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.

—The Akhunovo–Petropavlovsk area of the late Paleozoic granite magmatism is located in the northeast of the Magnitogorsk megazone (MMZ) in the South Urals. It is a series of successively intruded rocks (Petropavlovsk, Akhunovo, Karagai, and Uiskii Bor intrusions) differing not only in composition, the depth of formation, and ore content but also in the relationship with magmatic and fluid sources and in magma generation mechanisms. This area differs significantly in the number and composition of intrusive complexes from the igneous rocks and ore associations in the central and western parts of the MMZ. The granite magmatism pulses alternated with the collisional shearing/spreading and rifting stages. The Petropavlovsk mesoabyssal granite intrusion (347.0 ± 8.6 Ma) formed at the early stage of the area evolution. Its rocks are similar in composition to a suprasubductional series (melting products of a mantle source enriched not only in water fluid but also in Cl). Later (310–306 Ma), at the collision–compression stage, crustal intrusion of the Akhunovo–Karagai granodiorite–granite complex took place. The intruded rocks are similar to the Middle Urals continental-margin gabbro-tonalite–grano-diorite–granite plutons (320–290 Ma) bearing large gold–sulfide–quartz deposits (Berezovskoe etc.). At the final stage of the area evolution, during the transition from continental-margin regime to hard collision between the East European and Kazakhstan continents (late Carboniferous) and the intense shearing/spreading deformations, the Uiskii Bor granosyenite–granite intrusion (304.0 ± 4.8 Ma) rich in K and HFSE formed. Granite intrusions of this type have been revealed in the MMZ for the first time. Thus, the granitoid complexes of the Akhunovo–Petropavlovsk area formed under changes in geodynamic settings and are characterized by different compositions, depths of occurrence, and genesis. This permits us to consider the area a typical continental-margin center of the long-term mantle–crust interaction, where magma generation proceeded at different mantle and crust levels, with the participation of both suprasubductional and enriched plume-related rift sources.

For the first time, from the standpoint of magmatism and subsequent hydrothermal–metasomatic alteration, sulfide and platinum-metal mineral assemblages of rocks of ore-bearing intrusions of the Khudolaz Complex have been characterized. Four types of assemblages have been identified: (1) pentlandite–chalcopyrite–pyrrhotite in the form of drop-shaped and interstitial disseminations with inclusions of sperrylite, moncheite, michenerite, merenskyite, froodite; (2) complex amoebalike inclusions with the composition pyrite ± pyrrhotite–chalcopyrite–violarite ± pentlandite with inclusions of Sb–michenerite, sudburyite, and borovskite; (3) newly formed pyrite–chalcopyrite veins and patches in intensely metasomatized rocks; (4) additionally-formed euhedral pyrite disseminations in metasomatites along zones intersected by dolerite dikes. The formation of these sulfide–platinum-metal assemblages occurred in three stages: (1) magmatic and late magmatic (type 1), 2) hydrothermal–early medium temperature and late low-temperature (types 2, 3), (3) repeated hydrothermal–low–medium temperature (type 4). It is shown that the crystallization of sulfide minerals occurred in a wide temperature range (about 1000–200°C). PGE minerals separated at the late magmatic stage during cooling of a highly fractionated sulfide or immiscible chalcogenide melt and during decomposition of sulfide solid solutions (T ~ 650–300°C). At the early hydrothermal stage (T ~ 300–250°C), pyrrhotite was replaced by pyrite; pentlandite, by violarite; a significant amount of Ni and Co from primary sulfides was inherited by secondary sulfides. Primary chalcopyrite was mainly replaced by silicates (chlorite, amphibole, etc.). It is suggested that the antimony minerals of Pd (including high-antimony michenerite with Sb up to 0.46 apfu) could have crystallized from an Sb-enriched hydrothermal fluid. Host rocks could have been an additional source of antimony in the fluid. At the late hydrothermal stage (T < 200°C), significant dissolution of primary sulfide and platinum-metal phases occurred with redeposition in the upper parts of massifs and in host rocks. The recurring hydrothermal process (T ≤ 200°C) was associated with emplacement of dikes of the Ulugurtau complex and new redeposition of sulfides along zones of fluid action.

