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The Ural mobile belt is an intracontinental epioceanic orogen that has already gone through all stages of the geodynamic development. Igneous rocks formed during each stage are important indicators for understanding the evolution of this belt and determining potential ore contents of its segments. We consolidated large datasets on petrogeochemistry and isotope geochronology of the Paleozoic (490–250 Ma) granitoids associated with the opening and evolution of the Ural paleoocean and the subsequent formation of the collisional orogen. Using these data, we have revised the ages of several tectono-magmatic events, clarified the paleogeodynamic settings for the generation of granitoids of different compositions, and described the roles of mantle-crust interactions and the plume factor in the formation of the mature continental crust in the study area. The results can be useful for geological mapping and improving the assessment of the potential ore contents in granitoid complexes that differ in origin and composition.

Transformation of the oceanic crust into the continental one in orogenic belts is an important problem in petrological studies. In the paleocontinental sector of the Urals, a key object for tracing the stages of metamorphism and investigating the origin of anatectic granites is the Murzinka-Adui metamorphic complex. We have analyzed trace elements in zircons and established their genesis, sources, crystallization conditions, and stages of metamorphic events and granite generation in this complex. Zircons compositions were determined by the LA-ICP-MS method. Temperatures were calculated from Ti contents in the zircons. We distinguish three geochemical types of zircons, which differ in the ratios of light and heavy REE, U, Th, Ti, Y and show different values of Ce- and Eu-anomalies and Zr/Hf ratios, which are indicative of different crystallization conditions, as follows. Type I: minimal total LREE content; clear negative Eu- and Ce- anomalies; features of magmatic genesis; crystallization temperatures from 629 to 782 °C. Type II: higher contents of Ti, La, and LREE; low Ce-anomaly; assumed crystallization from highly fluidized melts or solutions. Type III: low positive Eu-anomaly; high REE content; low Th/U-ratio; zircons are assumed to originate from a specific fluidized melt with a high Eu-concentration. Ancient relict zircons (2300–330 Ma) in gneisses and granites show features of magma genesis and belong to types I and II. Such grains were possibly inherited from granitoid sources with different SiO2 contents and different degrees of metamorphism. Based on the geological and petrogeochemical features and zircon geochemistry of the Murzinka-Adui complex, there are grounds to conclude that the material composing this complex was generated from the sialic crust. The main stages of metamorphism and/or granite generation, which are traceable from the changes in types and compositions of the zircons, are dated at 1639, 380–370, 330, and 276–246 Ma. Thus, transformation of the oceanic crust into the continental one was a long-term and complicated process, and, as a result, the thickness of the sialic crust is increased in the study area.

—The chemical composition of rocks of the Murzinka–Adui metamorphic complex and the Murzinka granite pluton, a reference interformational granite pluton in the Urals, is considered. A detailed comparative analysis of ancient gneisses and related granite veins included an isotope–geochemical study of zircons from both groups of rocks. Zircons are subdivided into seven age groups (I, 1588 ± 20 Ma; II, 1060 ± 28 Ma; III, 530 ± 11 Ma; IV, 380 ± 6 Ma; V, 330 ± 9 Ma; VI, 276 ± 3 Ma; and VII, 260 ± 3 Ma). The first four groups are apparently zircons from gneisses, reworked to different extents, and the other three groups are zircons crystallized during granite genesis. The gneisses and most of the granite samples contain zircons of all the above age populations, which is evidence of trapping zircons from gneisses by granite melts, on the one hand, and the occurrence of “granite-derived” zircons in gneisses, on the other. The granitoids and gneisses of all types differ considerably in geochemical features. The behavior of trace elements and the Rb–Sr ages indicate that the formation of granites of the Murzinka massif was a discrete episode of magmatic activity. The Sr isotope ratios in the granites and gneisses indicate different degrees of the mantle–crust interaction and the participation of the material of the crystalline basement and newly formed crust in their formation.

The mechanisms and sources of magma generation for the large Permian Aduyskiy granite massif, well known for rare metal, semi-precious stone and molybdenum deposits, are considered. Valuable information was obtained from study of the Kamenskiy and Krutikhinskiy massifs located at the base of Aduyskiy granite body. The migmatites of these two massifs as well as the accompanying partial melting have approximately the same zircon and Rb-Sr age. These processes range about 309-298 Ma in the Kamenskiy and 308-283 Ma in Krutikhinskiy massifs with the main and most intense stage within 296-298 Ma. That time, the main volume of the granite melt for Kamenskiy, Krutikhinskiy, and Aduyskiy massifs was formed. The migmatites of magma generation zone have banded texture in Kamenskiy massif, but, in Krutikhinskiy massif, anatectic melt formed the numerous veins and small intrusive bodies. These magmatic differences were formed mainly due to protolith composition. Камenskiy migmtites are characterized by Devonian – Carboniferous quartz diorites and granodiorites. Predominantly granitic rocks are characteristic for Krutikhinskiy massif. Basic dykes accompanied the migmatization in both massifs.

