Based on the mean contents of elements and their standard deviations estimated in the first part of this contribution (Naumov et al., 2023), we compared in detail the geodynamic settings distinguished earlier. In order to compare the compositions of mafic melts, a correction was introduced for changes related to the fractionation of the main minerals. Using numerical criteria, the elements were arranged in a sequence of the increasing degree of compatibility during melting and crystallization, and regular variations in element contents normalized to the mean composition of oceanic-island melts were distinguished. The melts of mid-oceanic ridges show a monotonous increase in normalized contents from the most incompatible (Cs, Ba, U, La, etc.) to compatible elements (Sc, Ni, and Cr). The settings of convergent plate boundaries show relative enrichment in the most incompatible elements and significant negative Ta−Nb anomalies relative to neighboring elements. The magmas of continental rifts show the most significant enrichment in the most incompatible elements, as well as Pb, Li, and some other elements. Indicator element ratios showing significant variations between the settings were distinguished for mafic melts. Some element ratios are almost identical (within observed variations) in mafic melts from all the settings. The mean element ratios in mafic, intermediate, and silicic magmas show three types of behavior. Some ratios (including the canonic ratios Nb/Ta, Zr/Hf, etc.) in intermediate and silicic magmas are inherited from the composition of mafic melts. Some ratios show irregular changes from mafic to silicic melts (Sr/Cr, F/Th, etc.). Some other ratios change monotonously and significantly in the sequence from mafic to silicic melts (Ni/Yb, Lu/P, etc.). The variations in element ratios are related to the crystallization differentiation of melts and contributions of geochemically contrasting reservoirs.

Data from our original database, which includes more than 2 600 000 analyses for 75 elements of mineral-hosted melt inclusions and quench glasses in volcanic rocks, are generalized to calculate the mean concentrations of major, volatile, ore, and trace elements in magmatic melts from the following dominant geodynamic environments: (I) spreading zones of oceanic plates (mid-oceanic ridges), (II) environments affected by mantle plumes in oceanic plates (oceanic islands and lava plateaus), (III, IV) environments related to subduction processes (III is zones of arc magmatism on the oceanic crust, and IV is zones of magmatism in active continental margins in which magma-generating processes involve the continental crust), (V) environments of continental rifts and areas with continental hotspots, and (VI) environments of backarc spreading. A histogram of SiO2 distribution in natural magmatic melts shows a bimodal distribution: one of the maxima falls onto SiO2 concentrations of 50–52 wt

Data from our original database, which includes more than 2 600 000 analyses for 75 elements of mineral-hosted melt inclusions and quench glasses in volcanic rocks, are generalized to calculate the mean concentrations of major, volatile, ore, and trace elements in magmatic melts from the following dominant geodynamic environments: (I) spreading zones of oceanic plates (mid-oceanic ridges), (II) environments affected by mantle plumes in oceanic plates (oceanic islands and lava plateaus), (III, IV) environments related to subduction processes (III is zones of arc magmatism on the oceanic crust, and IV is zones of magmatism in active continental margins in which magma-generating processes involve the continental crust), (V) environments of continental rifts and areas with continental hotspots, and (VI) environments of backarc spreading. A histogram of SiO2 distribution in natural magmatic melts shows a bimodal distribution: one of the maxima falls onto SiO2 concentrations of 50–52 wt % and the other onto 72–76 wt %. The most widely spread melts contain 62–66 wt % SiO2. Mean temperatures and pressures are calculated for each of the environments. The normalized multielemental patterns presented for environments I through VI show the ratios of the mean concentrations of elements in magmatic melts of mafic, intermediate, and felsic composition to the concentrations in the primitive mantle. Mean ratios of incompatible, trace, and volatile components (H2O/Ce, K2O/Cl, Nb/U, Ba/Rb, Ce/Pb, etc.) are evaluated for the melts of each of the environments. The variations in these ratios are calculated, and it is demonstrated that the ratios of incompatible elements are mostly statistically significantly different in the different environments. The differences are particularly significant between the ratios of the most differently incompatible elements (e.g., Nb/Yb) and some ratios involving volatile components (e.g., K2O/H2O).