The oceanic stage in the history of the South Urals completed in the Ordovician – Early Silurian. The Ordovician through Devonian events in the region included the formation of an island arc in the East Ural zone from the Middle Ordovician to Silurian; westward motion of the subduction zone in the Late Silurian – Early Devonian and the origin of a trench along the Main Ural Fault and the Uraltau Uplift; volcanic eruptions and intrusions in the Magnitogorsk island arc system in the Devonian. The Middle-Late Paleozoic geodynamic evolution of uralides and altaides consisted in successive alternation of subduction and collisional settings at the continent-ocean transition. The greatest portion of volcanism in the major Magnitogorsk zone was associated with subduction and correlated in age and patterns of massive sulfide mineralization (VMS) with Early – Middle Devonian ore-forming events in Rudny Altai. Within-plate volcanism at the onset of volcanic cycles records the Early (D 1 e 2 ) and Middle (D 2 ef 2 ) Devonian slab break off. The volcanic cycles produced, respectively, the Buribay and Upper Tanalyk complexes with VMS mineralization in the Late Emsian; the Karamalytash complex and its age equivalents in the Late Eifelian – Early Givetian, as well as the lower Ulutau Formation in the Givetian. Slab break off in the Late Devonian – Early Carboniferous obstructed the Magnitogorsk island arc and supported asthenospheric diapirism. A new subduction zone dipping westward and the Aleksandrovka island arc formed in the Late Devonian – Early Carboniferous. The Early Carboniferous collision and another event of obstructed subduction led to a transform margin setting corresponding to postcollisional relative sliding of plates that produced another slab tear. Postcollisional magmatism appears as alkaline gabbro-granitic intrusives with related rich Ti-magnetite mineralization (C 1 ). Transform faulting persisted in the Middle Carboniferous through Permian, when the continent of Eurasia completed its consolidation. The respective metallogenic events included formation of Cu-Ni picritic dolerites (C 2–3 ), as well as large-scale gold and Mo-W deposits in granites (P 1–2 ).

Research subject. The article sets out to investigate the change of the geodynamic regime from the island-arc type to the accretionary-collisional type in the Late Devonian–Early Carboniferous, which occurred as a result of 1) a collision between the Western part of the Magnitogorsk island arc and the Eastern margin of the East European continent and 2) its later coupling with the heterogeneous composite East Uralian terrain.Materials and methods. The content of petrogenic elements and microelements in the rocks of the Late Paleozoic island-arc complexes of the Magnitogorsk island arc were determined using XRF and ICP MS methods at the Laboratory of Physicochemical Research Methods of the Institute of Geology and Geochemistry, Ural Branch of the Russian Academy of Sciences. In addition, available publications on the composition and formation conditions of these complexes were reviewed.Results. It was found that, in the Late Devonian–Early Carboniferous period, the process of island-arc magmatism of the Magnitogorsk paleoarc was substituted with the formation of intraplate volcano-intrusive complexes. The island-arc magmageneration and its manifestations were controlled by a latitudinal linear zoning and different depths of formation of magmatic cameras, reflecting the self-consistency and spatial isolation of these events.Conclusion. Due to the intensifying collision, melts from different mantle sources were mixing, thus contaminating the island-arc rocks by intraplate (plume-dependent) magmas. According to the composition and concentrations of high-field strength and fluid-mobile chemical elements, suprasubductional fluids played an important role in the evolution of late-island arc magmatic series.

АХУНОВО-ПЕТРОПАВЛОВСКИЙ ГРАНИТОИДНЫЙ АРЕАЛ КАК ОКРАИННО-КОНТИНЕНТАЛЬНЫЙ ЦЕНТР ДЛИТЕЛЬНОГО МАНТИЙНО-КОРОВОГО ВЗАИМОДЕЙСТВИЯ: РОЛЬ СУБДУКЦИОННЫХ И РИФТОГЕННО-ПЛЮМОВЫХ ИСТОЧНИКОВ В.В.Холоднов 1 , Е.С.Шагалов 1, 2 , Г.А.Каллистов 1 , Г.Ю.Шардакова 1, 2 , Д.Н.Салихов 3 , Е.В.Коновалова 1 1 ФГБУН Институт геологии и геохимии им.академика А.Н.Заварицкого Уральского отделения Российской академии наук, e-mail:

