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We studied the regularities of distribution of siderophile elements, including platinum group elements (PGE), in rock and in sulfides from Archean (2814 ± 51 Ma) peridotites collected in a fragment of deformed dike within the Bug granulite complex, Ukrainian Shield. In comparison with the primitive mantle, the studied rocks are enriched in Rh, Pd, Ni, Fe, and Co, and are characterized by low concentrations of other PGE. Sulfides are represented by a high-temperature variety of pentlandite and a small amount of chalcopyrite, with an inhomogeneous PGE distribution in them. Pd/Ir ratio typical of superchondrite is revealed for rocks and some sulfides. It is supposed that enrichment in Pd was not resulted from fractionation, but was rather related to mantle metasomatism. Saturation of the melt with sulfides and liquation process were favored by contamination of harzburgite with the host gneissic enderbite and fractionation of olivine. Solid sulfide solutions formed from sulfide melts at temperatures close to the crystallization temperature of magnesium phlogopite from a silicate melt.

The Sr isotope characteristic of carbonate rocks in the Central Azov Group has been reported (0.70322–0.70352), the Nd model age of silicate sediments has been calculated (2.34–2.31 Ga), and the U–Pb age of trondhjemites (2052 ± 5 Ma) breaking through carbonates was determined. According to the data obtained, the marine sedimentary cover of the Azov block making up the Early Precambrian Sarmatia Continent was formed in the Early Paleoproterozoic 2.23–2.34 Ga ago.

Data on the U–Pb (SIMS SHRIMP-II) age (3628 ± 38 and 2845 ± 65 Ma) of zircon from the inclusion of mafic granulite in gneiss–enderbites of the Bug complex in Ukraine are obtained. A zircon age of 3628 ± 38 Ma for the first time has allowed us to identify the occurrence of basic magmatism at the Paleo- and Eoarchean boundary in the Bug region. The age of 2845 ± 65 Ma dates the imposed metamorphism manifested everywhere in the Bug region that led to considerable amphibolization and partial melting of the rock.

Актуальность исследования. Информация о составе, льдистости и геохимических особенностях мерзлых пород необходима при освоении нефтегазоконденсатных месторождений Ямала, Гыдана и Таймыра. Среди факторов, определяющих экологию тундровых ландшафтов криолитозоны, большое значение имеют подземные льды, в том числе полигонально-жильные, и последствия их вытаивания. Гидрохимический состав и содержание редкоземельных элементов в сингенетических жилах фиксируют информацию об источниках влаги и условиях, при которых происходило их формирование. Соотношение основных ионов и распределение редкоземельных элементов в растворе может быть использовано для оценки влияния на состав льда атмосферных осадков, морских и вулканических аэрозолей, антропогенного загрязнения. Цель: выявить источники поступления химических элементов и оценить влияние типа льдовыделения на гидрохимический состав и распределение редкоземельных элементов в различных генетических типах льда - полигонально-жильном, морском, озерном и фирновом льдах. Объекты: полигонально-жильный лед, вмещающие его отложения, сезонные льды, поверхностные воды, отобранные в экспедициях ИКЗ ТюмНЦ СО РАН в 2009-2014 гг. Методы исследования химического состава: масс-спектрометрия с индуктивно связанной плазмой, атомно-абсорбционная спектрометрия, эмиссионная фотометрия, хроматография. Результаты. Установлено, что на химический состав полигонально-жильных льдов, изученных в прибрежной зоне ключевых участков о. Белый, о. Сибирякова, Западного Ямала и Западного Таймыра, имели влияние морские и континентальные аэрозоли. Сингенетические полигонально-жильные льды, пресные и ультрапресные по минерализации, сформированы при промерзании талых вод, которые содержат сорбированные снегом морские аэрозоли - взвешенные в атмосфере твердые и жидкие частицы. Полигонально-жильные льды в удаленном от моря районе оз. Сохонто не имеют признаков морского влияния по соотношению основных ионов. Полигонально-жильные льды с минеральными включениями формировались не только за счет талых снеговых вод с аэрозолями континентального происхождения, но и за счет надмерзлотных вод. В полигонально-жильных льдах выявлено увеличение содержаний лантаноидов в водорастворимой форме по сравнению с кларковыми значениями и современными поверхностными льдами. По цериевой аномалии в большинстве изученных сингенетических ледяных жил подтверждается участие морских аэрозолей. По распределениям редкоземельных элементов выявлено характерное для полигонально-жильных льдов соотношение легких и тяжелых редкоземельных элементов равное 0,9, и соотношение лантана к остальным лантаноидам, равное 0,2. Морской лед наследует минерализацию и состав морской воды. Озерный лед различается по глубине и отражает сезонное изменение гидрохимического состава при ледоставе и повышение концентрации морских аэрозолей в снеге, перекрывающем озерный лед. Фирновый лед полярного Урала имеет очень низкую минерализацию, в нем отсутствуют примеси морского аэрозоля. В полигонально-жильных льдах голоценового и неоплейстоценового возраста реализован природный механизм накопления редкоземельных элементов в водорастворимой форме в комплексе с железом, торием и иттрием. Вытаивание ледяных жил может приводить к поступлению редкоземельных элементов в поверхностные воды. Relevance of the research. Information on composition, ice content and geochemical characteristics of frozen rocks is necessary for exploration of oil and gas condensate fields of Yamal, Gydan and Taimyr. Among the factors determining the tundra landscapes ecology of the cryolithozone, underground ice and their melting have great importance. The hydrochemical composition and rare-earth elements content in syngenetic ice wedge retain the information on the moisture sources and conditions of their formation. The main ions correlation and rare-earth elements distribution in the ice composition can be used to estimate the influence of such natural factors as precipitation, sea and volcanic aerosols and anthropogenic pollution. The main aim of the research is to identify chemical elements sources and to assess the impact of the ice type on hydrochemical composition and rare-earth elements distribution in different genetic types of ice - wedge, seasonal and firn ice. Objects: ice wedge, sediments rocks, seasonal ice, surface water, taken in expeditions Earth Cryosphere Institute, Tyumen scientific centre SB RAS in 2009-2014. Methods of chemical research: inductively coupled plasma mass spectrometry, atomic absorption spectrometry, emission photometry, chromatography. Results. It is established that marine and continental aerosols influenced the chemical composition of ice wedge studied in the coastal zone of the key areas of Belyj island, Sibiryakova island, Western Yamal and Western Taimyr. Fresh and ultrafresh syngenetic ice wedge is formed by freezing melt water, which contains snow-sorbed sea aerosols - suspended in the atmosphere solid and liquid particles. Ice wedge in the lake Sokhonto area long-distanced from the sea has no signs of marine influence according to the main ions content. Ice wedge with mineral inclusions was formed not only due to snow melt water with aerosols of continental origin, but also due to the suprapermafrost water. It was found out that lanthanide content in water-soluble form has increased in comparison with both сlark values and the content in the modern surface ice. In the most of examined syngenetic ice wedge the participation of marine aerosols is confirmed taking into account the cerium anomaly. Moreover according to the distribution of rare-earth elements the correlation between light and heavy rare-earth elements typical for ice wedge, equal to 0,9, and correlation between lanthanum and the other lanthanides, equal to 0,2, are observed. Sea ice inherits the mineralization and composition of sea water. Lake ice varies in depth and reflects seasonal changes in hydrochemical composition of ice and increases in concentration of marine aerosols in the snow covering the lake ice. Firn ice of the polar Urals has a very low mineralization, there are no impurities of sea aerosol. The natural mechanism of rare earth elements accumulation in water-soluble form in combination with iron, thorium and yttrium is implemented in ice wedge of the Holocene and Neopleistocene. Melting out ice wedge may lead to the flow of rare-earth elements in the surface water.

