northeastern China, Korea, and Western Primorye. The distribution of gold deposits is compared with the development of Mesozoic magmatism and negative gravitational field anomalies. Based on an analysis of geological, minerogenic, petrophysical, and geophysical materials, geological and geophysical zoning of the western part of the Khanka massif was carried out and a scheme was compiled for interpreting geological and geophysical data with minerogenic elements. The authors have determined the relationship between magnetic and gravitational field anomalies and the position of prospective gold-bearing ore districts and clusters in the junction zone of the North China Triassic–Jurassic volcanoplutonic belt with Proterozoic substrates of the Khanka massif. Based on geophysical data, early Jurassic intrusions were identified, which controlled the location of gold ore clusters. A conclusion is drawn about the relationship between gold mineralization and Jurassic magmatism, which increases the prospects for discovering gold mineralization in the Prikhankaysky region of Western Primorye.

Геологическое строение и этапы тектонической эволюции палеозоид Казахстана

Research subject. In this paper, we set out to investigate main paleostructures in Kazakhstan. In particular, we attempt to clarify or revise their existing geodynamic structures and to show key stages in their development on the basis of new data on the age of some stratigraphic units and rocks of the ophiolitic association. Materials and methods . The work was based on the materials of long-standing geological research performed by the authors, including government-funded geomapping, tectonic zoning and paleoreconstruction, as well as the revision of literature data. Results . It is shown that the main sedimentary, volcanogenic, volcanogenic-sedimentary and intrusive complexes were originated in the western part of the Central Asian fold belt (Paleozoic Kazakhstan) in place of various structures differing in their geodynamic environment and tectonic history throughout the Proterozoic and entire Paleozoic periods. The Epigrenville microcontinent disintegrated into individual massifs has been described, along with rift depressions, basins with oceanic crust, island arcs and island arc systems, the Epicaledonian continent, continental depressions, regional volcano-plutonic belts and marginal basins . The tectonic zonality of Kazakhstan has been presented in the form of diagrams. The mapping of the Precambrian Ulutau massif has been conducted. The distribution of the Devonian complexes and the Late Paleozoic complexes of Kazakhstan is schematically represented. Conclusions . We have refined and partially revised the existing concepts and tectonic consecution on the territory of Kazakhstan. On the basis of paleoreconstructions, key stages in the development of main paleostructures have been established; features of the geological evolution of Kazakhstan paleozoids and their relationship with tectonic processes in the Central Asian fold belt have been determined. It is shown that the modern structure of Kazakhstan paleozoids was evolving over a long period and in many stages for almost 900 million years.