The paper considers the geochemical effects of impact processing of the polar regolith of the Moon. It contains an admixture of water ice, which can (should?) provide conditions for possible chemical reactions. To date, only one geochemical effect was reliably found—the formation of hematite Fe 2 O 3 , which is uncharacteristic for relatively low selenographic latitudes. In the work, a thermodynamic analysis of the conditions required for the formation of hematite is carried out. It is shown that this requires the presence of free oxygen, which (this is a possible option) can accumulate during the dissipation into outer space of hydrogen formed during water decomposition. The specific process or processes of hematite formation require further study. It is very likely that impact processing of polar regolith also leads to hydration of silicate glasses and to the formation of heavy hydrocarbons. The dissipation of free hydrogen into outer space, which, apparently, is formed in these processes, should lead to an increase in the deuterium content in the remaining hydrogen. The Н 2 О ice of the polar regolith likely contains a significant amount of heavy water. Future investigations in the polar regions of the Moon, especially with the delivery of samples to Earth, should confirm or refute these conclusions and assumptions.

-The brief review summarizes data on the chemical and mineral composition, as well as on the physical properties, of the first extrasolar comet 2I/Borisov, obtained from observations that were carried out from September 2019 to the end of March 2020. It is noted that the qualitative chemical composition of the volatile and mineral components comet 2I/Borisov is similar to the composition of comets in the Solar System, but there are differences that indicate the specific conditions for the formation of its nucleus in a circumstellar gas and dust disk. Different release rates of CO and H2O molecules in the vicinity of perihelion indicate the possible heterogeneity of the comet's nucleus, which was formed from more homogeneous ice blocks, but differing in composition. These constituent blocks could have formed over a wide range of radial distances: from the snow line of H2O to the CO snow line. Their accumulation in the comet's nucleus indicates large-scale mixing of protocometary bodies in the circumstellar disk. No spectra of finely crystalline magnesium silicates were found in cometary coma of 2I/Borisov, which can be interpreted as the absence of a significant amount of gas and dust transfer from the inner hot regions of the disk to the outside, into the zone of formation of protocometary bodies.

In the second part of this study, we analyze how crystallization differentiation can affect concentrations of elements and their ratios in melt inclusions and glasses of rocks in major geodynamic environments. The paper presents analysis of experimental data on the partition coefficient of elements between minerals (olivine, pyroxenes, garnet, amphibole, biotite, sulfide, apatite, spinel, ilmenite, rutile, and zircon) and silicate melts, which were discussed in the first part of this study. It is demonstrated that the crystallization of major minerals only insignificantly affects the ratios of incompatible elements. The partition coefficients of some elements between accessory minerals and melts can be very high, but the effects of crystallization differentiation cannot be significant because of the small amounts of the crystallizing phases. These effects are the most significant for chalcophile elements (Cu, Ni, and others), at the separation of sulfides, and for Nb and Ta, at the crystallization of rutile. Differences in concentrations of various elements and their ratios to Cs concentrations are discussed with reference to various geodynamic environments. The maximum values of the ratios of practically all elements to Cs were found in melts in mid-oceanic ridges. The melts of oceanic islands and backarc basins are characterized by relatively low ratios, without any significant anomalies. The lowest ratios of elements to Cs were found in melts of continental and marginal environments. These melts are also characterized by clearly seen geochemical anomalies that are typical of rocks of the corresponding environments (negative Ta–Nb, positive Pb, and other anomalies).

The paper estimates the minimum, mean and maximum thickness of regolith and degree of its impact-caused reworking as a function of depth based on spatial density of small impact craters for the floors of polar craters Shoemaker, Sverdrup and Shackleton and for the landing sites of Luna-16, -17, and -24. Key parameter for these calculations is Dcr, the boundary diameter between the equilibrium and non-equilibrium parts of crater population. It was found to be 80 m for the Luna-24 site and crater Shackleton, 100 m for the Luna-16 and -17 sites, 350 m for crater Sverdrup and 1000 m for crater Shoemaker. The median thicknesses of regolith for these areas were found to be 3,2, 4, 14, and 40 m, respectively. For these areas, the number of the reworking events was found to be 1, 6, 2, 7, and 20 for the 2 m depth, 3, 4, 14 and 40 times for the 1 m depth, 6, 8, 28 and 80 times for the 0,5 m depth, 16, 20, 70, and 200 times for the 0.2 m depth, and 64, 80, 280, and 800 times for the 0.05 m depth. These reworking impacts should mechanically mix the polar regolith and cause multiple local vaporization / condensation of the frozen volatiles leading to their physico-chemical differentiation.