Complex study of the U–Pb and Lu–Hf systems of zircon from a lhertzolite lens of Archean gneiss enderbites of the Bug complex, Ukrainian Shield, showed that ultramafic magma was contaminated by the material of the country gneiss enderbites. The age of the zircons of 2.81 ± 0.05 Ga corresponds to the period of ultramafic magmatism within the Bug complex. Previously, this peak of endogenic activity was considered the stage of manifestation of metamorphism and magmatism of mafic composition.

Based on our new U–Pb isotope data (SHRIMP-II) for the Voronezh Crystalline Massif (VCM) and on published U–Pb data for the Archean rocks of the Ukrainian Shield (USh), we have substantiated the main stages of the Archean evolution of the Sarmatian crust, a fragment of the basement of the East European Platform. New data have been obtained for 20 indicative rocks of the Kursk block (KB) of the VCM. We compared the Eoarchean and Paleoarchean KB rocks (mafic rocks and tonalites of the Oboyan’ complex), orthogneisses of the USh Dniester–Bug province (Bug granulite complex), and tonalites and mafic rocks of the USh Azov Province and have established the existence of ancient continental crust (3.75–3.60 Ga) in Sarmatia. The presence of Paleoarchean xenogenic zircons in younger intrusions indicates a wide spread of Paleoarchean rocks in the deep VCM crust section. In the Mesoarchean (3.2–3.0 Ga), eastern Sarmatia (KB and Azov and Middle Dnieper provinces) was a single granite–greenstone terrain. Two stages of felsic magmatic activity have been dated: 3.15–3.10 Ga (volcanics in the greenstone belts and tonalite–trondhjemite granites in the VCM and USh) and 3.05–3.00 Ga (volcanics and tonalite–trondhjemite granites in the USh and granites in the VCM KB). Magmatic and tectono-metamorphic processes (2.95–2.85 Ga) have been established throughout the eastern part of Sarmatia. The latest Mesoarchean endogenic activity (2.85–2.80 Ga) testifies to the tectonic differentiation of the area. Mafic and felsic magmatism, deformations, metamorphism, and ultrametamorphism under amphibolite and granulite facies conditions took place in the most part of the KB and in the Azov and Bug areas. It is shown that ultrametamorphic granites formed from an ancient (3.0–3.5 Ga) protolith. The USh Middle Dnieper province had a different tectonic position. Here, intrusion of post-tectonic granites and formation of mature sediments proceeded at 2.81–2.86 Ga. Our geochronological data show that most of the Sarmatian continental crust formed in the Mesoarchean as a result of both the intrusion of juvenile material and the reworking of the older protolith rocks. Neoarchean events (2.8–2.5 Ga) are weakly expressed in Sarmatia in contrast to Baltia, another large fragment of the East European Platform basement, where endogenic processes at 2.65–2.75 Ga were the major crust-forming geologic events.