Subject. A systematization of Late-Paleozoic magmatic formations of the Magnitogorsk zone of the Southern Urals in the process of an accretion of the Magnitogorsk paleoarc to the margin of the East European continent (EEC) with formation in Famenian and Carboniferous active continent margin of South-Uralian accretionary-collisional belt was given in the work.Materials and methods. A generalization of published and manuscript materials characterizing magmatism and ore-mineralization of Magnitogorsk zone for the Devonian-Carboniferous-Permian time carried out, additional investigations of chemical composition of rocks (XRF, ISP-MS) characterizing process of accretion, subduction and plume activity, microelement distribution in them was made, the composition of rock-forming and accessory minerals (EPMA) was studied.Results. It is found that the South-Uralian accretionary-collisional belt was beginning to form in the late phase of the development of the Magnitogorsk island arc in the process its collision with EEC margin with formation in the Frasnian and Carboniferous of active continental margin. The products of Late-island-arc volcanism are represented by the porphyrite formation and in the eastern frame of the arc - by subalkaline monzonite-shoshonite-latite volcanic-intrusive association with intermediate characteristics between the subductional and interplate formations. Synchronously with them, in the backarc setting, picrite and meymechite volcanics − derivatives of a mantle plume are formed. In process of substitution of tectonic-magmatic regime from island-arc to margin-continental intraplate-type mantle series were forming. During this period, hot asthenospheric diapirs (plumes) were rising to the bottom of new-formed (accreted) margin-continental lithosphere. Along with the magmatic associations of intraplate type and rock series of intermediate geochemical type, this geodynamic situation in the Southern Urals is characterized by a presence of great volumes of mantle-crust granitoids of gabbro-tonalite-granodiorite-granite type, that were formed with a manifold manifestation of anatexis in a time interval of 365-290 Ma.Conclusion.On the whole the originality of Magnitogorsk zone geological history in the Devonian and Carboniferous, peculiarities of magmatic complexes formed here due to various geodynamic settings, are making this zone an extraordinary interesting and important object to study of processes of plume-lithosheric and mantle-crust interaction.

ГЕОХИМИЧЕСКИЕ ОСОБЕННОСТИ МЕЖПЛИТНОГО ПЛЮМ-ЗАВИСИМОГО МАГМАТИЗМА МАГНИТОГОРСКОЙ ЗОНЫ ЮЖНОГО УРАЛА В ПОЗДНЕМ ДЕВОНЕ, КАРБОНЕ И РАННЕЙ ПЕРМИ© 2019 г

Forms of occurrence of platinum (sperrilite, moncheite) and palladium (Sb-michenerite, Pd–Bi phase) minerals in intrusive rocks of the Khudolaz differentiated complex have been studied. Platinum minerals were identified in disseminated Cu–Ni sulfide ores from ultramafic olivine–hornblende rocks of the Khudolaz complex, whereas palladium minerals were found in ores from olivine–hornblende gabbroids. The structural arrangement of grains as inclusions in sulfides of the primary magmatic association testifies that they were formed as a result of segregation of platinum group elements, which partitioned into the composition of sulfides during low-temperature mineral formation process at the late-magmatic stage.

АКЦЕССОРНЫЕ АПАТИТЫ ИЗ ГАББРОИДОВ ПОЗДНЕГО ДЕВОНА -РАННЕГО КАРБОНА ЗАПАДНО-МАГНИТОГОРСКОЙ ЗОНЫ: ОСОБЕННОСТИ МОРФОЛОГИИ И ХИМИЧЕСКОГО СОСТАВА, ИНДИКАТОРНАЯ МЕТАЛЛОГЕНИЧЕСКАЯ РОЛЬ © 2018 г.И. Р. Рахимов, В. В. Холоднов, Д

The South-Ural accretion-collision fold belt began to form at the final stage of the island-arc development of the Urals. This process correlates in time with the Famennian and Early Tournasian. During the Carboniferous, the subsequent inversion from the island-arc tectono-geodynamic regime to the accretion-collision and transformed shear-riftogenous ones resulted in a considerable increase in diversified magmatic products. We can observe an intricate spatial and temporal combination of magmatic complexes differing in primary sources and genesis of mantle, mantle-crust and essentially crust anatectic magmatic complexes. The existence of the intraplate-type mantle series is associated with the destruction of the subducting oceanic plate and the rise of hot astenospheric diaper plumes up to the basement of the newly-formed lithosphere. The intrusive gabbro-granite magmatism of that time corresponds to the highest chlorine content and the formation of large-scale magnetite skarn mineralization. Along with the intraplate-type magmatic associations and rock series with intermediate features, this geodynamic setting is also characterized by a considerable amount of mantle-crust granitoids of the gabbro-tonalite-granodiorite-granite (GTGG) type formed with multiple manifestations of supra-subduction and crust (lowermost) anatectic processes. For these stages in the formation of the Hercynian South-Ural orogen, we have established a number of tectono-magmatic stages characterizing the magmatism of such tectonic events that accompanied the attachment of the Magnitogorsk Palaeo Arc and the eastward heterogeneous accretion assemblage to the margin of the East European Plate. Another goal of this paper is to typify the Permian granitoid magmatism, where mantle-crust gabbro-montzodiorite-granite latitic (282-274 Ma) and crust-palingenous granitic (290-276 Ma) and leucogranites (275-260 Ma) series were synchronously formed.