Published data on the composition of mineral-hosted inclusions and quenched glasses of rocks were used to estimate the mean concentrations of 45 volatile, trace, and ore elements in silicate igneous melts from the main geodynamic settings of the Earth and in natural fluids. The following geodynamic settings were distinguished according to the conditions of formation and evolution of the igneous melts: (I) oceanic spreading zones (mid-oceanic ridges), (II) oceanic mantle-plume zones (oceanic islands and lava plateaus); (III and IV) subduction-related settings (III is island-arc zones, and IV is active continental margins); (V) continental rifts and hotspot zones; and (VI) backarc spreading basins related to subduction. The contents of the elements in basic and felsic melts were compared in settings III, IV and V. It was shown that differences in the enrichment factors of ore elements between the geodynamic settings could be caused by variations in the contribution of fluids to element transport and accumulation. Ratios of element contents in each of the geodynamic environments to the global mean values were calculated.

In this paper, we summarize the experimental data on the features of the mineral, chemical, and isotopic compositions of minor bodies of the Solar System—asteroids, Saturn’s satellites, and nuclei of comets of different dynamic types—which suggest that the formation of these bodies was significantly influenced by the mixing of different-genesis matter: presolar and nebular. The latter was formed in the circumsolar gas–dust protoplanetary accretion disk that is also called the nebula. The matter of presolar origin includes amorphous iron–magnesium silicates, refractory organic compounds, volatile organic compounds, amorphous water ice, as well as ices of СО 2 , NH 3 , CH 3 OH, CO, etc. The species of nebular origin are aluminum-, calcium-, and titanium-rich refractory inclusions (known as CAls), microcrystalline magnesium silicates, as well as crystalline water ice, the hydrogen isotopic composition of which is several times lower than that of water ice of the protosolar nebula. The presolar- and nebular-origin matter could be mixed because, in the circumsolar disk at the early stages of its evolution, in addition to the main accretion flux of the gas–dust matter passing through the disk toward the Sun, there was a flux moving in the opposite direction, from the Sun, from the inner hot regions of the circumsolar disk outward to its external regions. There, the nebular matter was mixed with the protosolar matter, which had been precipitating onto the disk from its accretion envelope, mainly onto its edge, during the first million years of its evolution. The currently available package of the experimental data allows us to suppose that it is exactly the mixing of the matter from two regions of the circumsolar disk, within which the P–T conditions significantly differed, that may explain the presence of chemically and isotopically heterogeneous ice–rock bodies in the outer Solar System.

The paper summarizes data on germanium and gallium concentrations in natural magmatic melts as follows from analyses of mineral-hosted inclusions and quench glasses in volcanic rocks. Germanium concentrations in melts vary from 0.96 to 17.6 ppm (1472 determinations). The geometric mean germanium concentration in silicate melts is 1.56 ppm, which is quite close to the clarke value. Concentrations of gallium in magmatic melts vary from 0.47 to 495 ppm (8755 determinations). The geometric mean of gallium concentration in silicate melts is 19.0 ppm, which is also close to the clarke value. Germanium concentration in hydrothermal fluids ranges from 0.01 to 930 ppm (405 determinations), and the geometric mean value is 17.0 ppm. Concentrations of gallium in fluids vary from 0.02 to 320 ppm (441 determinations), with a geometric mean of 2.0 ppm. The possible reasons for the differences in germanium and gallium concentrations in natural melts and fluids are discussed.

