The Paleoarchean age (3.34 Ga) of subalkali granite magmatism first established for the Kukhtui uplift of the Okhotsk Massif suggests a formation time of the mature continental K-rich crust in this region as early as the Paleoarchean. According to the geological structural, mineralogical–geochemical, geochronological, and isotopic–geochemical data, the Kukhtui uplift can be considered as the most ancient Paleoarchean province in Russia: the ancient consolidation core of the sialic protocrust of the Okhotsk–Omolon Craton.

Показано, что подход к периодизации событий высокоградного метаморфизма через датирование мигматитов достаточно продуктивен. В данном случае удалось выделить два таких события - 2500 и 2700 млн лет, оценить возраст изверженного протолита для древнейших в Беломорском поясе тоналитовых гнейсов и ассоциирующих с ними метагабброидов. По верхнему пересечению конкордии с дискордией из них для ядер циркона определён возраст 2796 ± 63 млн лет, который мало отличается от кайм роста ритмично зонального призматического циркона (2816 ± 110 млн лет). Линейная аппроксимация всех измеренных точек даёт верхнее пересечение 2803 ± 55 млн лет. Погрешность этих оценок высока по вполне понятной причине, однако её необходимо принимать во внимание при анализе геодинамических режимов развития неоархейских эндогенных процессов.

The β-factors of corundum were estimated on the basis of DFT calculations of vibrational frequency changes due to 16O–18O isotope substitution in a harmonic approximation using an all-electron Gaussian-type basis set and the B3LYP hybrid functional (the CRYSTAL program). Calculations were performed accounting for eight phonon wave vectors within the first Brillouin zone. The results are approximated by the relation 1000ln β crn = 9.19874x–0.12326x 2 + 0.00213x 3 (x = 106/T(K)2, 400 < T(K) < 1300), which can be used in isotope geochemical studies in combination with the known temperature effects on the β-factors of other phases.

Выполнены геохимические и изотопно-геохимические Sm-Nd-исследования сынныритов, сиенитов Сыннырского и высококалиевых сиенитов Тасского массивов позднего палеозоя, которые относятся к одной из крупнейших в мире провинций проявления внутриплитного высококалиевого и ультракалиевого магматизма. Показано, что их формирование связано с переработкой докембрийской континентальной коры Сибирского кратона и Центрально-Азиатского складчатого пояса, в связи с воздействием Сибирского мантийного плюма.

Изучены Pb-изотопные системы калиевого полевого шпата, пирита, пирротина из габброидов и руд раннепротерозойского массива Велимяки в юго-восточной части Фенноскандинавского щита. Изохронный Pb-Pb-возраст сульфидов определен как ~450 млн лет, что соответствует пересечению линии регрессии с кривой накопления свинца с = 10,4-10,8; модельный Pb-возраст сульфидов близок к изохронному при условии, что изотопный состав Pb эволюционировал из геохимического резервуара возраста 1,9 млрд лет. Изотопные параметры Pb сульфидов и калиевого полевого шпата указывают на формирование их в верхнекоровых условиях ( = U/Pb > 10). Из полученных данных следует, что изотопный состав Pb калиевого полевого шпата отвечает протерозойскому времени (1890 млн лет) магматической кристаллизации пород массива, а сильно радиогенные свинцы сульфидов с наибольшей вероятностью свидетельствуют о более позднем (каледонском) времени формирования сульфидных руд.

The Hf-Nd isotope systematics was used to determine the genesis of zircons from granulites of the Daldyn Group of the Anabar Shield. Obtained age of magmatic crystallization for biotite–hypersthene crystalline schists and garnet amphibolites agree with position of zircons within terrestrial array. Magmatic genesis of plagiogranite neosome under granulite conditions was established for leucocratic plagiogneisses.

U-Pb age and isotope-geochemical features were determined for zircon from kyanite gneisses and amphibolites of the Chupa Sequence of the Belomorian mobile belt (BMB) of the Fennoscandian shield. The cores of the zircon from the gneisses marks the Neoarchean events within 2700–2800 Ma known in the BMB, while those of the amphibolites correspond to the age of magmatic crystallization (2775 ± 12 Ma). The inner rims of zircon from the amphibolites and gneisses likely record two different Neoarchean metamorphic events (2650 ± 8 and 2599 ± 10 Ma, respectively). The outer rims record Paleoproterozoic metamorphism with an age of 1890 Ma, which formed the modern appearance and mineral assemblages of the rock association. The value of δ18O in the zircon from the gneiss is 8.6‰ in cores, slightly decreases to 8.0‰ in inner rims, and sharply decreases to 3.9‰ in outer rims. The value of δ18O in the zircon from the amphibolite is around 6.2‰ in cores, increases up to 8.6 in inner rims, and decreases to 5.2‰ in outer rims. A significant decrease of δ18O is likely related to the anomalous composition of Svecofennian metamorphic fluid restricted to local shear zones. The geochemical features of the zircons in combination with their morphology and anatomy make it possible to distinguish zircon generations of different age and change in metamorphic environments.

