The study focuses on substantiating the hypothesis of the two-stage and two-level formation of the Darya Complex, which was proposed in the first article of the series. Isotopic and petrogeochemical studies of magmatic rocks from the Dar’ya Complex revealed that primary melts of alkaline ultrabasic and basic rocks are products of the deep mantle level, which formed under a peculiar fluid regime with the involvement of H2O and CO2 from a mantle source (Bulk Silicate Earth (BSE) or Primitive Mantle (PM type) variably and locally metasomatized and approaching the Enriched Mantle type I (EM-I) composition. Trace element and isotope systematics was found to be consistent with the hypothesis of the origin of ultrabasic and basic alkaline melts of the complex through the decompression melting of an enriched peridotite source in the asthenospheric mantle. REE modelling also suggests that the alkaline ultrabasic and basic rocks of the complex may have formed by partial melting of a carbonated garnet-bearing peridotite source. Isotopic and petrogeochemical characteristics of the magmatic rocks of the complex indicate that the evolution of each of the primary magmas was driven by the fractional crystallization and crustal contamination. The formation of alkaline mesites and salites is associated with the different-scale selective assimilation of crustal material by high-temperature, fluidized, basic mantle magmas during their ascent to the surface. Geological and compositional data on the Dar’ya svyatonosites demonstrate that melt hybridization with carbonate matter from the enclosing rocks of magma chambers played a critical role in their formation.

Geological data and petrogeochemical characteristics of the foidolite‒foidosyenite Dar’ya complex of the Ketkap‒Yuna magmatic province of the Aldan shield, together with the published isotope geochronological and geochemical data, suggest their formation in the Early Cretaceous in a setting of fundamental structural rearrangement of the southern periphery of the Siberian platform caused by the lithospheric plate sliding. The petrographic and petrogeochemical studies of magmatic rocks from the Dar’ya Complex showed that it was formed by the compositionally contrasting series: “kamafugite” and “tephrite-leucitite”−alkali-salic ones. The results of geodynamic discrimination of Dar’ya magmatic rocks indicate a continental-riftogenic (or close to it, in essence) origin of these rocks, which is consistent with one of the previously proposed interpretations of the geodynamic position for the formation of Late Mesozoic tectonic-magmatic activation zones of the Aldan Shield.

geological data, petrogeochemical characteristics of magmatites of the Kurung complex (the Ket-Kap-Yuna igneous province of the Aldan Shield), and previously published isotopic data along with the results of geochronology and geochemistry research provide evidence for this complex evolving in the Late Cretaceous in a setting of riftogenesis (final phase) of continental margins. Similar to the Late Jurassic-Early Cretaceous polyformational volcano-plutonism of the Aldan Shield, the Late Cretaceous alkaline magmatism in the Ket-Kap-Yuna province is associated with the tectonomagmatic activation which manifested itself mainly as continental margin rifting associated with deep reorganization of the southwestern, southern and southeastern framing of the Siberian craton triggered by gravitational sliding of the lithospheric plates. Results of the petrogeochemical analysis of the studied magmatites revealed that the heterogeneous rock groups identified within this rock complex are not related to each other by fractional or other type of differentiation, thus suggesting their possible derivation as a result of fluid syntexis-type interaction between mantle-derived alkali-basite melt and felsic crustal melts. Alkali-basite parent melts are shown to have formed during partial melting of variably enriched mantle which is widely spread beneath the Aldan Shield and is varied in composition (from BSE enriched to nearly EM-I). Origination of such deep-seated melts (magma sources) was associated with the rifting processes (strike-slip tectonics) triggered by the setting of gravitational sliding of lithospheric plates. The formation of alkaline-salic magmas of the Kurung complex is associated with large-scale selective assimilation of crustal material by high-temperature fluidized mantle magmas during their ascent to the surface, possibly as a result of fluid syntexis of alkaline-basite mantle magmas and crustal smeltings formed under their influence.