This paper presents the results of a complex study (morphology of grains, internal texture in cathodoluminescence and backscattered electrons, microprobe analysis, Lu–Hf data) of five groups (generations) of zircon crystals differing in age and separated from the same granulite sample pertaining to the Bug River Complex of the Ukrainian Shield. The data show that the oldest zircon crystals of the first group (3.74 Ga in age) are xenogenic and initially crystallized from a granitic melt; zircon of the second group (3.66 Ga) formed from a mafic melt contaminated by felsic country rocks. The third group (3.59 Ga) is represented by zircons that formed about 100 Ma later than the second group under conditions of granulite-facies metamorphism and with the participation of fluid-saturated anatectic melt. Two Paleoproterozoic zircon groups (~2.5 and 2.1 Ga) also formed under granulite-facies conditions; to a certain extent, their structure and composition were controlled by fluid. The geochemistry of all zircon generations provides evidence for their crystallization in the continental crust, but from the sources differing in the contribution of mantle-derived material and in oxygen fugacity.

Garnet-bearing aluminous gneisses in the Vasil’kovka area of the Orekhov–Pavlograd zone of the Ukrainian Shield were studied using the THERIAK-DOMINO, THERMOCALC, and WINTWQ software and mineral geothermobarometry methods. The stability fields of parageneses formed at the initial, peak, and post-peak metamorphic stages have been estimated: T = 500–650 °C and P > 7 kbar, T = 800–850 °C and P ≈ 8 kbar, and T = 600–670 °C and P = 4.0–5.5 kbar, respectively. A “clockwise” PT path has been established. Based on the aluminous gneiss, the age of metamorphism is determined as Paleoproterozoic (2014 ± 11 Ma). Unique regularly oriented acicular goethite microinclusions were described in garnet. In contrast to other known oriented Ti-bearing mineral inclusions in garnet, these goethite inclusions suggest not only extremely high P and T values (necessary for the formation of oriented Ti-bearing inclusions) but also a high oxygen fugacity. The obtained data broaden the concepts of the ways and conditions of formation of regularly oriented mineral phases in garnet.

This report presents data on the geological structure and location of the orthopyroxenite inclusion in gneissic enderbites of the Bug granulite–gneiss domain. Three stages of orthopyroxenite formation were identified on the basis of studies of the mineral composition along with the U–Pb and Lu–Hf isotope systems of zircons.

We performed a joint analysis of SHRIMP II U-Pb ages (68 measurements for 5 rock types) and trace and rare-earth element compositions of zircons (41 determinations made in the same points that were utilized for measurement of U-Pb isotope ratios) from the complex Orekhovo-Pavlograd shear zone of the Ukrainian Shield. It was determined that this zone is composed of rocks of different age: 3.5, 3.4, 2.8, and 2.0 Ga. The main stage of structural-metamorphic reworking took place 2.0 Ga and lasted for over 30 Ma. It was established that fluid reworking of zircons was accompanied by an increase of LREE content and decrease of Ce anomaly. The preservation of U-Pb system in some zircons with high LREE contents may be explained by their solid state transformation.

The available geological, petrological, and isotopic data on Archean rocks of the Baltic shield are used to analyze the formation of the crust of the ancient Vodlozero domain. This made it possible to reveal the succession of endogenic processes in different parts of the domain and correlate them between each other. Several stages of magmatic processes reflecting changes in magma-generation environments are definable in the crust formation. The earliest stages of magmatism (3.24 and 3.13–3.15 Ga) are mostly represented by rocks of the tonalite-trondhjemite-granodiorite association. The next stage of endogenic activity (3020–2900 Ma) was marked by the formation of volcanics of the komatiite-basalt and andesite-dacite associations constituting greenstone belts in marginal parts of the Vodlozero domain and basic dikes accompanied by layered pyroxenite-norite-diorite intrusion in its central part. These basic bodies crossing earlier tonalities were formed in extension settings related to the formation of the mantle plume, which is confirmed by the rock composition. This stage culminated in the formation of trondhjemites at margins of greenstone structure. The next stage of endogenic activity commenced at 2890-2840 Ma by the emplacement of high-magnesian gabbro and diorite dikes in the western margin of the domain, where they cross rocks of the tonalitetrondhjemite association. This stage was marked by the formation of intermediate-acid subvolcanic bodies and dikes as well as basite intrusions including the layered and differentiated Semch intrusion, the largest one in the Vodlozero domain. The stage culminated at approximately 2850 Ma in the emplacement of tonalities of the limited distribution being represented by the Shilos massif in the north of the domain and Shal’skii massif on the eastern shore of Lake Onega. The important stage in the geological history of the Vodlozero domain is the formation of the intracratonic Matkalakhta greenstone belt at approximately 2.8 Ga, which includes arenite quartzite and graywackes and polymictic conglomerates developed in the Lake Oster area in addition to volcanics. These rocks indicate a stable tectonic regime, which resulted in deep erosion of the crust. The emplacement of sanukitoids (2.73–2.74 Ga) as well as subsequent two-feldspar granites (2.68–2.70 Ga) and basite dikes (2.61–2.65 Ga) may be considered as resulting from the plume influence on the relatively stabilized sialic crust of the Baltic shield.

