The paper discusses the melt sources and formation parameters of the Khokhol-Repyevka granitoid batholith that compose the Don terrane of the Volga–Don orogen in the East European craton. The batholith consists of three granitoid types: Pavlovsk granitoids (quartz monzonites–granites, mostly without pyroxenes), Potudan granitoids (quartz monzogabbro–granodiorites containing pyroxene), and hybrid ones (quartz monzodiorites, monzonites, and quartz monzonites). These three types of rocks occur together and have a similar age of 2050–2080 Ma, similar geochemical characteristics (high contents of Ba, Sr, and highly fractionated REE patterns with GdN/YbN = 2–11), but differ in petrographic and isotopic geochemical parameters. The initial isotope characteristics of the sources of the Pavlovsk-type rocks are εNd(t) = +0.2 to ‒3.7 and Sri = 0.70335, those of the Potudan type are εNd(t) = –1.7 to –3.8, Sri = 0.70381–0.70910, and the hybrid rocks have εNd(t) = –8.8, Sri = 0.70596. In addition to granitoids, the batholith was found out to host two types of leucogranite dikes. One of them is characterized by εNd(t) = –3.8 and fractionated HREE patterns (GdN/YbN = 2.1–3.8) and could be formed as a result of the deep differentiation of Pavlovsk-type magma. The other type has εNd(t) = –7.8 and less fractionated HREE patterns (GdN/YbN = 1.1–1.6), which likely resulted from the melting of a crustal source at shallow depths. The Rb–Sr isotope-geochemical characteristics of rocks of the Pavlovsk and Potudan types indicate that their melts were derived from different sources. Therefore the melts of the Khokhol–Repyevka batholith were derived from at least three sources: (1) lower (or buried oceanic) crust of predominantly mafic composition and/or enriched mantle, which was metasomatized in the Proterozoic, whose involvement is reflected in the composition of the Pavlovsk granitoids; (2) an enriched mantle source, which was likely subcontinental lithospheric mantle (SCLM) that had been metasomatized during an earlier stage of the geological development of the region, specific of the Potudan-type monzonitoids; and (3) Archean crust consisting mostly of TTG gneisses and metasediments, which underwent melting and participated in the formation of some of the leucogranite dikes and hybrid rocks. The results of thermodynamic modeling indicate that the mixing of two melts contrasting in composition (Potudan-type mafic and Pavlovsk-type intermediate–felsic) could form only some of the hybrid rocks. The others could be formed by mafic melt contaminated with anatectic melts derived from the Archean crust of the Kursk block.

Mineral reactions were studied in metamorphic rocks from the Meyeri tectonic zone, and the P–T path of the development of this structure was calculated. According to the P–T path, the Proterozoic granulite complex of the Svecofennian Belt was thrust onto low-temperature rocks of the Archean Karelian Craton. Relict staurolite and other minerals preserved as inclusions in the garnet porphyroblasts made it possible to identify the pre-peak stage of metamorphism with P–T parameters no higher than the low-temperature amphibolite facies of moderate and low pressure. The peak metamorphic conditions of the tectonic zone are estimated at T > 700°C and P 7 kbar using the composition of relict minerals, while the temperature on the prograde trend of metamorphism was 500–600°C at a pressure of about 5 kbar. The post-peak stage began with a distinct decompressional P–T path at the aforementioned high temperatures, with a change from granulite hypersthene-containing assemblages to lower-temperature hydrous ones. The subsequent metamorphic retrogression was characterized by the development of numerous hydrous minerals as a result of the activation of fluids in the shear zone. The P–T path of the tectonic zone is clockwise and reflects the exhumation of the Svecofennian granulite complex during the orogenic events.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23070243

This paper presents the results of a study of isotopic systems in minerals and rocks in southern margin of the epi-Archean Karelian craton in the zone of its junction with the Svecofennian mobile belt. U-Pb, Sm-Nd and Rb-Sr mineral ages of metamorphic rocks allowed reconstructing a T-t trend during ~1.88–1.61 Ga, which reflects a wide-ranging cooling history of metamorphic rocks from the peak values of about 650–700 °C at 1.88–1.79 Ga (U-Pb age of monazites and apparent oldest Sm-Nd age of amphiboles) to 300–400 °C at 1.61 Ga (model Rb-Sr age of biotites) in zones of low- and medium-temperature metamorphism. The specificity of removal of deep-seated rocks to the present-day erosion surface and the reconstructed T-t trend comply with the development of thrust-nappe structures during the exhumation of the Svecofennids. It is also assumed that differential vertical block movements played a significant role during the post-orogenic extensional collapse and neorifting.