Геологические сведения и петрогеохимические характеристики магматитов курунгского комплекса Кеткапско-Юнской магматической провинции Алданского щита в совокупности с опубликованными ранее данными изотопной геохронологии и геохимии свидетельствуют о формировании его в позднем мелу в обстановке (завершающей фазы) окраинно-континентального рифтогенеза. Как и предшествующий ему позднеюрско-раннемеловой полиформационный вулканоплутонизм Алданского щита, позднемеловой щелочной магматизм Кеткапско-Юнской провинции связан с процессами тектономагматической активизации, которые проявились главным образом в виде окраинно-континентального рифтинга, сопряженного с коренной структурной перестройкой юго-западного, южного и юго-восточного обрамления Сибирской платформы, обусловленной обстановкой скольжения литосферных плит. Как вытекает из результатов петрогеохимического изучения магматитов комплекса, разноосновные группы пород в его пределах не связаны между собой отношениями фракционной или иного типа дифференциации, а являются, вероятно, производными флюидно-синтексического взаимодействия мантийного щелочно-базитового расплава и кислых коровых выплавок. Образование щелочно-базитовых материнских расплавов происходило при парциальном плавлении обогащенной в разной степени мантии, широко распространенной под Алданским щитом и варьирующей по составу от обогащенной BSE до близкой к EM-I. Зарождение столь глубинных областей плавления было связано с присдвиговым рифтингом, обусловленным существованием обстановки скольжения литосферных плит. Образование щелочно-салических магм курунгского комплекса увязывается с масштабным избирательным усвоением корового материала высокотемпературными флюидизированными мантийными магмами в процессе их подъема к поверхности, возможно, в результате флюидного синтексиса щелочно-базитовых мантийных магм и образовавшихся под их влиянием коровых выплавок. Integrated geological data, petrogeochemical characteristics of magmatites of the Kurung complex (the Ket-Kap–Yuna igneous province of the Aldan Shield), and previously published isotopic data along with the results of geochronology and geochemistry research provide evidence for this complex evolving in the Late Cretaceous in a setting of riftogenesis (final phase) of continental margins. Similar to the Late Jurassic–Early Cretaceous polyformational volcano-plutonism of the Aldan Shield, the Late Cretaceous alkaline magmatism in the Ket-Kap–Yuna province is associated with the tectonomagmatic activation which manifested itself mainly as continental margin rifting associated with deep reorganization of the southwestern, southern and southeastern framing of the Siberian craton triggered by gravitational sliding of the lithospheric plates. Results of the petrogeochemical analysis of the studied magmatites revealed that the heterogeneous rock groups identified within this rock complex are not related to each other by fractional or other type of differentiation, thus suggesting their possible derivation as a result of fluid syntexis-type interaction between mantle-derived alkali–basite melt and felsic crustal melts. Alkali–basite parent melts are shown to have formed during partial melting of variably enriched mantle which is widely spread beneath the Aldan Shield and is varied in composition (from BSE enriched to nearly EM-I). Origination of such deep-seated melts (magma sources) was associated with the rifting processes (strike-slip tectonics) triggered by the setting of gravitational sliding of lithospheric plates. The formation of alkaline–salic magmas of the Kurung complex is associated with large-scale selective assimilation of crustal material by high-temperature fluidized mantle magmas during their ascent to the surface, possibly as a result of fluid syntexis of alkaline–basite mantle magmas and crustal smeltings formed under their influence.

The first 40Ar/39Ar isotopic age data for hydrothermal vein gold mineralization in the late Mesozoic Ketkap-Yuna igneous province of the Aldan shield confirm the correlation between this style of mineralization and the Early Cretaceous sub-alkali magmatism, which was established by geological observations. The combination of geological characteristics and U-Pb data on magmatites enabled us to indirectly determine the age of the highly productive bimetasomatic «massif-skarn» type of mineralization associated with sub-alkali magmatogenic formations of the province. The isotopic dating of magmatites and gold mineralization in the Ketkap-Yuna igneous province and other late Mesozoic igneous provinces of the Aldan shield shows consistency in the ages of ore-bearing magmatites and associated ores. The delay in time of the Late Mesozoic magmatism manifestations in the Ketkap-Yuna igneous province and the associated gold mineralization relative to the intensification of tectonomagmatic processes in the Western and Central Aldan, as well as differences in the correlations of different types of igneous formations in the provinces, are explained by the characteristics of the regional tectonic structure and, as a consequence, the specific nature of the Late Mesozoic magmatism development in different parts of the Aldan shield. Two large areas of the late Mesozoic intensification of tectonomagmatic processes are identified in the Aldan shield that differ both in the time of the onset of polyformational magmatism and the accompanying different-type mineralization, and in the dominant formational type of magmatites: West-Central Aldan, on the one hand, and East Aldan, on the other. The former is characterized by continuous magmatic activity from the Berriasian to the early Albian (≈ 30 Ma) and predominance of the leucitite–alkali-(foid)-syenite formation, and the latter by manifestations of magmatism over a timeframe half of the above period (≈ 15 Ma) and predominance of the subalkaline diorite-granodiorite-granite formation. The termination of the late Mesozoic magmatism in both areas was subsynchronous. A «set» of magmatogenic formations in them is also similar: leucite-alkaline-(foid)-syenite with alkali granites, monzonite (shonkinite)-syenite and subalkaline diorite-granodiorite-granite. The Coniacian–Santonian outbreak of alkali volcano-plutonism during the intensification of tectonomagmatic processes is characteristic of the East Aldan region, which manifested itself in the Ketkap-Yuna igneous province after a long (about 30 Ma) period of amagmatism.