The Orekhov–Pavlograd Zone (OPZ), which is located in the Ukrainian Shield, represents the reworked western margin of the Archaean Azov Province and separates it from the Archaean Middle Dnieper Province. In the Vasilkovka area, which is located in the northern OPZ, Archaean tonalites and amphibolites and Palaeoproterozoic quartzites, high-Al paragneisses, and mafic granulites were studied. Structural observations allow the OPZ to be interpreted as a steep transpressional ductile shear zone. The tonalites and amphibolites were dated at 3.50 and 2.88 Ga, respectively (SIMS zircon ages hereafter). The metasedimentary rocks originated from mature sediments from Archaean continental sources and were deposited in a shallow intracratonic basin. The basaltic protoliths of the mafic granulites were produced by a mantle-plume-related source in a quiescent intraplate setting. Several metamorphic events were recognised (3.5, 3.4, 3.3, 2.85 and 2.1–2.0 Ga). The main metamorphic reworking occurred in the Palaeoproterozoic; its onset was dated at 2.08–2.07 Ga, and it ended at 2.00–2.01 Ga. The earliest Palaeoproterozoic metamorphism occurred at P = ca . 8.5 kbar and T = ca . 600 °C, then at P = 5–7 kbar and the peak metamorphic temperature T = 830 °C, and the final stage was at T = ca . 600 °C and P = 3.3–4 kbar (based on the TWEEQU and THERIAK-DOMINO methods), which suggests a clockwise P–T–t loop. In small shear zones, the Archaean tonalites were converted to garnet–biotite gneisses that inherited the tonalitic geochemistry and Palaeoarchaean magmatic zircons. Subduction-related igneous rocks and accretionary prism sediments are absent in both the Vasilkovka area and the entire AP, which makes subduction-related models questionable. An alternative tectonic model for the OPZ could be an intracratonic (intraplate) ductile shear zone that developed due to far-field stresses due to the tectonic juxtaposition of the Sarmatia and Volgo-Uralia continental blocks, which were parts of the East European Craton. Regional metamorphism and the coeval emplacement of mantle-derived igneous rocks and crust-derived granites are suggested to have been produced by magmatic underplating at ca . 2.02–2.10 Ga. This model needs to be developed further.

Paleoarchean granulite-facies metasedimentary rocks (quartzites, garnet quartzites, garnet-pyroxene gneisses, pyroxene-magnetite and magnetite quartzites) attributed to the Dniester-Bug Group of the Ukrainian Shield were studied. On the basis of geochemical data, including REE, the primary composition of these rocks was reconstructed as association of Fe-rich sandstones and sublitharenites, Fe-shales, and BIFs. This sedimentary association is similar to the rocks of other ancient greenstone belts and ascribed to the Algama-type iron formation. The sum of Al2O3, CaO, Na2O, and TiO2, high Zr contents (>100 ppm in quartzites), and the presence of detrital zircon grains of different ages are consistent with the terrigenous nature of sedimentary rocks. The Sm/Nd, Ti/Zr, Sc/Zr, and Ni/Zr ratios indicate the predominance of granitoid rocks in the source areas. The elevated Cr contents suggest that, in addition to granitoids, the source area contained ultramafic rocks. Geochemical characteristics, such as Fe/Mn ratio, low REE contents, and variations of REE versus the sum of Ni, Co, and Cu testify that sedimentation occurred under shallow-water conditions on the continent or its slope, similarly as the formation of ancient (3.5–3.2 Ga) basalt-komatiitic series intercalated with sedimentary rocks in the Pilbara Craton. The age of supracrustal rocks of the Dniester-Bug Group was constrained within the time interval of 3.4–3.2 Ga on the basis of U-Pb zircon dating and determination of Nd isotope composition. The DM model age of quartzites varies from 3.37 to 3.5 Ga. Sedimentary rocks together with volcanic rocks represent the oldest supracrustal association of the East European Platform.

The SIMS U-Pb isotopic age of zircons from enderbite gneisses and their metaorthopyroxenite xenoliths in the Pobuzhie granulite complex, Ukrainian Shield (48°13′57.3″ N and 29°59′21.5″ E, WGS84 system), was determined. The chemical compositions of these rocks and composing minerals were studied. Enderbite gneisses contain quartz, antiperthite plagioclase, K-feldspar, clinoenstatite, diopside, amphibole, and a small amount of biotite; accessory minerals are ilmenite and apatite. The age of zircon from enderbite gneiss is estimated at about 3.15 Ga. Metaorthopyroxenites are composed of orthopyroxene, clinopyroxene, phlogopite (up to 6% TiO2), and plagioclase. The age of magmatic zircons from metaorthopyroxenite determined by the upper intercept of the discordia with the concordia is 3485 ± 33 Ma (MSVD = 1.6), and the age of metamorphic zircons is 2742 ± 22 Ma (MSVD = 0.22). Hence, the enderbite gneisses studied pertain to a young group of enderbites in the Pobuzhie granulite complex, while the age of metaorthopyroxenites from xenoliths in these rocks is similar to that of ancient Pobuzhie enderbites and pyroxenites of the Novopavlovsk complex in the Azov Region.

The geological setting, geochemistry, and Nd isotopic systematics of tonalite-trondhjemite-granodiortite (TTG) series in ancient cratons are considered. It is shown that the TTG series were formed from ∼4.2 to 2.6 Ga ago in the oldest continental cores; many TTG series do not reveal chronological links to greenstone belts. This follows from the evolution of the Slave Craton in the Canadian Shield, the Vodlozero Craton in the Baltic Shield, and the Pilbara and Yilgarn cratons in the Australian Shield, where greenstone associations postdated TTG series. As has been established at the Baltic Shield, the primary melts of the Mesoarchean TTG associations were formed at a shallower depth (P 150 Ma) that separates the formation of the TTG melts from the age of the source involved in melting. Taking into account the calculated rate of cooling of the lithospheric plates, these data indicate that most Archean TTG series likely were not formed in the convergent subduction-related and accretionary geodynamic settings. The isotopic and geochemical data constrain compositions of the sources that produced Archean TTG series. Petrologic modeling of the formation conditions and Nd isotopic composition of the metabasalts in greenstone belts show that these rocks could not have been the source of TTG series. The most plausible isotopic and geochemical analogue of this source are the Archean amphibolites (ENd mafic rocks), which differ from the metabasalts of greenstone belts by their lower Sm/Nd ratio and enrichment in some lithophile elements. The available data suggest that the primary TTG melts were generated as products of melting of amphibolites and granulites forming the lower crust.