Relevance of the problem. In the Urals, in connection with the solution of the problem of supplying the operating non-ferrous metallurgy enterprises with local raw materials, a number of copper-porphyry ore-bearing deposits have been involved in the industrial development in the last decade; low-sulfidation mineralization is localized mainly in dioritic intrusive massifs. The presence of large-scale mineralization of native copper in the diorites of the Vostochno-Verkhotursky massif testifies to the need for its comprehensive study and determination of ore-forming appurtenances. Purpose of the paper is to determine the formation and age appurtenances, as well as the metallogenic specialization of the eastern part of Verkhotursko-Isetskaya zone (Middle Urals) of the Vostochno-Verkhotursky massif within which mineralization of native copper was previously identified. Results. Petrographic, geochemical, and isotope-geochronological studies of the gabbro, diorite and granodiorite massifs were carried out (SiO2–53.97–67.32%, K2O – 1.04–2.65%) and gabbro-diorite dikes occurring among them SiO2 – 54.50-56.50%, K2O – 0.96–1.50%). The predominantly corniferous rocks of the massif belong to a single homodromous calci-alkalic normal-alkalic series of a moderately potassic type. Dyorites of dikes are comagmatic to enclosing rocks. The massif is formed in the abyssal-mesoabyssal conditions of the supra-subduction situation at the continental margin of the zone development. The U-Pb age of the investigated rocks of the massif is determined by zircon (the method of laser ablation) in 339.2 2.8 million years (Carbonic period). The formation of the massif occurred within the tectonic block with the basement of the Proterozoic age of the sialic composition. The presence of high concentrations of F in accessory apatites (up to 3.5–4.2%) at relatively low Cl (up to 0.5%) and SO3 (up to 0.4-0.9%) indicates a possible gold-rare metal specialization of formations. Conclusion. To determine conditions for the formation of the mineralization of native copper among the supra-subduction dioritoids of the Middle Carbonic period, its age, ore-bearing belonging, and scale, it is necessary to further study both the formations of the Vostochno-Verkhotursky massif (including those that underwent secondary alterations) and other dioritoid massifs in the eastern part of the Verkhoturskaya-Isetskaya zone

732 A band of layered gabbro intrusions belonging to the Kusa–Kopan Complex is confined to the zone of the Zyuratkul riftogenic fault in the eastern part of the Bashkir Meganticlinorium, where it consists of several massifs (Matkal, Kopan, Medvedevo, Kusa) with the Ryabinovka and Gubenskii granitoid massifs located in the hanging wall (Fig. 1). The gabbro massifs enclose synonymous ilmenite–titanomagnetite deposits of the Urals in the form of stratified series, vein, and lenticu� lar lodes of continuous and disseminated ores, which alternate with gabbroids. These deposits were discov� ered in the 1930s, and since that time their geological structure and composition of ores and host rocks have been studied by many researchers. The primary atten� tion was paid to the most debatable factors responsible for strong lateral variations in the composition of rocks and ores within the complex, represented by horn� blende gabbro and gneiss–granites in the Kusa and Gubenskii massifs and ilmenite–magnetite ores in the Kusa and Medvedevo deposits in the north and by gab� bronorites (Matkal and Kopan massifs), porphyroid granophyric granites (Ryabinovka Massif), and titano� magnetite ores in the south. Some researchers explain such differences in the mineral composition by the influence of superposed metamorphic processes on rocks and ores of the Kusa Massif [1, 2], which occurred substantially after the formation of intru� sions. Our petrological studies performed in recent years revealed that the formation depth of granitoids, gab� broids, and enclosed ores increases along this band in the northerly direction from 3–4 km in the south to 20–30 km in the north. Accordingly, the P–T param� eters of rock and ore formation vary in the same direc� tion: = 0.5–3.0 kbar and T = 900–1100°C in the south (Kopan and Matkal gabbro massifs and associ� ated deposits, Ryabinovka granite massif) and P = 6– 9 kbar and T = 600–900°C in the north (Kusa and Medvedevo gabbro and Gubenskii granite massifs