We discuss the rocks of the Larba granulite block in the Ilikan zone of the Dzhugdzhur-Stanovoi superterrane. The Larba block is dominated by basic schists and garnet-biotite-orthopyroxene and garnet-biotite-cordierite-sillimanite gneisses (metabasites and metapelites). Calculation of temperatures and pressures of mineral formation was carried out by multi-equilibrium geothermobarometry, which makes it possible to evaluate the degree of equilibrium of mineral compositions along with P-T parameters. The P-T estimates have shown metamorphism of aluminous gneisses under moderate-pressure granulite facies conditions (7-8 kbar, 800-850 degrees C). Orthopyroxene granulites formed under granulite-amphibolite transition facies conditions. The mineral compositions and parageneses in highly ferrous metabasites permitted estimation of the conditions of metamorphism, P = 4-5 kbar and T = 630-700 degrees C, and show no influence of earlier granulite facies metamorphism. The bimodal P-T distribution for most samples of aluminous gneisses most probably reflects progressive and near-peak conditions of granulite metamorphism. The time of enderbite magmatism is determined from the upper intercept of discordia with concordia at 2546 +/- 52 Ma and should be verified. The age of metamorphic rims over enderbite zircon is 1882 +/- 11 Ma. The model Nd age of enderbites, TNd(DM) = 2.57-2.58 Ga, is close to the age of the core of enderbite zircon and differs significantly from the model Nd age of the host metamorphic rocks (2.8-3.0 Ga). The Paleoproterozoic metamorphism of the Larba block rocks regionally coincides with the third stage of collisional granitoid magmatism of the southeastern Siberian craton and records the formation of this structure.

The article focuses on the issues related to the primary nature and metamorphism of gneisses from the Larba block of the Dzhugdzhur-Stanovoy fold area, which are based on the study of the mineralogical composition of supracrustal rocks. PT-parameters for the highest temperature and pressure metamorphic transformations of rocks of the Larba block are estimated as P = 6.5–8.5 kbar and T > 800°C. Relatively low-temperature garnet-biotite, garnet-biotite-chlorite mineral parageneses were formed at the regressive stage of metamorphism at ~4–6 kbar and temperatures up to 500–600°C. Wide variations in paragneiss compositions indicate that protoliths of the studied gneisses differed in composition. Overall, Larba metasedimentary rocks had weakly and moderately weathered source areas. Most of the compositions of paragneisses are localized in the field of chlorite-montmorillonite, montmorillonite-kaolinite-hydromica and chlorite clays formed from the mafic substrate. Low alkalinity in combination with a high MgO content indicates the presence of rock erosion products with a significant admixture of basic volcanic material in the detrital material. Migmatization of rocks is the most significant factor distorting the reconstruction of the original rock composition.

Morphology and compositions of minerals in metamorphized Early Proterozoic gabbroids of the Northern Ladoga area were studied with the purpose to identify criteria of their magmatic or metamorphic origin. These rock-forming minerals of the Kaalamsky complex are stable in the wide range of temperatures and pressure. To solve the problem, together with comparison with minerals from non-metamorphized rocks of the Potudan intrusion (Volga-Don orogen), there were used the data of petrographic study in as well as the data of mineral compositions and thermodynamic modeling. It was concluded that it is possible to distinguish groups of magmatic and metamorphic rock-forming minerals with help of morphogenetic, geochemical, and thermobarometric criteria, as well as criteria based on revealing the concordance between observed and modeled mineral compositions. Combined application of these criteria has allowed determining that rocks of Kaalamsky complex contain olivine, clinopyroxenes, amphiboles, plagioclases of magmatic origin, and also their metamorphic analogues.