The first data of U/Pb and 40Ar/39Ar dating of volcanogenic rocks of the Pre-Dzhugdzhur volcano-tectonic trough (PDVT) of the Okhotsk–Chukotka volcanogenic belt (OChVB) confirm that the supra-subduction complexes, identical in composition and position in the geological section, were formed at different times in the main arc sector of the OChVB and adjacent flank zones. It has been established that the flank zones of the belt formed at different times as well. The main arc sector was formed with a lag of 9–11 Ma related to the Western Okhotsk flank zone and 5–8 Ma ahead related to the Eastern Chukotka flank zone. The results obtained have been analyzed along with the data on Albian magmatism of Northeastern Russia. This allowed us to suggest that the area of the future Pre-Dzhugdzhur and Ul’ya volcano-tectonic troughs was affected by active volcanism of the convergent margin regime during the Albian, when that part of the region that later became the main arc of the OChVB developed in the setting of the transformed margin.

ДИСКУССИИ ВВЕДЕНИЕКомментируемая статья [30] представляет несомненный интерес для петрологов-магматистов, палеовулканологов, геологов-съемщиков и тектонистов, занимающихся проблемами геологии, петрологии, геодинамики и палеовулканизма Северного Приохотья и Анадырско-Корякского региона России.В ней приведены новые аналитические данные по изотопной периодизации (K/Ar метод), неполные данные по петрогеохимии, краткие сведения по петрографии, результаты Nd-Sr изотопной систематики андезибазальтов и андезитов одного из разрезов так называемого гармандинского комплекса (в

Precision U–Pb (SHRIMP-II) isotope geochronological data, obtained for the first time, make it possible to suggest that sediments of the Neocomian primitive island arc sequence are missed or poorly developed in the South-Western part of the Mainitskii terrane of the Koryak Highlands. However, Late Albian mature island arc tuff and tuffaceous–turbidite formations are common. This enables us to extend the age range of the Mainitskii island arc from the Early Neocomian to the Late Albian and to suggest a two-stage pattern of its development. The isotope-geochronological data obtained for plagiogranite and moderately acid subvolcanics, previously attributed to the Koryak–Western Kamchatka volcanoplutonic belt, indicate that it is possible to combine them into the Middle Miocene postsubduction? polygenic complex. In addition, owing to modern high-precision isotope–geochronological methods, it has become possible to determine the age of gold–sulfide mineralization of the Talyaigin ore field, paragenetically related to the manifestations of the Middle Miocene Vilyuneiveem complex.

The Pb isotope composition of polyformational Mesozoic igneous rocks of the Ketkap–Yuna igneous province (KYIP) and lower crustal metamorphic rocks of the Batomga granite–greenstone area (the complex of the KYIP basement) of the Aldan Shield was studied for the first time. Based on the data obtained, several types of material sources participating in petrogenetic processes were distinguished. The mantle source identified as PREMA is registered in most of the igneous formations and predominates in mafic alkaline rocks. According to the isotope characteristics, the upper crustal source corresponds to a source of the “Orogen” type by the model of “plumbotectonics” or to the average composition of the continental crust by the Stacey–Kramers model. The lower crust is the third material source; however, the type of lower crustal protolith involved in the igneous process is still not defined, which makes difficult to estimate its role in the petrogenetic processes.

The protoliths of the Early Proterozoic metamorphic complex in the Batomga granite-greenstone terrane are proved to comprise two petrochemical series of volcanic rocks: calc-alkaline and komatiite-tholeiite. The metavolcanic rocks of the calc-alkaline series are metamorphosed basalts, andesites, dacites, and rhyolites. The topology of the trace-element patterns of the acid volcanics is similar to that of Archean gray gneisses in platform basements, and this suggests that the petrologic mechanisms that produced the protoliths could be similar. The metavolcanics of the komatiite-tholeiite series are determined to include komatiite and tholeiite basalts. Their chemical composition is consistent with the fractionation model of high-Mg basalts in intermediate chambers under low pressures. The Nb, Y, and Zr concentrations of the metatholeiites testify that their parental melts were derived from a plume source. The metamorphic culmination parameters of the rocks corresponded to the boundary between the amphibolite and granulite facies of elevated pressure.