The mean concentrations of volatiles, major, and trace elements are estimated in the magmatic melts of Kamchatka based on an our database that includes analyses of melt inclusions and quenched glasses of rocks for 75 elements (the database comprised 1 900 000 analyses as of late 2018). The determined concentrations are compared with analogous characteristics of melts from island arcs and active continental margins. The distribution of SiO2 concentrations (more than 105 000 analyses) in natural magmatic melts from all geodynamic environments is obviously bimodal, with maxima at SiO2 = 50–52 and 72–76 wt %. The paper presents binary diagrams that show the concentrations of major, volatile, trace elements, and REE and diagrams of the normalized patterns average concentrations of elements in the magmatic melts. The diagrams show distinguishing features of the melts of Kamchatka, for example, the elevated Ba/Nb ratios of Kamchatka mafic melts compared to those of melts in other zones, which may reflect a high content of subduction-related material during the derivation of the Kamchatka melts, with their Th deficit controlled by specifics of the fluid regime.

The studies of the composition and structure of comet 67P/Churyumov–Gerasimenko—a short-period comet of Jupiter’s family—which was an object of the recent Rosetta–Philae space mission, yielded results unique in many respects, since it was the first time that a comet was investigated in situ for a long stretch of time under varying conditions of insolation and activity. Due to the landing of the Philae probe, the data on the composition of mineral and organic fractions sampled directly from the cometary nucleus were obtained. Measurements of the coma composition performed with the instruments onboard the Rosetta spacecraft in the early period of observations allowed the data on the composition of its extremally volatile components (N2 and Ar) to be acquired for the first time, while the analysis of the coma composition performed in the postperihelion period provided an adequate insight into the composition of the ice fraction of the cometary nucleus. In the review, along with consolidating the experimental data, we discuss their implications arising in the context of cosmogony and cosmochemistry.

Authors’ original continuously updated database, which currently comprises data from 22 300 publications on mineral-hosted fluid and melt inclusions, is used to generalize data on the physicochemical parameters of processes that produced fluorite and barite deposits. The paper presents data on the following parameters of the fluids: temperature, pressure, density, salinity, and gas composition. The average composition (Н2О, CO2, CH4, N2, H2S, and CnHm) of fluids at fluorite–barite deposits is calculated. The paper reports the average composition of major gas components (CO2, CH4, N2, and H2S) of natural fluids at these deposits on the basis of Raman spectroscopic analyses of individual inclusions. Average F, S, and Ba concentrations are calculated for silicate magmatic melts and natural mineral-forming fluids.

Using numerical models, we have studied what depth of the outer layer the comet nuclei are degassed to when they are in orbits whose perihelion is close to the Sun for tens of years. The problem is topical, because it helps to understand how much the experimentally obtained results on the composition of comet comas depend on how long the comet is in its present-day orbit and how adequately the data obtained reflect the composition of comet nuclei as a whole. The proposed approach, which is demonstrated using comet 67P/Churyumov-Gerasimenko as an example, is based on a 3D comet nucleus surface relief model and takes into account not only its orbital motion, but also its diurnal rotation. The propagation of heat in the nucleus subsurface layers is described by a 1D heat conduction equation for a porous rock-ice composition of matter. Based on this approach, we have derived the temperature distributions in the subsurface layers for several surface patches located in the Ma’at region in 20 revolutions around the Sun, ~130 years.

As a continuation of our previous study, we estimated the mean contents of volatile, major, and trace components in silicic (>66 wt % SiO2) magmatic melts from main terrestrial geodynamic settings on the basis of our database, which includes (as of middle 2017) more than 1 500 000 determination of 75 elements in melt inclusions and quench glasses from rocks. Among the geodynamic settings are those related to subduction processes (III, island-arc zones originated on oceanic crust and IV, magmatic zones of active continental margins, where continental crust is involved in magma formation) and intracontinent rift and continental hot-spot regions (V). For each geodynamic setting, we calculated the mean contents of elements with confidence limits separately for melt inclusions and groundmass glasses and for the entire data set. Systematic differences were found between the mean compositions of melt inclusions and groundmass glasses from these geodynamic settings. Primitive mantle normalized spider diagrams were constructed for all geodynamic settings. Some ratios of elements and volatile components (H2O/Ce, K2O/Cl, La/Yb, Nb/U, Ba/Rb, Ce/ Pb, etc.) in silicic and mafic melts were compared. Variations in the ratios of various elements to Th, which is one of the most incompatible elements in silicic and mafic melts, were discussed.