The novel detailed geological and geochronological data for the tonalitie rocks and products of its structural and metamorphic overprint in the Orekhovo-Pavlogradskaya collision zone (Ukrainian Shield) are discussed. Magmatic crystallization of tonalites (3500 ± 13 Ma) followed by amphibolite (2863 ± 22 Ma) and granulite (2105 ± 40 Ma) facies metamorphic events, resulting in biotite-garnet gneisses formation. The last date also indicating the time of collision event. The earliest age of 3.64 Ga was found in the zonal zircon fragment within 3.5-Ga old magmatic zircon from tonalite.

This work considers geochemical and isotopic characteristics of the source of the Archean Panozero pluton derived from LILEand LREE-enriched lithospheric mantle. Sr and Nd isotopic data on clinopyroxenes and augites define a source with Sri = 0.7017 and ɛNd(t) varying within a narrow range from + 0.7 to + 1.4 (averaging + 1.1), which is close to previously obtained whole-rock isotopic data. Similar ɛNd(t) were obtained for the Archean alkaline rocks of Canada, whereas the Archean mafic rocks of the Baltic and Canadian Shields formed from depleted mantle have ɛNd(t) ∼2. Lead isotope measurements on K-feldspars (KFsp) and monzonite showed that the source of the pluton has μ = 8.98 for the Stacey-Kramers two-stage model, at low U/Pb and high Th/U ratios. Different lead isotope composition corresponding to μ = 10.43 was determined in KFsp from quartz monzonites. Diverse interpretations of obtained data have been proposed. It was noted that the Pb-Pb isotopic system was disturbed by a later (∼ 1.9 Ga) thermal event. The ratios of elements of similar compatibility were used to determine the geochemical specifics of source of the Panozero pluton. Their comparison with numerous literature data on metasomatized mantle xenoliths and minerals in them showed that the mantle source strongly differed from primitive mantle in ratios of elements, whose mineralmelt partitioning coefficients considerably differs from mineral-fluid partitioning, for instance, Nb/La. Mantle source that was responsible for geochemical peculiarities of the Panozero pluton was made up of Phl, CPx, and Ap.

This work addresses the isotopic heterogeneity of the Archean lithospheric mantle by the example of high-Mg, moderate-alkali, LILE and LREE-enriched Panozero sanukitoid massif, which is located in the Central Karelia, southeastern Baltic Shield. Initial Nd and Sr isotope characteristics were determined for mantle source of the massif. ɛNd(T) in the source are plotted below DM line, varying from + 0.7 to + 1.4 (+1.1, on average). The 87Sr/86Sr(T) ∼ 0.7017 significantly exceeds that of depleted mantle and reflects change of Rb/Sr ratio in the source due to metasomatic reworking of mantle. Data on Pb isotope composition of potassium feldspars indicate that source of monzonites of the Panozero Massif had lower μ (238U/204Pb) = 8 and higher (238Th/232U) = 4.05 relative to primitive mantle.

Ion microprobe study of rare-earth and trace element composition of zircons from miaskite lamproites of the Panozero sanukitoid complex in Central Karelia made it possible to divide them into weakly altered and metasomatically altered zircons. The latter differ in elevated contents of LREE, Ca, Al, Fe, Ti, Sr, Ba, and Th, a flat REE distribution pattern, and a reduced Ce anomaly. Zircons show moderate to strong degrees of alteration, which are recorded in their geochemical features. The metasomatic alteration was caused by fluid related to the mantle alkaline magmatism. At the final stage, this fluid caused the crystallization of zircon domain with extremely high contents of REE (55000 ppm), Ti, Ba, Sr, and Th. The use of a Ti thermometer for unaltered zircons from the miaskite lamproites yields strongly underestimated temperatures, which require additional explanation or revision of the thermometer. For strongly altered zircons with sharply elevated Ti content, the use of this thermometer seems to be impossible.

The structure and composition of accessory zircons from the tonalites of the Vyg River, southeastern Karelia, were investigated. Their local U-Pb SHRIMP dating yielded ages between 3127±15 and 3146±25 Ma. It was shown that the zircons consist of three zones, a central part containing solid and melt inclusions and zoned magmatic and metasomatic shells. The obtained ages correspond to the magmatic and metasomatic stages of zircon crystallization. In general, the zircons have elevated contents of LREE (up to 867 ppm La), which were mainly accumulated in the outer metasomatic shell. Apatite and CO2 inclusions are widespread. Orthoclase, orthopyroxene, ilmenite, galena, quartz, and bastnaesite were identified in a solid inclusion in one zircon core using a CAMSCAN MX 2500 electron microscope. The presence of bastnaesite accentuates the relation of LREE with a CO2-rich fluid. It was shown that REE content is not correlated with U, Th, and U/Th ratio.

