A thermodynamic model of the ternary fluid system H2O–LiCl–NaCl is proposed for the temperature range from –77 to +300°C. This model incorporates low-temperature phase transitions of freezing products of water–salt inclusions. The model is based on the Pitzer equations using new interaction parameters of Na, Cl, and the corresponding equilibrium constants of reactions involving the solid and liquid phases. Based on microthermometry data of fluid inclusions (T of phase transitions during heating after freezing), the model allows determination of the salt concentrations. The characteristics (T, wt E 1pt” (ice + LiCl · 5H2O + NaCl · 2H2O), peritectic P_1^” (LiCl · 5H2O + NaCl · 2H2O + NaCl) and P_2^” (LiCl · 5H2O + LiCl · 3H2O + NaCl), and the cotectic, peritectic curves separating the phase fields (ice + L, NaCl · 2H2O + L, NaCl + L), as well as solubility isotherms of ice, hydrohalite, and halite calculated by the model, showed good agreement with the experimental data. As an example of the application of a model to a natural object, we determined the salt contents in lithium-bearing brine inclusions in late quartz veins of the Bolshie Keivy area (Fennoscandian Shield).

Properties of fluids under P–T conditions of the middle crust were studied with reference to the metasomatic alteration of metamorphic rocks (amphibolite facies) of the Bolshie Keivy nappe of the Keivy terrane of the Belomorian–Lapland collision orogen of the Fennoscandian shield. Properties of the fluids were studied in five selected types of rocks: metamorphic schists and gneisses with graphite, metasomatic quartz rocks with a high content of graphite, kyanite–quartz veins with wall-rock metasomatites, and metasomatic quartz-bearing kyanite rocks and anchimonomineral quartz veins. NaCl, CaCl2, CO2, N2, CH4, heavier hydrocarbons, and graphite were identified in the fluid inclusions using microthermometry and Raman spectroscopy. Using the method of multiequilibrium thermobarometry for mineral associations and the density of CO2 inclusions, a retrograde P–T path was calculated, which reflects the P–T exhumation history of the rocks. An explanation was proposed for the presence of water inclusions with NaCl of low salinity among inclusions of high salinity with NaCl and CaCl2. Comparison of data on the H2O activity (inferred from mineral equilibria) and salt content (data on fluid inclusions) with those of a model fluid (thermodynamic model of the H2O–NaCl–CaCl2–CO2 system) showed a good agreement between natural and model data. Natural and model data were synthesized to analyze variations in the phase state and chemical composition, fluid properties, including H2O activity, density, and salinity along the retrograde P–T trend.

The paper presents results of a study of middle crustal (amphibolite-facies level) desilicated rocks exemplified by corundum-bearing plagioclasites developing after metabasites at the unique Khitostrov corundum deposit in the Belomorian–Lapland orogen of the Fennoscandian shield, with emphasis placed onto newly acquired geological data, documentation and analysis of the metasomatic zoning, determination of the P–T conditions of its formation, and a model of the metasomatic process.

Properties of fluids in high-pressure granulites were studied in HP granulites (~8.7–11 kbar, ~800–900°С) and syngranulite fluid infiltration-driven HP metasomatites (~11–9 kbar, ~920–850°С) from the Lapland granulite belt of the Fennoscandian Shield. The study involved large-scale mapping of the rocks, microthermometry of mineral-hosted fluid inclusions, multiequilibrium mineral thermobarometry, and calculations of H2O activity based on mineral equilibria. The mafic pyroxene granulites and syngranulite metasomatites (quartz blastomylonites with orthopyroxene, sillimanite, and garnet; veins and vein-like bodies of orthopyroxene–garnet and diopside–scapolite rocks) contain similar assemblages of syngenetic fluid inclusions (which are hosted mostly in quartz and also in garnet, orthopyroxene, and scapolite) of contrasting chemical composition: nearly pure СО2 (distinctly predominant), brines (the dominant salts are CaCl2 and NaCl), and N2 ± H2O. These three types of inclusions coexist in the same generations of early inclusions: rarer primary (p) and predominant primary–secondary (ps). The CO2 inclusions have either high or low densities, and the N2 inclusions are of low density. The brine inclusions show a wide range of total salt contents (up to 30–35 wt%) and variable concentration proportions of the dominant salts: p-inclusions with a salinity of 20 wt% CaCl2 + 10 wt% NaCl; ps-inclusions with a salinity of 5 wt% CaCl2 + 20 wt% NaCl; p- and ps-inclusions with a salinity of 5–23 wt% NaCl eq; and p-inclusions with halite (up to 35 wt% NaCl). In general, CaCl2 is the predominant salt component in the early p- and ps-inclusions of the rocks. Considered together, currently available data (including Sr, Nd, and O isotope systems) on these rocks indicate that the external fluid flow during the origin of granulites was evidently of mantle origin. At the peak P–T parameters, the inclusions were entrapped from a heterogeneous fluid in which immiscible water–salt and CO2-rich fluids, which initially contained N2, coexisted. Data on the chemical composition and salt concentrations of the fluids, $${{a}_{{{{{\text{H}}}_{2}}{\text{O}}}}}$$ = 0.40–0.51, are compared with the theoretically predicted phase state of the fluids and the properties of the coexisting immiscible fluid phases at the estimated P–T parameters of granulite petrogenesis on the basis of numerical models in the H2O–CO2–NaCl and H2O–CO2–CaCl2 ternary systems. The location of the tie-lines and solvus were calculated to subsequently use for the thermodynamic prediction. The paper discusses similarity and the reasons for the difference between the theoretical compositions of the generated fluid phases and the composition of fluid inclusions, geochemical consequences of the heterogenization of granulite fluids (the formation of concentrated alkaline brines and a potentially acidic CO2-rich fluid phase, the values of the mass and volume fractions of these phases depending on variations in the composition of the initial homogeneous fluid, etc.). It follows that an extensive region of the compositions of aqueous fluids with different concentrations of CO2 and Na and Ca chlorides exists at the P–T parameters of HP granulites in which originally homogeneous fluid splits into compositionally contrasting fluid phases with different properties. This region of coexisting immiscible fluids significantly expands with increasing CaCl2 concentration. Hence, the lower crust at the level of the HP granulite facies may be the region where high-temperature immiscible fluids are generated. One of these fluids is a denser phase of alkaline brines, and the other is a less dense potentially acidic phase of H2O–CO2 fluids rich in CO2. Ascending along regional permeable zones, these fluid phases of deep origin can play an important role in magmatic, metamorphic, metasomatic, and ore-forming processes in the middle and upper crust.

