Natural sheet magnesium silicates are potential sources of divalent cations, which are necessary for the mineralization of CO2 in the carbonates. In order to study the influence of inorganic (HCO3−) and organic (oxalate and citrate) ligands on the kinetics of dissolution of talc and serpentine, experiments were performed in a flow-through reactor at 25°C. Dissolution rates of natural silicates r (mol cm−2 s−1) in solutions of various compositions were calculated at the stationary stage of dissolution after a rapid initial stage, which is characterized by the formation of a surface leached layer depleted in magnesium. The presence of ligands increases the dissolution rate of magnesium silicates due to the formation of surface complexes, which leads to separation of magnesium from the surface and transition into solution. Initial incongruent stage may be the most promising for the development of carbonation technologies, since the minimum removal of the network-forming elements prevents the undesirable formation of secondary minerals (for example, clays), which exclude divalent cations from the carbonation process and greatly reduce the permeability of rocks.
The analysis of the layer-by-layer dynamics of snow chemical parameters in one of the observation points in the Pechora-Ilych biosphere reserve (Yaksha village) in the winter period 2019–2020 was carried out. It is shown that the chemical composition of atmospheric precipitation is more affected by long-range transport of substances. The peculiarities of atmospheric circulation and the regions from which air masses are transferred determine the saturation of precipitation with certain chemical components. The calculation of the trajectories of reverse transport of air masses allowed us to show the regions where air masses can form that come to the research area, carry substances and potentially form the chemical composition of precipitation. It is shown that the calculation of trajectories allows us to estimate the regions that are sources of pollutants entering the atmosphere. In general, this method of studying the chemical composition of snow is very informative and allows you to better understand the factors of its formation.
Experimental data were analyzed on the partitioning of trace elements between minerals (olivine, orthopyroxene, clinopyroxene, and feldspars) and silicate melts. The data span over a wide range of conditions (from 1 atm to 10 GPa and ~1000–2000 °C) and compositions of melt (from ultrabasic to ultrasilicic) and minerals. The dependence of logarithms of partition coefficients (lnDi ) on conditions and compositions was approximated by linear functions of 1/T, P/T (P is pressure, and T is absolute temperature) and compositional parameters of mineral and melt. It was found that Di /Dj values for a number of element pairs are independent of experimental parameters and vary within narrow ranges. The coefficients of Di dependencies on conditions and compositions were estimated by minimization of quadratic deviations of model Di and Di /Dj values from experimental values. The obtained equations can be used to calculate Di values for a number of elements with an accuracy of approximately a factor of 1.2–2.0. The obtained values were applied as an example for a model of formation of mafic melts of mid-ocean ridges through melting of a peridotite source and crystallization of primary magmas under crustal conditions.
A petrogeochemical study of basalts (lithophile elements and Sr-Nd-Pb isotopes, compositions of liquidus olivine and spinel) from the transition zone of the Southwest Indian Ridge in the area of the Du Toit and Andrew Bain faults revealed significant differences in their composition. Within the rift valley adjacent to the faults, tholeiites enriched in Na and depleted in Fe (Na-TOR genetic type) are typical. Deep-type basalts (TOR-1) are present in the western side of the Andrew Bain Fault. The outpouring of these types of magmas reflects a possible change in geodynamic regime during this zone formation: from deeper and higher temperature melting to shallower ones (Sushchevskaya et al., 2022). Differences in the primary melts of tholeiites from the rift valley and the Andrew Bain Transform Fault are also traced in the liquidus olivine compositions. The rift valley olivines are similar to typical Na-TOR olivines with a Mg content of Fo88–87, low Ni and elevated Mn. On the contrary, tholeiite olivines of the Andrew Bain Fault are enriched in Ni and depleted in Mn, which may indicate pyroxenite included in the primary melt formation. This component is either oceanic lithosphere recycled through the deep mantle or fragments of previously formed oceanic crust, which are subsequently involved in melting during the spreading axes jumping. A similar process is typical for the region of the Bouvet Triple Junction, where a significant heterogeneity of the olivine composition in terms of trace-element contents was revealed. The isotope characteristics of the Andrew Bain Fault tholeiites differ in Pb and Sr radiogenic composition and are similar to those of enriched magmas from such Indian Ocean rises as Crozet, Marion and Bouvet, but not from the Konrad and Af. Nikitin Rises. The source of such tholeiite melts is close in composition to the model HIMU type (with high U/Pb), possibly with an admixture of mantle material with EMII characteristics (with elevated Rb/Sr).
Based on the mean contents of elements and their standard deviations estimated in the first part of this research project (Naumov et al, 2022), we compared in detail the distinguished geodynamic settings. In order to compare the compositions of mafic melts, a correction to take into account changes related to the fractionation of main minerals was introduced. The use of numerical criteria made it possible to determine the sequence of elements by the degree of coherence during melting and crystallization of the main magmatic melts. Within this sequence, a regular variation in elemental contents normalized to the average composition of oceanic island melts was established. The melts of mid-ocean ridges show a monotonous increase in normalized contents from the most incompatible (Cs, Ba, U, La, etc.) to compatible elements (Sc, Ni, 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 highest 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.). There are ratios that changes monotonously and significantly in the sequence from mafic to silicic melts (Ni/Yb, Lu/P, etc.). The variations of element ratios are related to the crystallization differentiation of melts and contributions of geochemically contrasting reservoirs.
