GEOLOGICAL SETTING AND GENESIS OF THE KURMANSKY GABBRO-TRONDHJEMITE MASSIF (MIDDLE URALS)

This paper reports the results of petrogeochemical studies of the Kurmansky gabbro-trondhjemite massif (eastern slope of the Middle Urals), lying in the western part of the large Reftinsky allochthonous block within the accretion East Uralian megazone. The relevance of this study is determined by the uncertainty in geodynamic setting and formation conditions of the rock massif and its role in the evolution of the Ural Mobile belt. We specified the countours of the massif. It is shown that the rocks were resulted from spatiotemporal convergence of partial melting in the mantle and lower crust at the island-arc stage of the Ural Mobile belt evolution. Partial melting of mantle peridotite, under the influence of an aqueous fluid rising from the subduction zone, initiated the occurrence of basite melts. The separation of the melt and its subsequent evolution to the compositions of gabbrodiorite and diorite took place at Ptot=10 kbar. Trondhjemites were formed as a result of partial melting of amphibolites at Ptot≥8 kbar, PH2O=0.1–0.2 kbars. The crystallization of trondhjemites in the crust was accompanied by the wollastonite skarns on contact with carbonate rock and xenoliths culminated at mesoabyssal level, Ptot=PH2O=1 kbar. The comparison between the composition of Kurmansky gabbro-trondhjemite massif and the island-arc- and collision-related magmatic suites in the region allowed us to assume that the Kurmansky massif belongs to the independent Early Devonian (?) gabbro-trondhjemite complex of island arc origin. The rock metamorphism conditions were evaluated, with the transformations supposedly related to the accretion of early island arc complexes at the Murzinsky-Aduysky microcontinent, which took place in the Devonian

ГЕОЛОГИЧЕСКАЯ ПОЗИЦИЯ И ГЕНЕЗИС КУРМАНСКОГО ГАББРО-ТРОНДЬЕМИТОВОГО МАССИВА (СРЕДНИЙ УРАЛ)

This paper reports the results of petrogeochemical studies of the Kurmansky gabbro-trondhjemite massif (eastern slope of the Middle Urals), lying in the western part of the large Reftinsky allochthonous block within the accretion East Uralian megazone. The relevance of this study is determined by the uncertainty in geodynamic setting and formation conditions of the rock massif and its role in the evolution of the Ural Mobile belt. We specified the countours of the massif. It is shown that the rocks were resulted from spatiotemporal convergence of partial melting in the mantle and lower crust at the island-arc stage of the Ural Mobile belt evolution. Partial melting of mantle peridotite, under the influence of an aqueous fluid rising from the subduction zone, initiated the occurrence of basite melts. The separation of the melt and its subsequent evolution to the compositions of gabbrodiorite and diorite took place at Ptot=10 kbar. Trondhjemites were formed as a result of partial melting of amphibolites at Ptot≥8 kbar, PH2O=0.1–0.2 kbars. The crystallization of trondhjemites in the crust was accompanied by the wollastonite skarns on contact with carbonate rock and xenoliths culminated at mesoabyssal level, Ptot=PH2O=1 kbar. The comparison between the composition of Kurmansky gabbro-trondhjemite massif and the island-arc- and collision-related magmatic suites in the region allowed us to assume that the Kurmansky massif belongs to the independent Early Devonian (?) gabbro-trondhjemite complex of island arc origin. The rock metamorphism conditions were evaluated, with the transformations supposedly related to the accretion of early island arc complexes at the Murzinsky-Aduysky microcontinent, which took place in the Devonian.В статье представлены результаты петрогеохимических исследований пород Курманского габбро-трондьемитового массива (восточный склон Среднего Урала), залегающего в западной части крупного Рефтинского аллохтонного блока, локализованного в пределах Восточно-Уральской мегазоны аккреционной природы. Актуальность исследований заключается в установлении геодинамических режимов формирования пород, их позиции в эволюции Уральского подвижного пояса. В ходе исследования уточнены контуры массива. Показано, что данные породы образовались в результате сближенных по времени и в пространстве процессов частичного плавления в мантии и нижней коре на островодужном этапе развития Уральского подвижного пояса. Частичное плавление мантийного перидотита под воздействием восходящего из зоны субдукции водного флюида привело к зарождению базитового расплава. Отделение расплава и его последующая эволюция до составов габбро-диорита, диорита происходили при Pобщ=10 кбар. Трондьемиты, ассоциированные с габброидами, были получены в результате частичного плавления амфиболитов при Pобщ≥8 кбар, PH2O=0.1–0.2 Pобщ. Их становление в коре сопровождалось развитием волластонитовых скарнов на контактах с ксенолитами карбонатных пород и завершилось в мезоабиссальной обстановке при Pобщ=PH2O=1 кбар. Выполнено сопоставление состава слагающих массив пород с развитыми в районе магматическими образованиями островодужной и коллизионной стадий, что позволило высказать предположение о принадлежности Курманского массива к самостоятельному раннедевонскому (?) габбро-трондьемитовому комплексу островодужной природы. Охарактеризованы условия метаморфизма пород массива, высказано предположение о связи этих преобразований с аккрецией раннеостроводужных комплексов на Мурзинско-Адуйский микроконтинент, имеющей место в девоне