Geochemical, isotopic-geochemical, and geochronological information was obtained on magmatic rocks from the Saltychan anticlinorium in the Azov domain of the Ukrainian Shield. The rocks affiliate with the calc-alkaline series and a high-Mg series. The rocks of these series notably differ in concentrations of trace elements and REE and range from gabbro to granodiorite-quartz diorite in composition. The NORDSIM ionprobe U-Pb zircons ages of rocks belonging to the Obitochnen Complex and having both elevated and normal mg# correspond to 2908–2940 Ma. The Osipenkovskaya intrusion has an age of 2855 ± 19 Ma. The most alkaline North Obitochnen intrusion was emplaced in the Proterozoic, at 2074 ± 11 Ma. The age of the amphibolite metamorphism of the host gneisses is reliably dated at 3120–3000 Ma. The model Sm-Nd ages of the intrusive rocks do not exceed 3150 Ma. According to geochemical evidence, the parental melts of the magmatic rocks were derived from mantle domains variably enriched in lithophile elements. The results obtained by studying the Sm-Nd isotopic system corroborate the conclusion drawn from geochemical evidence that most of the melts were derived from the mildly enriched mantle, practically without involvement of ancient crustal material. The mantle became enriched in LREE at approximately 3000 Ma, which corresponds to the age of metamorphism of the supracrustal rocks. This process was separated from the derivation of the melts by a time span of 70–80 Ma. The relative age of the intrusive rocks and their variable composition can be most adequately explained by a contribution of heat and material from a plume to the derivation of the parental melts of these rocks.

The high-K and high-Mg Panozero central-type intrusion is located on the shore of Lake Segozero, Central Karelia, and has an age of 2737 ± 10 Ma. Detailed mapping and petrological study showed that it was formed in three magmatic cycles that were separated by lamprophyre dikes. The first cycle is composed mainly of mafic rocks (layered complex: pyroxenites-honblendites-monzogabbro) and monzonites 1; the second cycle includes monzonites 2, and the third cycle comprises monzonites 3 and quartz monzonites. The massif is cut by numerous lamprophyre dikes and breccia zones. As compared to calc-alkaline series, the studied rocks are enriched in K, Ba, Sr, P, LREE, have high mg# (mg# = 0.5–0.65), and elevated contents of Cr and Ni. The parent composition of the layered complex was determined to be monzogabbro. Model calculations showed that the compositional variations of the Panozero Complex are consistent with the fractional crystallization of monzogabbro. The melts were fractionated in an intermediate chamber and during the flowing and crystallization of the magma. The parent melt of the intrusion was formed by the partial melting of mantle enriched in some LILE, LREE, and volatiles (CO2 and H2O). The volatile enrichment of the melt manifests itself in the mineral composition of the rocks, the presence of primary gas inclusions in apatite, and diverse structural features. The comparison of the rocks of the Panozero Massif with metasomatized mantle xenoliths in the variation diagrams for incompatible elements showed that the mantle source of the Panozero Complex was metasomatized by fluid consisting of H2O and CO2 of different origin.

A simple, reliable, and high-performance method has been proposed for direct determination of the isotopic composition of authigenic uranium in silica lacustrine sediments. The method is based on studying the kinetics of the selective extraction of authigenic uranium from sediments with weak solutions of ammonium hydrocarbonate followed by the ICP-MS analysis of the nuclides. To estimate the contamination of authigenic uranium by terrigenous one, the contents of 232Th and some other clastogenic elements in the extracts were measured simultaneously. The selectivity of extraction of authigenic uranium from the sediments treated with a 1% NH4HCO3 solution appeared to be no worse than 99%. The method was used to analyze the isotopic composition of authigenic uranium at several key horizons of a core dated before. The measurements directly prove that the 234U/238U values in Baikal water varied depending on climate, which contradicts the previous statements. The measured 234U/238U ratios in paleo-Baikal water match the values reconstructed from isotopic data for total uranium in the sediments on the supposition that the U/Th ratio is constant in the terrigenous part of the sediment. Direct experimental determination of total and authigenic nuclides in sediments enhances the potentiality of the method for absolute 234U-230Th dating of carbonate-barren lacustrine sediments, including those from Lake Baikal, within the intervals corresponding to the periods of glaciation, where the sediments contain a large fraction of terrigenous component. Given the fractions of terrigenous and authigenic uranium are accurately determined, we have an opportunity to study the variability of the sources of terrigenous matter and to refine the previous model for reconstructing the climate humidity in East Siberia.

Archaean supracrustal complexes, known in the Fennoscandian (Baltic) Shield, are described and discussed by analysing the time sections 3.1-2.9, 2.9-2.75 and 2.75-2.65 Ga. Data on granitoid complexes, interrelated in time and space, and evidence for Archaean metamorphic events are classified and presented briefly. Fragments of ophiolitic and eclogitic associations have been found in Archaean rocks in the Shield. The first evidence of continental crust in the Shield is from Meso-Archaean time (3.5-3.1 Ga); isolated microcontinents, such as Vodlozero, lisalmi and North Finland, have been identified. New continental crust was mainly generated in the 2.9-2.65 Ga interval. The geodynamic settings in which the continental crust was formed in the Meso-and Neoarchaean included subduction (ensialic and ensimatic), accretion and collisional mechanisms. The continental and oceanic crust were affected by mantle plumes.