В составе раннепротерозойского метаморфического комплекса Батомгской гранит-зеленокаменной области среди магматических протолитов выделены две петрохимические серии вулканитов: известково-щелочная и коматиит-толеитовая. Метавулканиты известково-щелочной серии представлены метабазальтами, метаандезитами, метадацитамии, метариолитами. Спектр распределения элементов-примесей в кислых метавулканитах имеет сходную топологию с архейскими серыми гнейсами фундамента платформ, что может свидетельствовать о близком петрологическом механизме формирования их протолитов. Среди метавулканитов коматиит-толеитовой серии выделены коматиитовые и толеитовые базальты. Их химизм согласуется с моделью фракционирования высокомагнезиальных базальтов в промежуточных камерах при низких давлениях. Содержание Nb, Y, Zr в метатолеитах свидетельствует о том, что их исходные расплавы имеют плюмовый источник. Кульминационные условия метаморфизма пород комплекса по температуре соответствуют граничной области амфиболитовой и гранулитовой фаций повышенных давлений.

Comparative U-Pb (zircon- and sphene-based, for the first time) and K-Ar (biotite-, amphibole, and whole rock-based) dating of monzonitoids and subalkaline granitoids of the Ket-Kap and Uchur volcanic-plutonic complexes (Ket-Kap-Yuna Igneous Province is one of the areas of tectonic-magmatic activation of the Aldan Shield), respectively, has been made. The new data, which are chiefly acquired by us for the first time, are close to each other and fall within the relatively narrow time interval of the mid-Early Cretaceous. The U-Pb sphene-based isochron datings indicate the formation time of the subalkali complexes at the Barremian-Aptian boundary. The values of SHRIMP age for zircons from the Uchur Complex subalkali diorites vary from 124.4 to 120.1 Ma; variations in U-Pb dates for monzonitoids of the Ket-Kap Complex fall in the narrower interval of 125.8–123.6 Ma. The extraordinary cases of highly polymodal distribution of SHRIMP-derived zircon-based dates are explained by the presence of detrital zircon crystals probably belonging to the protolith; this is interpreted by evidence for participation of the ancient continental crustal material in the formation of the source for the KKYuIP subalkali magmas. The range of the new K-Ar datings based on the whole rock composition of subalkali rocks and on the results of monomineral determinations is wider; however, it corresponds to the Early Cretaceous as well. This is significantly in contrast with the data given in the literature and geological survey reports. It was found for the first time that the duration of the subalkali magmatism manifestation in the KKYuIP is only several Ma and, according to the precise U-Pb dating, falls within the Aptian age of the Early Cretaceous epoch; this is sharply in contrast to the previously derived dates that referred to Early Jurassic-Cretaceous age of the magmatism. This time interval probably marks the main stage (relative quiet phase under strong compression) in the evolution of the setting of mutual sliding between the Siberian Craton and Amurian megablock, according to geodynamical reconstructions by A.I. Khanchuk and his colleagues.

Проведено U-Pb (по цирконам) и Ar-Ar (по биотитам) датирование кислых вулканогенных пород северных секторов Охотско-Чукотского вулканического пояса (ОЧВП): Центрально- и Восточно-Чукотского. Установлен факт временного разрыва между формированием аналогичных по вещественному составу и положению в разрезе ОЧВП комплексов окраинно-континентального (надсубдукционного) типа в этих секторах. Материалы по уран-свинцовой датировке пантеллерита подтвердили данные о раннепалеоценовом возрасте кислых щелочных пород окраинно-континентально-рифтогенной (постсубдукционной) формации. Вкупе с аргон-аргоновыми датировками субщелочных кислых пород этой формации и литературными данными, они свидетельствуют о маастрихт-палеоценовом возрасте этой стадии вулканизма, относящейся к Анадырско-Бристольскому поясу. По имеющимся и вновь полученным аргон-аргоновым и уран-свинцовым датировкам, возрастной диапазон становления Центрально-Чукотского сектора составляет около тридцати миллионов лет, а Восточно-Чукотского – более двадцати.