The paper discusses the possible conditions and involvement of sources in genesis of the Khokhol-Repyevka batholith granitoids, that build up the Don terrane in the Volga-Don orogen of the East European Craton. In the batholith, three types of granitoids are distinguished – pavlovsk (quartz monzodiorite–granites, mainly pyroxene-free), potudan (quartz monzogabbro–granodiorites containing pyroxene) and hybrid (quartz monzodiorites, monzonites, quartz monzonites). These three types of rocks are spaсely co-located and have a similar age of formation 2050–2080 Ma, similar geochemical characteristics (high contents of Ba, Sr, highly fractionated REE patterns (GdN/YbN= 2–11)), however, they differ in petrographic and isotopic geochemical parameters. Primary isotope characteristics of sources for rocks of the pavlovsk type εNd(t) = +0.2…–3.7, Sri= 0.70335, for potudan εNd(t) = – 1.7 ... –3.8, Sri= 0.70381–0.70910, for hybrid εNd(t) = – 8.8, Sri= 0.70596. Apart from granitoids, two types of leucogranite dikes were found in the batholith. The first type is characterized by εNd(t) = –3.8 and fractionated HREE patterns (GdN/YbN= 2.1–3.8) and could have formed as a result of deep differentiation of pavlovsk-type magma. The second type is with εNd(t) = –7.8 and less fractionated HREE patterns (GdN/YbN = 1.1–1.6), which presumably appeared as a result of melting of a crustal source at shallow depths. Rb-Sr isotope-geochemical characteristics of rocks of the pavlovsk and potudan types indicate their formation from different sources. In total, at least three sources took part in the formation of the Khokhol-Repyevka batholith: 1) lower (or buried oceanic) crust, predominantly of mafic composition and/or enriched mantle, metasomatized in the Proterozoic, the participation of which is reflected in the composition of the Pavlovsk granitoids; 2) an enriched mantle source, probably represented by subcontinental lithospheric mantle (SCLM), possibly metasomatized during the previous stage of geological development of the region, specific for Potudan-type monzonitoids; 3) Archean crust, consisting mainly of TTG gneisses and metasediments, which underwent melting and participated in the formation of part of the leucogranite dikes and hybrid rocks. The results of thermodynamic modeling indicate that the mixing of two melts contrasting in composition – mafic (potudan-type) and intermediate-felsic (pavlovsk-type) can lead to the formation of only part of the composition of hybrid rocks. The formation of the rest was influenced by the contamination of mafic melt by anatectic melts from the Archean crust of the Kursk block.

The Early Proterozoic gabbros of the Velimyaki intrusion of the Northern Ladoga region contain titanomagnetite ore, which has been mined as early as the end of the 19th century. Titanomagnetite horizons are enriched in phosphorus in form of apatite reaching 10 vol

Polymigmatites in the Early Proterozoic metamorphic complex of the Northern Ladoga area trace the evolution of thermodynamic conditions during anatexis. The P-T conditions inferred for anatectic leucosome correspond to the onset of partial melting under granulite facies conditions of 5.5-6.2 kbar and 720-810 degrees C. After the peak of metamorphism, pressure and temperature show a coupled decrease to 4 kbar and similar to 550 degrees C, respectively. The latest granitic veins were intruded into metamorphic rocks during an event of brittle deformation. The P-T trend correlates with changes in migmatitic mineral assemblages and in chemistry of minerals. Newly formed leucocratic material changed from plagiogranitic to granitic composition when melting involved plagiogneiss but melt derived from Al-rich metapelite remained granitic. The analyzed leucosomes and granitic veins originated by multistage melting, under P-T conditions changing from granulite to amphibolite facies, between 1875 and 1865 Ma. Judging by their ages, the leucosome and granitic vein bodies from the Lakhdenpokhia and Priozersky zones of the area differed in the total duration of crystallization. Therefore, a single thermal event involving different lithologies can produce intrusions of different ages.

—The paper reports mineral chemistry, whole-rock major and trace element composition, structure, and geological setting of the phlogopite peridotite lens within the Bug granulite–gneiss terrane of the Dniester–Bug Province, Ukrainian Shield. Geochemical features of the studied peridotites and minerals indicate a complex evolution of the lens. The early stage is marked by the crystallization of olivine + spinel (Al-chromite) cumulus from melt of supposably picritic composition, and further crystallization of clinopyroxene. The melt shows signs of hybridization by host gneissic enderbite. Orthopyroxene crystallized later and frequently replaces clinopyroxene. The phlogopite cystallization is likely related to the fluid activity and the growth of potassium potential in the fluid. Granulite-facies metamorphism accompanied by ductile deformations affected the mineral asseblage and chemical compositions of peridotites and orthopyroxenites. At the final stage, the rocks and minerals experienced retrograde metamorphism and local foliation of the rocks.

