The Tirodi Gneissic Complex (TGC) represents the basement sequence of the Central Indian Tectonic Zone (CITZ), underlying the Proterozoic supracrustal sequences of the Sausar and Betul Groups of rocks. Lithologically, the TGC constitutes a combination of pink and grey granitic gneiss assemblages, characterised by biotite-rich, hornblende-biotite-rich, and muscovite-biotite-rich granite gneiss. Compositionally, the TGC granitoids represent tonalite-trondhjemite-granodiorite to granite, and have calc-alkaline lineage with metaluminous to peraluminous characteristics. Geochemically, they dominantly belong to A2-type granitoids. Chondrite normalised REE ratios of La/Sm, La/Yb, La/Gd, and Gd/Yb indicate diverse LREE/HREE enrichment. Multi-element patterns for the TGC granitoids are characterised by light rare earth elements (LREE) and large ion lithophile elements (LILE) enrichment and depletion of high field strength elements (HFSE: Nb, P, and Ti) and strong positive Pb and Th anomalies. The observed negative anomalies for HFSE are attributed to diverse crustal/lithospheric sources, with some influence from K-feldspar, plagioclase and Ti-oxide fractionation. Sm–Nd data presents initial 143Nd/144Nd (t = 1.7 Ga) ratios (0.509898 to 0.510508), and εNd (t = 1.7 Ga) is (+ 0.58 to -10.59), with TDM model ages ranging from 2.11 to 2.95 Ga. Such a wide range of εNd (t = 1.7 Ga), indicates heterogeneous crustal/lithosphere sources, which have probably experienced longer crustal residence times. Zircon U–Pb ages for individual TGC samples are 1506 ± 11 Ma (TG-01), 1534 ± 26 Ma (MU-5), 1675 ± 9 Ma (BT-4), 1724 ± 11 Ma (BT-3), 1730 ± 13 Ma (BT-4), and 1960 ± 2 Ga (Ms-2), respectively. These ages have probably recorded the key periods of the Columbia supercontinent's assembly, growth, and breakup. Geochemical and geochronological results suggest that the TGC granitoids have a crustal/lithospheric origin and are formed by partial melting of felsic sources in dominantly VAG (volcanic arc granite) and, to some extents, WPG (within-plate granite) settings.

The Tirodi Gneissic Complex (TGC) from central India represents part of the basement gneisses. The TGC comprises a combination of pink and grey granitic gneiss assemblages, and it is petrographically characterized by biotite-rich granite gneisses. The geochemistry and isotope (Rb–Sr) data set is used to constrain the petrogenesis of TGC granitoids and Precambrian crustal evolution. Previous geochemical results from the study area were not focused on the genesis and crustal evolution of these granitoids. The present contribution addresses these issues by using new geochemical and isotopic data sets. The studied samples were analyzed by WD-XRF (Siemens SRS 3000) and ICP-MS (Perkin Elmer, Elan DRC-e) facility at Wadia Institute of Himalayan Geology Dehradun. These granitoids classified as calc-alkaline granite-trondhjemite with metaluminous to peraluminous composition. The negative correlation of ferromagnesian oxide with silica suggests primary magmatic igneous parental melt. Multi-element patterns for the TGC granitoids are characterized by large ion lithophile elements (LILE) enrichment, depletion in high field strength elements (HFSE: Nb, P and Ti) and positive Pb and Zr anomalies. Negative anomalies in HFSE correspond to crustal/lithospheric sources with some influence of K-feldspar, plagioclase and Ti-oxide fractionation. Isotopic data presents the Initial 87Sr/86Sr(t=1.6 Ga) ratio that varies from 0.70595 to 0.73191 for TGC granitoid. Such a range of initial 87Sr/86Sr ratios (> 0.706), corresponding to the TGC granitoid, indicate they are generated within the crust. The elevated value of the initial 87Sr/86Sr ratio may also correspond to the alteration. The geochemical results on the TGC granitoids indicate transitional tectonic settings from "within plate granite" to "volcanic arc syn-collisional granite".