Венд‐раннекембрийские граниты Крутореченского комплекса (Присалатимская зона, Северный Урал): возраст протолита, геодинамические условия образования и преобразования

The Main Uralian fault (MUF) zone is a suture at the junction of the Urals and the East European platform (EEP). Its complex tectonic melange is still poorly studied. We obtained new data on compositions and ages of the Krutorechensky granites (KG) composing an intensely tectonized and boudinaged elongated body discovered in meta‐ terrigenous and meta‐volcanogenic rocks in the western part of the MUF zone. In chemical composition, these gra‐ nites are similar to the Vendian‐Cambrian collisional granitoids of the Isherim and Lyapin blocks. The LA‐ICP‐MS method was used to determine U‐Pb zircon ages for the KG samples. The zircons contain ancient xenogenic cores (1221–1034 Ma) and young rims (400±6 Ma). The Middle Riphean ages of zircons from the protolith suggest that the KG block (belonging to the Prisalatim zone and located west of the MUF zone) is a fragment of the EEP, because the complexes of the Ordovician‐Devonian Tagil paleo‐island arc (located further eastward) are mostly dated to the Ven‐ dian. The KG crystallization age (537±2 Ma) is practically the first (Vendian) early Cambrian dating for the granites sampled in the MUF zone. Considering this age and the petrogeochemical features, there are grounds to suggest that the Krutorechensky granites originated due to tectonic‐magmatic events (with possible pluming) that took place at the final stage of the Timan collision, similar to granites of the western slope of the Northern Urals (Moiva, Posmak and Velsov massifs). Subsequently, these granites were involved in the Paleozoic accretion‐collision processes that created the modern MUF zone (i.e. tectonic melange). Our study results are important for clarifying the structure of the Urals‐EEP junction zone and useful for geological mapping and metallogenic assessment of the region.Строение зоны Главного Уральского разлома (ГУР) – шовной (сутурной) области на стыке Урала и Восточно‐Европейской платформы – до сих пор изучено довольно слабо, поскольку она является сложно построенным тектоническим меланжем. Нами получены новые данные о составе и возрасте гранитов крутореченского комплекса (КГК), слагающих интенсивно тектонизированное и будинированное удлиненное тело среди метатерригенных и метавулканогенных пород в западной части зоны ГУР. По химическому составу граниты сходны с венд‐кембрийскими коллизионными гранитоидами Ишеримского и Ляпинского блоков. Методом LA‐ICP‐MS получен U‐Pb возраст цирконов из гранитов КГК. В цирконах присутствуют древние ксеногенные ядра (1221–1034 млн лет) и молодые каймы (400±6 млн лет). Среднерифейские датировки в цирконах, заимствованных из протолита, позволяют предполагать, что блок, сложенный гранитами КГК, относящийся к Присалатимской зоне и расположенный западнее ГУР, может быть фрагментом ВЕП, поскольку в комплексах ордовикско‐девонской Тагильской палеоостровной дуги, находящейся восточнее, наиболее часто встречающийся возраст субстрата преимущественно вендский. Возраст кристаллизации гранитов КГК (537±2 млн лет) – это практически первая (венд) раннекембрийская датировка для гранитов в контурах зоны ГУР. Данный возраст и петрогеохимические особенности указывают на генерацию гранитов КГК в ходе тектоно‐магматических событий завершающего этапа Тиманской коллизии подобно гранитам западного склона Северного Урала (Мойвинский, Посьмакский, Велсовский массивы), возможно, при участии плюма. Впоследствии граниты КГК были вовлечены в палеозойские аккреционно‐коллизионные процессы, создавшие современный облик зоны ГУР (тектонический меланж). Результаты важны для уточнения строения зоны сочленения Урала с ВЕП, применяются для целей геологического картирования и металлогенических оценок