Gabbro-tonalite-granodiorite-granite (GTGG) plutons productive for gold are suprasubduction intrusive bodies formed at an Andean-type active continental margin 410–380, 365–355, and 320–290 Ma ago. The Devonian plutons are situated in the southeastern marginal continental zone, whereas the Carboniferous plutons occur in the northwestern zone. All GTGG plutons are mantle-crustal. Their formation started with hydrous basic magmatism and was accompanied by such magmatism up to the final stage. Mantle-derived amphibole gabbro and diorite experienced partial melting (anatexis) in the lower crust under a pressure of 6–10 kbar, giving birth to the tonalite-granodiorite members of the GTGG series. The latter, in turn, were involved in anatexis with the formation of adamellite and granite, immediately accompanied by hydrothermal gold mineralization. The multistep anatexis is the main petrogenetic process responsible for the gold resource potential of GTGG plutons. In the process of anatexis occurring under high fluid saturation, gold was repeatedly removed from rocks into fluid, facilitating its concentration in ore deposits.

In recent years extensive data have been obtained on all geologically important intrusive complexes in the Central and Southern Urals by U-Pb zircon geochronologic high spatial resolution techniques (LA ICP MS, NORDSIM, and SHRIMP II). This made it possible to revise the current concepts for the magmatic activity of the Ural Paleozoic orogen.

The main stages of the Paleozoic intrusive magmatism in the Urals, 460–420, 415–395, 365–355, 345–330, 320–315, and 290–250 Ma, as well as two virtually amagmatic periods, 375–365 Ma (Frasnian-early Famennian) and 315–300 Ma (Late Carboniferous), are recognized. The Cambrian-Early Ordovician pause predated the onset of igneous activity in the Ural Orogen, while the Early Triassic pause followed by an outburst of trap magmatism postdated this activity. The interval from 460 to 420 Ma is characterized by mantle magma sources that produced ultramafic and mafic primary melts. The dunite-clinopyroxenite-gabbro association of the Platinum Belt and miaskite-carbonatite association are specific derivatives of these melts. The rift-related (?) Tagil Synform functioned at that time. The volcanic-plutonic magmatism in this oldest magmatic zone of the Uralides comprises gabbro, gabbro-granitoid, and gabbro-syenite series and comagmatic volcanic rocks. After a break almost 20 Ma long, this magmatism ended in the Early Devonian (405–400 Ma) with the formation of small K-Na gabbro-granitoid plutons. The magmatic intervals of 415–395, 365–355, and 320–315 Ma are characterized by the mantle-crustal nature. The first interval accompanied obduction of the oceanic lithosphere on the continental crust. The subsequent magmatic episodes presumably were related to the subduction of the island-arc (?) lithosphere beneath the continent and to the collision. The intense granitoid magmatism started 365–355 Ma ago. As in the following interval 320–315 Ma, the tonalite-granodiorite complexes, accompanied by hydrous basic magmatism, were formed. Amphibole gabbro and diorite served as a source of heat and material for the predominant tonalite and granodiorite. The Permian granitic magmatism had crustal sources. Thus, the mantle-derived Ordovician-Middle Devonian magmatism gave way to the mantle-crustal Late Devonian-Early Carboniferous plutonic complexes, while the latter were followed by the crustal Permian granites. This sequence was disturbed by rifting and formation of continental arcs accompanied by specific Early Carboniferous Magnitogorsk gabbro-granitoid series and Early Permian Stepnoe monzodiorite-granite series, which deviate from the general evolutional trend.

Murzinka and Dzhabyk are continental-type batholiths of the middle and southern East Uralian domain. They comprise mainly undeformed peraluminous K-rich granites whose elemental composition is similar to some late-Variscan granites of western Europe, but with much more primitive Sr and Nd isotope ratios. Murzinka (254±5 Ma) is composed of silica-rich granites forming two different rock series with a 87Sr/86Srinit of 0.709 and 0.704, respectively. Both series have enormous variations in eNd255 (–11.9 to –0.1 and –8.9 to +4.1) that reveal derivation from heterogeneous sources. Dzhabyk (291±4 Ma) also comprises two coeval magmas which yielded voluminous granites and quartz-monzonites, respectively, with smaller differences in 87Sr/86Srinit and eNd290 (~0.7043, +0.8 to +1.6 and ~0.7049, 0.0 to +0.8). Despite their isotope compositions both batholiths lack evidence of genetic involvement of a mantle-derived parental magma. Moreover, we suggest that Dzhabyk granitoids were generated by polybaric partial melting of Paleozoic island-arc material, whereas Murzinka granitoids derived from an extremely heterogeneous source consisting mainly of Paleozoic and Proterozoic metagreywackes. This implies a relative fast reworking of juvenile arc crust and burial of the protoliths during the orogenic evolution of the Urals. Since there is neither evidence of significant extension, nor a direct link with subduction, we suggest that the main cause for late-orogenic anatexis was elevated heat production and fertility in the protolith, perhaps combined with some additional heat from unexposed mafic intrusions.