Microstructural deformation and the age of monazite (Ce) from diatectite granite of the presumably impact Jarva-Varaka structure in the Kola Region (northeastern Fennoscandian Shield) are presented. Biotite diatectite granite forms lenses in the aluminous gneisses of the Kola group hosting the 2.5-Ga-layered Jarva-Varaka Massif (JVM). A sample of biotite granite was collected northeast of the Jarva-Varaka Massif near the earlier described pseudotachylitic breccias. BSE images revealed primary domains in monazite grains with rhythmic euhedral zoning and secondary altered domains. Backscattered electron diffraction maps of monazite grains document the development of deformation twins along {100} and {001} and plastically deformed domains with a maximum misorientation of up to 10°. Newly formed areas of recrystallization (neoblasts) cut the twins and plastically deformed domains. Monazite yielded a U-Pb age of 2706 ± 10 Ma (ID-TIMS method), which defines the crystallization age of the host diatectite granite coeval to the 2.76–2.70 Ga metamorphism of the Kola gneisses. A similar age of 2734 ± 139 Ma (ThO2*–PbO isochron) was obtained for primary monazite domains by the chemical U-Th-total Pb isochron method (CHIME). Domains altered under late hydrothermal processes yield CHIME ages of 1796–1723 Ma. Monazite neoblastic domains are close to primary domains in chemical composition and yielded CHIME ages of 2550–2519 Ma, reflecting probably an influence of the JVM formation. The data obtained are insufficient to confirm the impact origin of the Jarva-Varaka structure, which requires further investigation.

Abstract The Central Indian Tectonic Zone (CITZ) comprises northern and southern Indian cratonic blocks and is a tectonic window that is suitable for investigating the Proterozoic crustal evolution because of the presence of a wide variety of lithologies. Geochemical and geochronological data on mafic granulites by previous workers do not ascertain the possibility of mafic protoliths and their coeval link to other CITZ units. Thus, determining the precise timing of the formation of mafic granulites may indicate a connection between metamorphism and fragmentation of the Columbian supercontinent. This study presents zircon U–Pb ages, Nd isotopes and the geochemistry of mafic granulites to evaluate their genesis and timing of metamorphism. The results show the tholeiitic affinity and primary magmatic differentiation of the parental melt. Depletion of Nb, P, Zr and Ti and positive enrichment of Ba, U and Pb indicate the derivation of mafic granulites from a variably enriched subcontinental lithospheric mantle (SCLM) source. The zircon U–Pb ages (1564 ± 8 to 1598 ± 9 Ma) are interpreted as a period of granulite-facies metamorphism. The T DM (depleted-mantle) model ages (2.9–3.4 Ga) of mafic granulites indicate the timing of mafic protolith extraction. The mineral isochron age c. 1.0 Ga indicates that these rocks underwent some events during an early Neoproterozoic period. Protolith of mafic granulites could be related to the evolution of melts derived from metasomatized SCLM through fractional crystallization processes.

The Chotanagpur Gneissic Complex (CGC) is characterized by the Makrohar Granulite Belt (MGB) at its north‐western margin parallel to Son‐Narmada lineaments. The MGB exhibits a typical association of mantle‐derived mafic tholeiitic and alkaline rocks along with the felsic units. The zircon U–Pb data on the intrusive granite gneiss from this association define a crystallization age of 1,498 ± 38 Ma, representing a widespread Mesoproterozoic within‐plate magmatic event in CGC synchronous with the breakup of the Columbia Supercontinent. These granite gneisses have an alkaline affinity and are metaluminous in character. They exhibit many of the geochemical characteristics of anorogenic (A‐type) magmas, including enrichment of incompatible trace elements, like Zr, Hf, Nb, Y, Ga, and rare earth elements (REE), but low in Ba and Sr as well as high FeO t /(FeO t + MgO) (~0.98) values and Ga/Al (~3.92) ratios. They show less fractionated REE patterns, characterized by relatively enriched LREE and flat HREE with negative Eu anomaly, and have high Zr‐saturation temperatures (~955°C). Considering their field characteristics and all the geochemical and isotopic features, we conclude that they were derived from melting the lower crust metasomatized by mantle‐derived alkali‐rich fluids due to asthenospheric upwelling.

