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

ЦИРКОНЫ ИЗ ПОРОД МУРЗИНСКО-АДУЙСКОГО МЕТАМОРФИЧЕСКОГО КОМПЛЕКСА (СРЕДНИЙ УРАЛ): ГЕОХИМИЯ, ТЕРМОМЕТРИЯ, ПОЛИХРОННОСТЬ, ГЕНЕТИЧЕСКИЕ СЛЕДСТВИЯ

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.Изучение процесса преобразования океанической коры в континентальную, идущего в орогенных поясах, – важный вопрос петрологии. Мурзинско-адуйский метаморфический комплекс, расположенный в палеоконтинентальном секторе Урала, является одним из ключевых объектов, где можно проследить этапы метаморфизма и сопряженного с ним анатектического гранитообразования. Цель работы – на основе анализа микроэлементного состава цирконов из гнейсов и жильных гранитов данного комплекса установить их генезис, источники, условия кристаллизации, уточнить этапность гранитообразования. Состав цирконов изучался методом LA-ICP-MS, температуры рассчитаны по содержанию титана в цирконе. Выделены три геохимических типа цирконов, различающихся соотношением легких и тяжелых РЗЭ, U, Th, Ti, Y, величинами Zr/Hf-отношения и аномалий Се и Eu, что предполагает разницу в условиях кристаллизации. Цирконы I типа содержат минимальное количество LREE, имеют ясные негативные аномалии Cе и Eu, обладают признаками магматического генезиса. Температура их кристаллизации составляет 629–782 °С. Цирконы II типа имеют более высокие содержания Ti, La, LREE, слабую аномалию Ce. Предполагается их кристаллизация из высокофлюидизированных расплавов или растворов. Цирконы III типа обладают слабой позитивной аномалией Eu, высокой суммой РЗЭ, низким Th/U-отношением и могли образоваться из особого флюидонасыщенного расплава с высокой концентрацией Eu. Древние реликтовые цирконы с широким разбросом возрастов (от 2300 до 330 млн лет) фиксируются в гнейсах и гранитах, имеют признаки магматического генезиса, соответствуя I и II типу. Они могли быть заимствованы из источников гранитоидного состава, имеющих разную основность или в разной степени преобразованных. Особенности строения мурзинско-адуйского комплекса, петрогеохимические параметры пород, геохимия цирконов указывают на сиалическую природу вещества, слагающего данный сегмент земной коры. Главные этапы метаморфизма и/или гранитообразования, которые нашли выражение в смене морфотипов и составов цирконов, отвечают 1639, 380–370, 330 и 276–246 млн лет, т.е. процесс континентализации был длительным, сложным и привел к повышенной мощности сиалической коры

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

Southern Urals lamproites: the problems of terminology, age, and geodynamic interpretation

We have studied mineral and chemical composition of lamproites from Kalymbaevsky Complex the Middle Trias. These lamproites were developed in Magnitogorsk and Eastern-Urals megazones of the Southern Urals. We have established the presence of olivine, phlogopite, diopside phenocrysts. We have registered the presence of globular structures, consisting of sanidine and interstitial glass. We have also shown the presence in the base of rocks microlites of aluminous diopside-augite and alkaline pyroxenes of aegirin-augite series, which previously were taken for alkaline and sub-alkaline amphiboles. We have established high sulfur concentration in the apatite which, without magmatic sulfides in the rocks, witnesses for oxidation of lamproite magmas. For the first time precise geochemical data for microelemental and isotopic Sr, Nd composition of rocks are given. It was found that the South Urals rocks have a intermediate composition between lamproites and potassium alkaline basalts. Their source was the enriched mantle with the value εNdi = +0.7-+3.9. We have shown uncertainty of geochronological data, according to which lamproite magmatism could be initiated 197-240 or 300-310 Ma

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

ZIRCONS FROM ROCKS OF THE MURZINKA-ADUI METAMORPHIC COMPLEX: GEOCHEMISTRY, THERMOMETRY, POLYCHRONISM, AND GENETIC CONSEQUENCES

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

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