Using single-zircon stepwise-evaporation 207Pb/206Pb and whole-rock Rb–Sr methods, we have dated the main facies of four Variscan batholiths of the Urals — Syrostan, Verkhisetsk, Murzinka and Dzhabyk — from different geodynamic environments. Syrostan and Verkhisetsk are subduction-related batholiths of the accreted terrains in the west, closely related to the Main Uralian Fault. Syrostan is composed of metaluminous epidote-bearing synkinematic gabbros, diorites and granodiorites (87Sr/86Srinit≈0.7029–0.7035), dated at 333±3 Ma, and postkinematic granites (87Sr/86Srinit≈0.7035–0.7038) dated at 327±2 Ma, whose zircons occasionally have cores with an age of ∼1800 Ma. The presence of these relict zircon cores probably indicates the contribution of Russian Platform materials to subduction-related magmas. Verkhisetsk, 250 km north of Syrostan, comprises deformed amphibole- and epidote-bearing granodiorites (87Sr/86Srinit≈0.7042–0.7044), dated at 318±3 Ma, and undeformed granites (87Sr/86Srinit≈0.7044) that record a long history of recurrent partial melting and crystallization, from ∼310 Ma to ∼275 Ma. Murzinka and Dzhabyk are continental-type batholiths in the east Uralian zone. Dzhabyk, in the southern Urals, postdates the Kartali seismic reflector and is composed of several coeval intrusions of metaluminous monzonites (87Sr/86Srinit≈0.7049) and peraluminous granitoids (87Sr/86Srinit≈0.7043) dated at 291±4 Ma. Murzinka, 600 km north of Dzhabyk, also comprises two coeval intrusions of peraluminous granites with different chemical and isotopic compositions (87Sr/86Srinit≈0.7045 and 0.7093) dated at 254±5 Ma. These data indicate that the age of cessation of movements along the Main Uralian Fault and the transition from subduction to continent–continent collision migrated northwards. The age of granite magmatism also migrated gradually northwards and eastwards, suggesting an oblique convergence with a SE movement of the converging continent, so that the closure of the Uralian palaeo-ocean started in the south and then migrated progressively northwards.

This paper is an attempt to summarize current knowledge of Uralian magmatism, focusing on those aspects relevant for understanding its geodynamic evolution. The Urals consist of three tectonomagmatic domains: a Suture Sector, in the west, and two N–S imbricated Island-Arc Continental Sectors in the east. The Suture Sector comprises lower Palaeozoic mafic-ultramafic complexes which show eastward impoverishment in LILE, thus reflecting the transition of the subcontinental lithospheric mantle of the Russian plate to the suboceanic lithospheric mantle of the subducted Uralian palaeo-ocean. The two Island-Arc Continental Sectors represent the transition from oceanic to continental environments in the middle and south Urals. Collisional magmatism started in the Silurian and persisted till the Permian, migrating progressively eastward and increasing in abundance of LILE and 87 Sr 86 Sr initial . Magmatic polarity is very similar to that of modern subduction zones and indicates that the subducted slab was dipping eastward during that period. The Northern and Southern Island-Arc Continental Sectors show many similarities regarding the nature and spatial-temporal distribution of magmatism, but there are also some important differences which probably indicate somewhat different geodynamic regimes. In the Northern Sector, Carboniferous tonalite-granodiorite batholiths have features compatible with an origin by melting of the oceanic crust in the subducted slab. In the Southern Sector, however, Carboniferous tonalite-granodiorite batholiths have features more consistent with a melting event within the lower continental crust above the subduction zone than with melting within the subducted slab. Upper Carboniferous-Permian granites have high 87 Sr 86 Sr initial in the north (e.g., 0.7120 in the Murzinka batholith) but very low 87 Sr 86 Sr initial in the south (e.g., 0.7045 in the Dzhabyk batholith) in spite of rocks from both batholiths being equally peraluminous and showing evidence of derivation by anatexis of metasediments. The low 87 Sr 86 Sr initial at Dzhabyk might indicate that in the Southern Sector the accretionary prism grew very rapidly, thus allowing involvement in upper Palaeozoic melting events.