The results of geological, geochemical, and geochronological studies of granophyre rocks from the Jarva-Varaka Massif (Kola region) are presented. The 2-km section of the massif is composed of mafic and felsic norites, hypersthene diorite, pigeonite-augitic diorite, quartz diorite, and granodiorite. All these rocks contain a variable amount of granophyre (micropegmatite), from 10

Mineralogical, petrophysical and geochemical studies have been carried out to determine the sequence and formation conditions of uranium mineralization within the Litsa ore occurrence (Kola Region). Mineralogical studies show the following formation sequence of ore minerals: uraninite – sulfides – uranophane, coffinite, pitchblende. Two stages of uranium mineralization are distinguished: Th-U (1.85-1.75 Ga) and U (400-300 Ma). The distribution of physical properties of rocks in the area is consistent with the presence of two temporal stages in the formation of mineralization with different distribution and form of uranium occurrence in rocks. The factors that reduce rock anisotropy are the processes of migmatization and hydrothermal ore mineralization, which heal pores and cracks. Fluid inclusions in quartz studied by microthermometry and Raman spectroscopy contain gas, gas-liquid and aqueous inclusions of different salinity (1.7-18.4 wt.% NaCl-eq.). According to homogenization temperatures of inclusions in liquid phase, the temperature of the Paleoproterozoic and Paleozoic stages of uranium mineralization at the Litsa ore occurrence is ~ 300 and 200 °С, respectively. Correlations of the spatial distribution of elastic anisotropy index with an elevated radioactive background allow using this petrophysical feature as one of the prognostic criteria for uranium and complex uranium mineralization when carrying out uranium predictive work.

The early stages of basic–ultrabasic magmatism in Sarmatia are characterized by the appearance of ultrabasic rocks formed from the mantle with an abnormally high iron content. Therefore, it is important to study them as the source of information about the stages and causes of the activity of the mantle and its possible composition. This magmatism has been recorded in Sarmatia since the beginning of the Eoarchean. The relics of Eo- and Paleoarchean basic and ultrabasic rocks were found in the Dniester–Bug, Kursk, and Azov provinces, which underwent tectonic reconstruction in the Mesoarchean and Paleoproterozoic. Mesoarchean basic–ultrabasic magmatism is manifested in all provinces of Sarmatia and is represented by effusive and intrusive facies. The Mesoarchean greenstone belts composed of komatiites and basalts have been well preserved in the Middle Dnieper province; in other provinces, they are strongly deformed and form narrow linear structures. The Paleoproterozoic endogenous activity in Sarmatia differs from that in other regions in the almost complete absence of magmatism in the period 2.5–2.3 Ga and its significant manifestation 2.1–2.0 Ga. The magmatism in Sarmatia at this stage is similar in the ratios of basic–ultrabasic and granitoid complexes to the magmatism in South Africa but differs from that in Fennoscandia and Canada. The volume of granitoids coeval with basic rocks is larger than the volume of mantle magmatism. The igneous complexes formed 2.1–2.0 Ga in Sarmatia and South Africa are also similar in the presence of norites, the enrichment in Ni and platinum group elements, and the ratio of granitoids and basic–ultrabasic rocks. Magmatic activity (first of all, basic–ultrabasic magmatism in ancient cratons) is not a synchronous phenomenon on a planetary scale and varies greatly in the volume of produced material within the same time intervals. Early Precambrian basic–ultrabasic rocks (volcanics of greenstone belts, intrusions of large igneous provinces, and layered massifs) resulted from plumes, whose derivates formed within the lower and upper mantle and/or the upper mantle and crust, which determined the heterogeneous composition of igneous rocks. The spatial heterogeneity and nonsynchronic occurrence of basic–ultrabasic magmatism might have been due to impact events serving as the triggers of plumes.

Проведены минералогические, петрофизические и геохимические исследования для определения последовательности и условий формирования урановой минерализации в пределах Лицевского рудопроявления (Кольский регион). Минералогические исследования показывают следующую последовательность образования рудных минералов: уранинит – сульфиды – уранофан, коффинит, настуран. Выявлены две стадии урановой минерализации: Th-U (1,85-1,75 млрд лет) и U (400-300 млн лет). Распределение физических свойств пород на участке согласуется с наличием двух временных этапов в формировании оруденения с разным распределением и формой нахождения урана в породах. Фактором, снижающим анизотропию пород, являются процессы мигматизации и гидротермальной рудной минерализации, залечивающей поры и трещины. Флюидные включения в кварце, изученные методами микротермометрии и КР-спектроскопии, содержат газовые, газово-жидкие и водные включения разной солености (1,7-18,4 маc. % NaCl-экв.). Согласно температурам гомогенизации включений в жидкую фазу, температура палеопротерозойского и палеозойского этапов урановой минерализации на Лицевском рудопроявлении составляет ~ 300 и 200 °С соответственно. Корреляции пространственного распределения показателя упругой анизотропии с повышенным радиоактивным фоном позволяет использовать этот петрофизический признак в качестве одного из прогнозных критериев уранового и комплексного уранового оруденения при проведении прогнозных на уран работ.