Комплексное изучение U-Pb-, Lu-Hf-систем циркона лерцолитовой линзы в архейских гнейсоэндербитах Побужского комплекса Украинского щита показало, что магма ультраосновного состава была контаминирована материалом вмещающих гнейсоэндербитов. Возраст циркона 2,81 ± 0,05 млрд лет отвечает времени ультраосновного магматизма в пределах Побужского комплекса. Ранее этот пик эндогенной активности исследователи рассматривали только как этап проявления метаморфизма и магматизма основного состава.

It is proved that dating high-grade metamorphism events through dating of migmatites is quite efficient. Our investigation has made it possible to identify two events of 2500 and 2700 Ma and to estimate the age of an igneous protolith for both tonalite gneiss, the most ancient in the Belomorian belt, and related metagabbroid. Based on the upper crossing of the concordia and the discordia, the zircon core age is estimated at 2796 ± 63 Ma; this age is slightly different from that of a growth rim of rhythmically zoned prismatic zircon (2816 ± 110 Ma). A linear approximation of all measured points yields an upper crossing of 2803 ± 55 Ma. The error of these estimates is high for quite understandable reasons, and yet it should be taken into account when analyzing the geodynamic development regimes of Neo-Archaean endogenic processes.

Geochemical and Sm–Nd isotope–geochemical studies of synnyrite and syenite from the Synnyr massif and high-K syenite from the Tas massif of the Late Paleozoic (eastern Siberia) corresponding to one of the largest provinces of high-K and ultrapotassic magmatism worldwide are performed. It is shown that their formation was controlled by transformation of the Precambrian continental crust of the Siberian Craton and Central Asian Mobile Belt under the influence of the Siberian mantle plume.

We have studied Pb isotopic systems of K-feldspar, pyrite, and pyrrhotine from gabbroids and ore of the Velimyaki Early Proterozoic massif in the northern Ladoga region in the southeastern part of the Fennoscandian Shield. The isochronous Pb–Pb age of sulfides has been determined as ∼450 Ma, which corresponds to intersection of the regression line with the lead accumulation curve with μ = 10.4–10.8; the model Pb age of sulfides is close to isochronous under the condition that the composition of lead evolved from a geochemical reservoir with an age of 1.9 Ga. The isotopic parameters of the lead in sulfides and K-feldspar indicate their formation in upper crust conditions (μ = 238U/204Pb > 10). From the obtained data, it follows that the isotopic composition of lead in K-feldspar corresponds to a Proterozoic age (1890 Ma) of magmatic crystallization of the rocks in the massif, and strongly radiogenic lead sulfides testify, with the greatest probability, to the later (Caledonian) formation of sulfide ores.

The isotopic–geochemical features of late and postorogenic granites of the S type and ambient migmatites are studied within the Russian part of the Svecofennian orogen of the Fennoscandinavian Shield. The spatial association of leucosomes of migmatites and granites of the S type and their similar petro- and geochemistry and distribution of Pb isotopes are evidence of the genetic similarity of their parental melts. The Borodinskoe pluton has a more primitive 206Pb/207Pb ratio, which indicates the presence of upper and U-poor lower crustal material in the source of granitic magmas. This conclusion is supported by the ɛNt(t) lower value of granites of this pluton relative to those of other plutons of the region.

The geochemical similarity and almost simultaneous (2055–2060 Ma) formation of Utakachan gabbro-amphibolite, Jagdakin granodiorite-diorite, Khoyunda granitoid, and Tygymyt leucogranite complexes, which inruded metamorphic formations of the Batomga Group are evidence of their formaton from unified magmatic source. All this makes it possibble to combine aforementioned complexes into the unified Early Proterozoic diferentiated gabbro-diorite-granite complex.

Multiple repetitions of migmatization processes are an important indication of the polychronous evolution of Precambrian Mobile Belts: this is certainly true for the Belomorian Belt. In the Belomorian Province of the Fennoscandian Shield, newly obtained data demonstrate the effect of two stages of melting of the Earth’s crust under conditions of higher pressure up to 8–14 kbar. The early stage of the migmatization and genetically related leucogranite formation took place in the Neoarchaean (2710 ± 15 and 2706 ± 14 Ma, U–Pb zircon ages), while the younger one happened in the Palaeoproterozoic (1944 ± 12 and 1882 ± 9 Ma, U–Pb zircon ages of leucosomes). The early stage of crust melting is related to collision in the Belomorian Neoarchaean orogen, while the later stage occurred during formation of the Lapland–Kola orogen.