In addition to the widespread Fe-Mg staurolite, typical for medium-temperature high-alumina metapelites, there are a number of finds of magnesian staurolite in metamorphosed mafic rocks – metabasites. Based on thermodynamic modeling and analysis of the mineral formation patterns, the most significant factors of the staurolite formation in metabasites have been revealed. For the formation of staurolite in metabasites, in contrast to staurolite in low- and medium-pressure metapelites, medium- and high-pressure conditions of metamorphism are necessary. An increase in the proportion of carbon dioxide in the composition of the water-carbon dioxide fluid has practically no effect on staurolite-forming mineral reactions, but leads to their shift to lower temperatures and higher pressures. Al, Fe, Mg, Ca are critical petrogenic rock components for the formation of magnesian staurolite, the contents and ratios of which primarily determine the stability of staurolite in metabasites. To understand the regularities of mineral formation, it seems appropriate to divide metabasites into subgroups of predominantly magnesian, iron-magnesian, and ferruginous protoliths. Based on this division, three petrochemical modules are proposed in the form of the ratio of rock-forming components: MgO/CaO, CaO/FM, Al2O3/FM, based on which it is possible to predict the appearance of staurolite in the basic rock when the corresponding P-T conditions of metamorphism are reached.

. Geological examples of the development of thermal dome structures in the Svecofennian belt demonstrate the relationship between plutonic and metamorphic events and metamorphic strengthening towards the core parts of the structures. The corresponding 2D geological model has been created to make a quantitative assessment of the effect of mantle magmas temperature at the base of the crust and the formation of the diapiric cores surrounded by high-temperature areas with a degree of granulite facies metamorphism. Modeling shows that there is a possibility of melting of the lower crust in the presence of a water fluid under the influence of mantle magmas. After melting, there occurs an ascent of partially molten material towards the upper crustal levels. An absorbed aqueous fluid changes to hydrous melt, thus lowering its viscosity and density. The ascending height of high-temperature cores is determined by the depth of viscous-to-elastoplastic transition in the crustal matter rheology. These materials ascend to upper levels in a partially molten state in the process of overthrusting due to "collisional" tectonics.

In addition to the widespread Fe-Mg staurolite, typical for medium-temperature high-alumina metapelites, there are a number of finds of magnesian staurolite in metamorphosed mafic rocks – metabasites. Based on thermodynamic modeling and analysis of the mineral formation patterns, the most significant factors of the staurolite formation in metabasites have been revealed. For the formation of staurolite in metabasites, in contrast to staurolite in low- and medium-pressure metapelites, medium- and high-pressure conditions of metamorphism are necessary. An increase in the proportion of carbon dioxide in the composition of the water-carbon dioxide fluid has practically no effect on staurolite-forming mineral reactions, but leads to their shift to lower temperatures and higher pressures. Al, Fe, Mg, Ca are critical petrogenic rock components for the formation of magnesian staurolite, the contents and ratios of which primarily determine the stability of staurolite in metabasites. To understand the regularities of mineral formation, it seems appropriate to divide metabasites into subgroups of predominantly magnesian, iron-magnesian, and ferruginous protoliths. Based on this division, three petrochemical modules are proposed in the form of the ratio of rock-forming components: MgO/CaO, CaO/FM, Al2O3/FM, based on which it is possible to predict the appearance of staurolite in the basic rock when the corresponding P-T conditions of metamorphism are reached.

Fe–Mg staurolite is a typical and widespread mineral of medium-temperature high-alumina metapelites, whereas magnesian staurolite is only relatively rarely found in metamorphosed mafic rocks (metabasites). The most significant factors controlling staurolite stability in metabasites were identified by thermodynamic modeling and analysis of the common features of the mineral-forming processes. In contrast to staurolite in low- and medium-pressure metapelites, staurolite in metabasites is stable at medium- and high-pressure metamorphism. An increase in the proportion of carbon dioxide in the water–carbon dioxide fluid shifts the staurolite-forming mineral reactions to lower temperatures and higher pressures. Al, Fe, Mg, and Ca are the major components of rocks that are critically important for the formation of magnesian staurolite in these rocks, and the contents and ratios of these components are of crucial importance for the stability of staurolite in metabasites. To understand the processes forming the mineral in metabasites, it is instrumental to subdivide metabasites into subgroups of predominantly magnesian, ferruginous–magnesian, and ferruginous protoliths. With regard to this subdivision, three petrochemical modules are proposed in the form of ratios of major components: MgO/CaO, CaO/FM, and Al 2 O 3 /FM, based on which it is possible to predict the stability of staurolite in mafic rocks at appropriate P–T parameters of metamorphism.