Аннотация. На примере палеопротерозойского Мончегорского расслоенного комплекса предлагает

The Central Indian Tectonic Zone (CITZ) is major E-W trending suture zone between Northern and Southern Indian crustal blocks. The southern portion of the CITZ comprises three litho-tectonic units: Tirodi Gneissic Complex (TGC), Sausar Mobile Belt (SMB) and Bhandara-Balaghat Granulite Belt (BBGB). Elemental and isotopic data are used to constrain the genesis of granitoids and their protoliths, which may help us to understand the Proterozoic crustal evolution in CITZ. Geochemical and isotopic results are consistent with previous studies that these granitoid plutons are linked to the felsic magmatism of the Columbian crustal assembly in India, North America and North China. Granitoids varies from tonalite to granite, alkalic to calcic, metaluminous to peraluminous composition. Normalized elemental ratios of La/Sm, La/Yb, La/Lu, and Gd/Yb depict variable LREE enrichments and varying degrees of partial melting of heterogeneous crustal/lithospheric sources. The studied rocks are characterized by positive anomalies for Pb and negative anomalies for Nb, Sr, P, Ti, which indicate the influence of subduction-zone fluids in the source regions. Negative anomalies for K, Sr, and Ti for SMB and BBGB granitoids may also be attributed to K-feldspar, plagioclase, and Fe-Ti oxide fractionation. However, TGC porphyritic leucogranites display K, Ba and Eu positive anomalies, probably related to the accumulation of K-feldspar phenocrysts. Nd-Sr data presents initial ratios of Nd-143/Nd-144 t = 1.6 Ga ranges between 0.509961 and 0.510300; eNd t = 1.6 Ga ranges from -5.3 to -11.9 with TDM ages ranging from 2.20 to 2.78 Ga for TGC granitoid. The ratios of Nd-143/Nd-144 t = 1.6 Ga ranges between 0.510232 and 0.510985; epsilon(Nd) t = 1.6 Ga ranges from +0.2 to +8.2 and T-DM ages varies from 1.5 to 3.0 Ga. The initial Sr-87/Sr-86 t = 1.6 Ga ratios ranges between 0.699834 and 0.797151 for SMB granitoid. However, BBGB granitoids show the ratios of Nd-143/Nd-144 t = 1.6 Ga ranges between 0.509752 and 0.510910; epsilon(Nd) t = 1.6 Ga ranges from +6.7 to -16, and TDM ages range from 1.51 to 3.29 Ga. The initial Sr-87/Sr-86 (t = 1.6 Ga) ratios varies between 0.705096 and 0.717440. These ranges of epsilon(Nd) (t) and T-DM values possibly indicate their derivation from enriched and heterogeneous crustal/ lithospheric sources, and minor components from depleted lithospheric sources.

Signs of shock metamorphism in rocks and minerals of the layered Jarva-varaka massif and the host rocks are described. The massif is located in the Monchegorsk ore district of the Kola region. Signs of the impact genesis of the massif include pseudotachylite breccia, “kink-banding” structures in biotite and clinozoisite, planar deformations in quartz, diaplectic glasses of zircon, sillimanite, and plagioclase, and deformation microstructures in monazite. The totality of available features allows us to assume the impact origin of the Jarva-Varaka massif ca. 2.5 Ga ago.