Archaean high-Mg granitoids (sanukitoids) occur in the Karelian granite–greenstone terrain in the Baltic Shield in two distinct zones. In the west of the Shield sanukitoid intrusions formed between 2700 and 2720 Ma and consist of a single igneous phase that varies in composition from diorite to granite. In the Eastern part of the Shield, sanukitoid intrusions formed between 2730 and 2745 Ma and are strongly differentiated, varying in composition from ultramafic to felsic. All the sanukitoids are enriched in light rare earth elements (LREE: La≤80 ppm, Ce≤150 ppm, La N /Yb N ≤30–40), Sr≤2000 ppm, Ba≤2500 ppm, P 2 O 5 ≤1.5%, alkalis (Na 2 O+K 2 O=5–10%), possess high mg# values (0.50–0.65), and show a negative Nb–Ta anomaly. They are spatially and temporally related to syenite intrusions and lamprophyre dykes. Sanukitoid intrusions in the Western and Eastern zones differ in composition. In the west, they have higher SiO 2 (mainly>60%) and lower alkalis, Sr, Ba, LREE than in the Eastern zone intrusions. The most differentiated intrusion, the Panozero intrusion in the Eastern zone, was formed in two magmatic cycles separated by ductile deformation. In the first cycle, ultramafic to monzonitic rocks formed, whereas, in the second cycle, the magmas were monzodioritic to quartz monzonite. Ultramafic and mafic rocks make up about 10% of the outcrop and occur as enclaves in monzonites and monzodiorites, and, as dykes, implies a number of discrete magmatic events. All rocks of the Panozero intrusion have high K 2 O, and the composition of the initial melt, calculated from the weighted average of the first cycle magmas is monzodiorite (SiO 2 =52%, mg#=0.55, Na 2 O+K 2 O∼6%). The presence of magmatic hornblende and biotite, a high carbonate content, widely distributed explosive breccias and evidence of liquid immiscibility are consistent with a high H 2 O–CO 2 content in the sanukitoid melt. The geodynamic model which most satisfactorily explains our geological and geochemical observations is the formation of the Karelian sanukitoids in a cratonic environment adjacent to the Belomorian–Karelian suture.

The analysis of radiometric ages of Early Precambrian basites of the Fennoscan- dian shield, from the most ancient ones, >3.1 Ga, to 2.40 Ga, resolves five age groups of the basites. Each of these stages is shown to time span interval of 70-80 m.y. The early stages of the high-T mafic magmatism (>3.1 and 2.99-2.91 Ga) are confined to within the oldest core of continental crust in the Fennoscandian shield - the Vodlozero domain with crustal age of 3.2-3.4 Ga. The next stage of mafic magmatism (2.88-2.80 Ga) occurred within the Kola and western Karelian domains with crustal ages of 3.0 and 3.1 Ga and on the north of the younger, central Karelian domain. The last of the Archean stages of high-temperature mafic magmatism with ages of 2.72-2.66 Ga occurs in the north Karelian belts, in the Karelian part of the Belomorian area (the regions of Lake Notozero and the Tupaya Guba Bay of Lake Kovdozero) and possibly, in the western Karelian domain. This magmatism took place also immediately after the subduction processes at the boundary of the Karelian and Belomorian domains. The Early Proterozoic high-T mafic magmatism at 2.50-2.41 Ga was both the most areally extensive and continuos such episode in the Fennoscandian shield. Nearly all the researchers of the high-T basites of this stage attribute this magmatism to the ascent of a deep mantle super-plume. Paleomagnetic data provide further evidence that at 2.5-2.41 Ga a long-lived heat source occupied virtually the entire area of the present day Fennoscandian shield.

Our study of magmatic rocks provides grounds for discussing the successive phases and geodynamic conditions of continental crust generation between 3.2-2.83 Ga within the Fennoscandian shield. Three tectono-magmatic phases, 3.2-3.1 Ga, 3.0-2.92 Ga, and 2.92-2.83 Ga, are established. During the 3.2-3.1 Ga phase, voluminous intrusives were emplaced, creating the large Vodlozero "sialic core." Positive "Nd(t) values for mafites and, partly, granitoids point to a weighty contribution of juvenile material derived from a depleted mantle. At the same time, Nd isotope composition for a number of granitoid massifs and zircon ages suggest the presence of an earlier (as old as 3.5 Ga) crustal component. Endogenic processes that occurred during the second, 3.0-2.92 Ga phase, have been recorded in southeastern and western Karelia and are inferred to have occurred in the Kola Peninsula as well. During this phase, oceanic plateaus and island arcs were formed near, to be accreted onto, the western and eastern margins of the ancient Vodlozero core. Simultaneously, the central part of the Vodlozero "sialic core" was the locus of emplacement of gabbronorite-diorite intrusions and purely dioritic bodies, as well as vigorous tonalite- granodiorite magmatism, to form the Vodlozero domain, the oldest on the shield. In the western Karelian domain, rocks younger than 2.92 Ga are exposed at the current erosional surface. The presence of ancient material in western Karelian crust is pinpointed by Nd model ages for granitoids and volcanites and by a detrital zircon age from granite. The third, 2.92-2.83 Ga phase entailed further reworking of ancient terranes and initiation of new sialic cores. At the northern margin of the Vodlozero domain and within the western Karelian one, a system of rift-related features came into being, eventually to evolve into bimodal greenstone belts largely dominated by mafic and ultramafic volcanites. The Kola province provided the stage for inception of rift-related greenstone belts with their associated komatiite-tholeiite (2.92-2.87 Ga) series followed by the basalt-andesite-dacite (2.88-2.79 Ga) series. Apparently, these belts in their present-day form, just like those of the western and eastern margins of the Vodlozero domain, result from tectonic juxtaposition of rock assemblages that originated from a variety of geodynamic settings. Archean continental crust of the Fennoscandian shield is shown to have formed through both progressive addition of sialic crust over time, mainly at convergent boundaries of ancient plates, and via reworking of ancient fragments, which involved input of juvenile material resulting from rising mantle plumes. In all likelihood, ascending mantle plumes are responsible for the formation of accretionary and collisional orogens, whereas the coeval magmatism at active plate margins was due to subduction (in the context of the plate tectonic mechanism). Generation of rift-related structures and associated magmatism may have been driven by rising mantle plumes. Brittle deformations leading to rifting and associated with the ascent of mantle plumes did not result in break-up of the young continental crust. The main outcome of this mechanism was massive inflow of high-temperature magma into the lithosphere forming within-crust layers of "asthenosphere," in which granite melts originated, eventually to migrate to shallower levels.