ПАЛЕОЗОЙСКИЙ ГРАНИТОИДНЫЙ МАГМАТИЗМ УРАЛА КАК ОТРАЖЕНИЕ ЭТАПОВ ГЕОДИНАМИЧЕСКОЙ И ГЕОХИМИЧЕСКОЙ ЭВОЛЮЦИИ КОЛЛИЗИОННОГО ОРОГЕНА

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.Уральский подвижный пояс является внутриконтинентальным эпиокеаническим орогеном, прошедшим все этапы геодинамического развития. Магматические породы, сформированные в ходе каждого из них, – важное звено для понимания эволюции структуры и определения потенциальной рудоносности ее составных частей. Проведено обобщение большого набора петрогеохимических и изотопно-геохронологических данных по палеозойским (490–250 млн лет) гранитоидам, сопровождающим открытие и эволюцию Уральского палеоокеана и последующее формирование коллизионного орогена. В результате скорректированы представления о времени ряда тектономагматических событий, уточнены палеогеодинамические обстановки формирования гранитоидов разного состава и генезиса, показана роль процессов мантийно-корового взаимодействия и плюмового фактора при формировании зрелой континентальной коры. Результаты могут быть использованы для целей геокартирования и уточнения перспектив потенциальной рудоносности гранитоидных комплексов разного состава и природы

Petrology of Yaluninogorsk granitoid massive (Alapaevsk-Sukhoi Log porphyry copper zone, Middle Urals)

Yaluninogorsk quartz diorite-trondhjemite massif is situated in Alapaevsk-Sukhoy Log zone of Eastern-Ural High potentially productive for Cu (±Mo) porphyry type of mineralization. The massif is a magma chamber 3 × 2 km under central type volcano. The rocks of massif frame are transformed into propylites, sometimes intensively sulfidized. In this regard the massif is considered as an ore-forming. Petrological study of Yaluninogorsk massif shows, that is formed by holocrystalline rocks of meso-abyssal facies, varying from quartz-gabbro-diorites to tonalities, accompanied by veined trondhjemites. Early mineral phases of quartz diorites consist of augite, basite plagioclase An70-50, titanomagnetite. Late phases are represented by acid plagioclase An30-25, quartz, titanomagnetite, biotite, magnesiohornblende, which substitutes pyroxene. Crystallization process of quartz diorites and trondhjemites occurred under isobaric conditions with 1.5-2.0 kbar and a slow cooling. Crystallization temperature exceeded 900°C for the early phases, and 800-720°С for the late phases. The initial melts can be characterized as having low water content. Their oxidation rate was ΔNNO = 0.5-0.8. Residual melts with trondhjemite composition contained about 3.5-4.0 wt % H2O under Pgen = PH2O. Deep erosion of the volcano together with low water content of the initial melts are likely to be negative factors for the discovery of industrial porphyry-type ore deposits associated with Yaluninogorsk massif. The study of post-magmatic transformations of rocks from the massif and its environs revealed the presence of no industrial significance skarns with magnetite-chalcopyrite-pyrite mineralization, accompanied by nickel sulfides and nickel sulfoarsenides; veined carbonate-quartz-chlorite metasomatites with chalcopyrite mineralization, containing selenium-bearing sulfosalts and Ag, Cu, Bi tellurides