We study the P–T conditions and age of metamorphic evolution of the rocks that make up the Korvatundra structure in the northeast of the Fennoscandian Shield. The rocks underwent progressive metamorphism of the amphibolite facies at 625–660 ºC and 8.7–8.8 kbar 1945 ± 34 Ma (Sm–Nd data). The pegmatite cutting the metamorphic paragenesis that formed at this stage has an age of 1917 ± 6 Ma (zircon U–Pb data). Metamorphic transformations after 1917 Ma are manifested locally as discrete zones of blastomylonites in the rocks of the northern part and some inner sites of the Korvatundra structure. Both local increases and decreases in temperature and pressure are possible in these zones. The formation of light titanite with an age of 1863 ± 44 Ma marks the next stage of shear strain. Low-temperature alterations (chloritization and silicification) took place in the zones of final deformations 1722 ± 5 Ma (Rb–Sr data). Beginning from 1.94 Ga, the general deformational and metamorphic history of the Korvatundra structure, Lapland Granulite Belt, and Tana Belt confirms the assumption of the formation of a single inverted metamorphic zoning within the Korvatundra structure and the overlying Lapland–Kolvitsa Collision Belt in the Paleoproterozoic. The obtained data supplement the idea of the Paleoproterozoic geodynamic evolution of the Lapland–Kola orogen.

It is proposed to distinguish two genetic types of primary magmatic contact-style PGE-Cu-Ni mineralization using the example of the Monchegorsk Complex: 1) "gravitational" and 2) "intrusive". The presentation discusses features of the formation of these two types of the mineralization with an emphasis on their potential economic significance.

Аннотация.Описаны микроструктуры деформации в монаците-(Ce) из диатектических гранитов предполагаемой импактной структуры Ярва-варака на Кольском полуострове.Используя дифракцию обратно-рассеянных электронов в монаците-(Ce) были установлены деформационные двойники по оси [100] и пластически-деформированные домены с максимальной разориентировкой до 10 °.Также обнаружены необласты -новообразованные участки локальной перекристаллизации, сохраняющие ориентировку исходного зерна и пересекающие двойники и пластически-деформированные домены.Подобные деформационные признаки в монаците известны в импактных структурах Вредефорт (Африка) и Яррабубба (

Studying early Precambrian astroblems is complicated by their localization in structural and compositional complexes that underwent superimposed metamorphism and tectonic processing. Back in the 1980s, seven sites with occurrences of breccias and other rocks resembling impact structures were identified as potentially diamondiferous impact structures within the Karelian-Kola region. But at present, only two astroblems are known in the region: Janisjärvi of 725 ± 5 Ma and Suavjärvi of ~2400 Ma. In the Kola part, impact origin is assumed for two objects: the Javrozero circle structure in the Tanaelv belt and the Järva-varaka layered massif in the Monchegorsk ore area. The most promising structure to be an astrobleme with serious signs of impact origin is the Paleoproterozoic Järva-varaka massif. According to geological, petrochemical, and geochemical characteristics of rocks the Järva-varaka massif is most similar to the 1.85 Ga Sudbury structure (Canada), for which an impact origin was assumed. Shock metamorphism of the Järva-varaka massif was manifested in amorphization of zircon from the country rocks with formation of plagioclase and sillimanite glasses in inclusions, as well as planar deformations in quartz.

The Vulvara anorthosites occur among the rocks of intermediate composition, in contrast to most Lapland granulite belt (LGB) anorthosites, associated with mafic granulites. The U-Pb, Sm-Nd and REE geochemical data were used to compare Vulvara with other LGB anorthosites. The intrusion of the Vulvara massif occurred in the interval of 2100-1965 Ma. The first metamorphic processing took place 1947 +/- 11 Ma ago under granulite facies. Postgranulite transformations occurred 1900-1850 Ma ago under amphibolite facies; earlier (1896 +/- 15 Ma) and later (1852 +/- 17 Ma, 1846 +/- 16 Ma) thermal events were established. The Vulvara anorthosites, in comparison with other LGB anorthosites, are distinguished by a more acidic composition of plagioclase, a higher F number of rocks and mafic minerals, a higher content of SiO2, Na2O, K2O, Ba, Sr, Zr, Nb, Rb, and a lower content of CaO. The Sm-Nd and REE geochemistry suggest that there are three groups of LGB anorthosites, distinguished both by age and magma source.

Следы импактных событий в архее Побужского гранулито-гнейсового комплекса Украинского щитаЛобач-Жученко С.Б. 1 , Каулина Т