For the first time, the isotopic composition of oxygen, the content of trace elements, and the U–Pb zircon age were determined for kyanite–gedrite metasomatites from the Dyadina Gora ore occurrence, Belomorian Mobile Belt, Fennoscandian Shield. The zircon cores preserved from the protolith are characterized by a magmatic REE distribution and an average value of δ 18 O of about 3.0‰, and their age is close to 2400 Ma. The inner zones around the cores and rims of zircon were formed during metasomatic processes at the time of the Svecofennian metamorphism about 1870–1880 Ma ago, experienced strong fluid reworking, and are characterized by a decreased δ 18 O value to –0.9‰.

One unsolved problem of Archean metallogeny of the Russian part of the Fennoscandian Shield is related to the period of formation of orogenic gold deposits, the age of which was previously considered Early Proterozoic. Comprehensive studies identified the complex evolution of ores from the Novye Peski deposit and the first Neoarchean Sm–Nd isochron isotopic age (2583 ± 16 Ma) of the formation of orogenic gold of the Karelian Craton. A significant positive ε Nd( t ) value of +4.7 of gold-bearing metasomatites probably points to the link between the ore-forming fluid and the deep mantle source.

Manifestations of the main types of metasomatites (beresite, propylite, listwaenite, aceite, and gumbeite) were identified in the shear zones of the Fenno-Karelian craton on the basis of the previously proposed systematics of metasomatic facies. These metasomatites were formed in shear stress environments, which determined their morphological features, in particular, finely banded texture. Comparatively low-temperature conditions of infiltration process and salting out effect (reduction of CO2 solubility with increasing salt content) lead to the heterogenization of fluid into two phases: aqueous salt solution and almost pure CO2. This results in more aggressive and mobile behavior of the fluid, and, correspondingly, more intense differentiation of the matter and contrast in metasomatic banding. Relations between metasomatic parageneses indicate an evolution trend of the processes from propylite, beresite and listwaenite to alkaline varieties and their repeated manifestation in the same shear zones. The results of Rb-Sr isochron dating of ore metasomatites from eight deposits and occurrences of the Fenno-Karelian craton (more than 100 samples of rocks and minerals) confirm previous assumptions. In general obtained data show that the shear zones controlling the distribution of the studied occurrences operated as fluid pathways during a long time period, up to 200 Ma, after the Svecofennian orogeny completion and did not show any correlation with Paleoproterozoic and Neoarchean magmatism. Rb-Sr isotope data on the metasomatites indicate three peaks of the post-Svecofennian metallogenic activity: 1700–1780, 1600–1650, and 1400–1500 Ma. Since the studied ore deposits were formed within tectonic structures, which evolved on the Archean crust and have a long prehistory, and fluid flows were subjected to intensive contamination by ancient crustal material, a relatively high initial Sr isotope ratios of formed ore-metasomatic systems were developed. High variablity of this value in the studied rocks ((87Sr/86Sr)0 from 0.706 to 0.750) is related to the heterogeneity of crustal protolith and to the relative storage and manifestation of the juvenile component of the fluid, which was responsible for the metasomatic transformation of the Archean and Paleoproterozoic rocks and ore-deposit formation.

The Sm-Nd isotope-chronological method is used for the first time to investigate the whole rock and rock-forming minerals from metasomatic sillimanite orthopyroxene rocks in the Por'ya Guba nappe of the Lapland granulite belt. As a result isochrone values of the age are obtained, which allows estimate the minimum time intervals that have passed from the moment of formation of the investigated rocks. They indicate that peak conditions of collision metamorphism in fluid-permeable shear zones of the LGB occurred in the Paleoproterozoic Svekofennian age when high-temperature high-pressure sillimanite-orthopyroxene metasomatic rocks were formed. The obtained data make it possible to assume that, with regard to the measurement errors, high-pressure metasomatism did not last over 10 Ma, and this process did not coincide in time with older medium pressure metamorphism.

This study presents the first U/Pb SHRIMP II dates on zircons from metasomatic sillimanitehypersthene rocks within the Porya Guba nappe of the Lapland Granulite Belt. The results yielded a Paleoproterozoic Svecofennian age (1913–1914 Ma) of the HT/HP metasomatism in shear zones during collision-related metamorphic events in the Lapland Granulite Belt.