Potentially commercial Alapayevsk-Sukhoy Log porphyry copper zone (the Middle Urals)

NS-trending Alapayevsk-Sukhoy Log zone of porphyry-copper mineralisation in the Middle Urals is located 75 km to the east of Yekaterinburg and extends for 100 km from Alapayevsk to Sukhoy Log towns. Sulphide inclusions in rocks are pervasive, and there are numerous ore manifestations and small deposits. Like the commercial Mikheyevskoye porphyry copper deposit (over 1.7 million tonnes of Cu) in the Southern Urals, the zone is associated with the eastern part of East Urals volcanic megazone. It consists of several ore-producing NS-trending volcano-plutonic belts which represent the tectonic blocks. Rejuvenation from north to south of granitoid magmatism has been identified (U-Pb SHRIMP-II and LA ICP-MS zircon dating) in First magmatic stage (million years): from 412 (diorite-plagiogranodiorite-plagiogranite of Yaluninogorsk massif) to 404-406 (diorite-granodiorite-granite of Altynai-Artyomovsk intrusion), and then to 397 (plagiorhyodacite-porphyre of Shata area). Volumetrically sericitized and sulphidized quartz diorite of East-Artyomovsk massif was probably established during Second magmatic stage (369 ± 39 million years, Rb-Sr dating). All granitoids are of arc-island geochemical type, and have feature near-mantle isotopic signatures: (87Sr/86Sr)t = 0.7038-0.7049, (εNd)t = 6.6-8.7. Systemic and comprehensive study of Alapayevsk-Sukhoy Log zone should result in discovery of commercial large scale porphyry copper deposits (assuming current cut-off grade of Cu 0.15-0.20 wt %). The most attractive in terms of potential for high capacity stockworks is the East Artyomovsk massif which is similar in many respects to ore-magmatic system of Mikheyevsk deposit

Vendian – Early Cambrian granites of the Krutorechensky complex (Northern Urals, Russia): protolith age, geodynamic conditions of generation and transformation

The Main Uralian fault (MUF) zone is a suture at the junction of the Urals and the East European platform (EEP). Its complex tectonic melange is still poorly studied. We obtained new data on compositions and ages of the Krutorechensky granites (KG) composing an intensely tectonized and boudinaged elongated body discovered in meta‐ terrigenous and meta‐volcanogenic rocks in the western part of the MUF zone. In chemical composition, these gra‐ nites are similar to the Vendian‐Cambrian collisional granitoids of the Isherim and Lyapin blocks. The LA‐ICP‐MS method was used to determine U‐Pb zircon ages for the KG samples. The zircons contain ancient xenogenic cores (1221–1034 Ma) and young rims (400±6 Ma). The Middle Riphean ages of zircons from the protolith suggest that the KG block (belonging to the Prisalatim zone and located west of the MUF zone) is a fragment of the EEP, because the complexes of the Ordovician‐Devonian Tagil paleo‐island arc (located further eastward) are mostly dated to the Ven‐ dian. The KG crystallization age (537±2 Ma) is practically the first (Vendian) early Cambrian dating for the granites sampled in the MUF zone. Considering this age and the petrogeochemical features, there are grounds to suggest that the Krutorechensky granites originated due to tectonic‐magmatic events (with possible pluming) that took place at the final stage of the Timan collision, similar to granites of the western slope of the Northern Urals (Moiva, Posmak and Velsov massifs). Subsequently, these granites were involved in the Paleozoic accretion‐collision processes that created the modern MUF zone (i.e. tectonic melange). Our study results are important for clarifying the structure of the Urals‐EEP junction zone and useful for geological mapping and metallogenic assessment of the region

VOSTOCHNO-VERKHOTURSKY GABBRO-DIORITE-GRANODIORITE MASSIF (MIDDLE URALS): NEW DATA ON COMPOSITION, FORMATION CONDITIONS, AGE AND METALLOGENY

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 zon

PALEOZOIC GRANITOID MAGMATISM OF THE URALS: THE REFLECTION OF THE STAGES OF THE GEODYNAMIC AND GEOCHEMICAL EVOLUTION OF A COLLISIONAL OROGEN

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