Widespread mafic and ultramafic rocks (drusites) and minor granites of 2.40–2.45 Ga age occur within the Archaean gneisses of the Belomorian fold belt. Several of these mafic–ultramafic and acid intrusions in the north-western part of that belt have been studied in detail. The mafic and ultramafic rocks are rich in Si and Mg, and also show LREE enrichment. They have ϵ Nd (2.45) values varying between +0.2 and −1.8. Assimilation-fractional crystallization (AFC) and mixing models in terms of ϵ Nd ( T )–La/Sm ratios have been evaluated for the origin of the mafic rocks. The results show that an AFC model is preferable. It involves 20–30% crustal rock assimilation by undepleted picrite magma with fractional crystallization. The granites are similar in composition to A-type (within-plate) granites. The Tupaya Bay granite pluton is characterized by geochemical layering which supports an anorogenic origin. The granites and mafic–ultramafic rocks (drusites) in the Belomorian Belt are similar in composition to coeval granites, acid and mafic volcanic rocks, mafic dykes and mafic layered intrusions within the Kola and the Karelian terrains, and can be interpreted as part of the Palaeoproterozoic igneous province connected with ascent of a mantle plume. The small sizes, corona textures and evidence for ductile deformation in the drusites are connected with their deeper level of emplacement ( P =8–12 kbar) than that of the mafic layered intrusions (2–7 kbar).

The results of detailed study of the Urosozero greenstone structure (northwestern part of the Vodlozero domain) of the Fennoscandian Shield are presented. The composition and the U-Pb zircon age of the volcanic rocks were studied. The Urosozero structure is composed mainly of mafic-felsic volcanic rocks rather than the sediments. Mafic and ultramafic volcanics were obtained under high degree source melting followed by crustal contamination. Intermediate and acid volcanics vary from andesites to rhyolites and are similar in composition to the volcanics of the Shiloss and Lake Kamennoe greenstone structures. The methamorphism of dacites occurred at T = 400–610 °С and P > 4 kbar. SIMS SHRIMP-II U-Pb dating of the dacite specimen was carried out on separate zircon grains at the Centre of Isotopic Research (VSEGEI, St. Petersburg). The ages received include 2875 ± 9 Ma as the time of volcanism and 2709 ± 8 Ma as the time of metamorphism. So, the volcanism of the Uros greenstone structure is synchronous with the volcanism of the northern Vodlozero domain.

We subdivide southeastern Karelia (Vodlozero) into two different areas on geological grounds. (1) The Vodla River area in which the metamorphic complex contains gneisses and amphibolites which yield UPb zircon ages of 3.14±0.03 Ga and 3.13±0.09 Ga, respectively. They were affected by polyphase deformation and polymetamorphism during 3.1 and 2.8 Ga events. (2) The Lay-ruchey River and Vyg River area where two groups of tonalites with UPb ages of 3.17 and 3.14 Ga can be distinguished by their major and trace element compositions. The first group is similar to some tonalites from the TTG suite in eastern Finland (Martin et al., 1983). The second group is similar to tonalites (TTG suite) from Lapland (Jahn et al., 1984). Two groups of amphibolites can also be distinguished in the Vodlozero region yielding UPb ages of 3.13 and 2.86 Ga. Geological relationships together with geochemical features show the younger group to be comparable to metabasalts from greenstone belts. Tonalites, gneisses and the older amphibolites have model Nd ages which are older than the UPb zircon ages from the same suites.

at 1^1� 5 GPa. The precise cause of the melting event at 2� 74 Ga is not known, although a model involving upwelling of asthenospheric mantle following slab break-off is consistent with the geochemical evidence for the enrichment of the Karelian subcontinental mantle lithosphere by subduction fluids.

The Karelian craton ( > 2.3 Ga ) has been recognized within the Baltic Shield. The basement of the craton is a late Archaean granite—greenstone terrain. The greenstone belts from different regions of Karelia show variations in age and composition of volcanic rocks. Two older belts ( > 2.9 Ga ) - one with multimodal volcanism and the other with bimodal volcanism - constitute the eastern part of the terrain (central and eastern Karelia). Two younger belts (2.8–2.6 Ga) with the same modal distributions of volcanic rocks make up the western part of the terrain (western Karelia and eastern Finland). According to magnetic anomaly patterns there are four types of granite—gneiss areas that separate the greenstone belts. Three types represent the greenstone basement reworked at different degrees. The fourth type corresponds to tonalites and granites surrounding the greenstone belts. The emplacement and evolution of the tonalites and granites are related to the evolution of the greenstone belts. Geochronological data on the granites of the basement demonstrate a decrease in age from E to W. Late Archaean low-pressure granulite metamorphism took place almost synchronously (2.65 Ga ago) in both the western and eastern domains.