The South-Ural accretion-collision fold belt began to form at the final stage of the island-arc development of the Urals. This process correlates in time with the Famennian and Early Tournasian. During the Carboniferous, the subsequent inversion from the island-arc tectono-geodynamic regime to the accretion-collision and transformed shear-riftogenous ones resulted in a considerable increase in diversified magmatic products. We can observe an intricate spatial and temporal combination of magmatic complexes differing in primary sources and genesis of mantle, mantle-crust and essentially crust anatectic magmatic complexes. The existence of the intraplate-type mantle series is associated with the destruction of the subducting oceanic plate and the rise of hot astenospheric diaper plumes up to the basement of the newly-formed lithosphere. The intrusive gabbro-granite magmatism of that time corresponds to the highest chlorine content and the formation of large-scale magnetite skarn mineralization. Along with the intraplate-type magmatic associations and rock series with intermediate features, this geodynamic setting is also characterized by a considerable amount of mantle-crust granitoids of the gabbro-tonalite-granodiorite-granite (GTGG) type formed with multiple manifestations of supra-subduction and crust (lowermost) anatectic processes. For these stages in the formation of the Hercynian South-Ural orogen, we have established a number of tectono-magmatic stages characterizing the magmatism of such tectonic events that accompanied the attachment of the Magnitogorsk Palaeo Arc and the eastward heterogeneous accretion assemblage to the margin of the East European Plate. Another goal of this paper is to typify the Permian granitoid magmatism, where mantle-crust gabbro-montzodiorite-granite latitic (282-274 Ma) and crust-palingenous granitic (290-276 Ma) and leucogranites (275-260 Ma) series were synchronously formed.

The Irendyk formation is wide spread in the West-Magnitogorsk zone. It extends in submeridional direction continuously from the border of the Orenburg region to the latitude of Miass city. The previous researchers compare Irendyk volcanic rocks with modern island arcs. According to petrogeochemical data of the Irendyk basalts the authors are attributed them to two types nearly equal to island arc and intraplate mantle.

The Irendyk formation is wide spread in the West-Magnitogorsk zone. It extends in submeridional direction continuously from the border of the Orenburg region to the latitude of Miass city. The previous researchers compare Irendyk volcanic rocks with modern island arcs. According to petrogeochemical data of the Irendyk basalts the authors are attributed them to two types nearly equal to island arc and intraplate mantle.

New data on the concentrations of gold and platinum group elements (PGE) in sulfide deposits of the Southern Urals show that a substantial share of Au, Pt, and Pd is concentrated during technological ore processing in their dressing tailings. The behavior of Pt, Pd, and, partly, Au is determined by the size of individual mineral particles.

The paper considers the products of volcanism and intrusive magmatism within the Magnitogorsk-Bogdanovka Graben during the Carboniferous collision stage of the South Urals development. The initiation of the Graben formation and the onset of volcanism occurred during a transpressional regime above the main zone of arc–continent collision at the Early/Late Tournaisian boundary. Volcanic activity manifested itself uninterruptedly from the start of Late Tournaisian to the end of Late Visйan shifting gradually from the south to the north. Based on new geochemical data, we have found that basic volcanites are arranged in two spatially separated associations: 1) high-titanium K/Na tholeites and subalkali basalts controlled by tension fault zones, and 2) K/Na calc-alkali basalts, basaltic andesites and partly andesites with moderate titanium contents that manifested themselves on the tension fault shoulders and were associated with the eruptions of central-type volcanoes. Acid volcanism is represented mainly by rhyolites, trachy-rhyodacites and pantellerites that manifested themselves most intensely in the eastern parts of the Graben. At the end of the Late Visйan the region was activated again due to the involvement of the Kazakhstan Continent into collision. As a result, gabbro-granite magmatism took place and its distribution area was not confined by Magnitogorsk-Bogdanovka Graben. The time of formation gabbro-granite massifs of the Magnitogorsk Series ranged from 340 to 315 MA. The latter age corresponds to isotopic dating of the rhyolite porphyry dike intersecting alkali granites of the Cheka Massif. New geochemical evidence makes it possible to subdivide gabbroids into the Kuybasovsky and Bogdanovsky types (complexes) and granitoids which are represented by six types combined into three petrological complexes, namely, Uzyan, Zhos-Gusikha and Karabulak-Bogdanovka.