Diamonds were lately identified in chromitites from ophiolites and in volcanic rocks. Although the tectonic settings of diamonds found in these rocks are different, the diamonds are identical in small size, cuboctahedral habit, sets of minor admixture elements, and isotopic characteristics. A model is suggested for their formation during various stages of a single evolutionary cycle of the oceanic lithosphere, in relation to the geochemical and dynamic features of an ascending flow of mantle material, which produces the oceanic lithosphere at mid-oceanic ridges. In contrast to the continental lithosphere, in which mantle diamonds are usually related to kimberlite and lamproite magmatism in the presence of abundant CO2-rich fluid, diamonds in the oceanic lithosphere crystallize in environments poor in fluid and containing carbon mostly in its reduced forms. In the asthenospheric part of the ascending flow, carbon may occur in the form of nanometer-sized diamonds. In the upper parts of the oceanic lithosphere, the diamonds are overgrown and become microdiamonds (0.2–0.7 mm) within chromitites. After basaltic magma is derived from pyrolite, the residual harzburgites with lenses of diamondiferous chromitites are brought (at spreading) to the convergent boundaries of oceanic lithospheric plates, where the following two processes can proceed. If the oceanic lithosphere collides with a continental plate, the obducted material of the oceanic lithosphere is transferred to the surface of the continental margin and forms ophiolite massifs hosting diamond-bearing chromitites. If the oceanic lithosphere is subducted, the residual peridotite already enriched in volatiles is remelted. The arc magmas thus derived host diamond microcrystals, which have been formed in the chromitites and are sometimes found in volcanic lavas and ashes.

The model of the formation of the Earth–Moon system during the compression and fragmentation of a gas–dust cloud (Galimov, 2011; Galimov and Krivtsov, 2012) suggests an unusual mechanism for the formation of the Earth’s core. In particular, the model predicts that iron in the Earth’s core should be enriched in the light isotope, and the Earth’s mantle should be, conversely, enriched in the heavy isotope compared to the primary iron (of chondrites). The alternative (megaimpact) model does not allow for this phenomenon. This problem could be solved by comparing the iron isotope composition of the Earth’s and Moon’s mantles. The best representation of the iron isotope composition of the lunar mantle (δ57Fe) is given by the Fe isotope composition of lunar basalts with very low titanium content (VLT), just as the best representation of the isotope composition of iron in the Earth’s mantle is given by the δ57Fe of the Earth’s mid-oceanic ridge basalts (MORB). VLT basalts are relatively scarce on the lunar surface, unlike high-titanium basalts, which fill lunar lowlands. Their iron isotope composition has not yet been measured. We were the first to analyze the iron isotope composition of very low-titanium lunar basalts (VLT) in material delivered by the Luna 24 space mission. Our data indicate that the δ57Fe of Earth’s mantle is higher than the δ57Fe of the bulk silicate Moon, which means (with a high degree of probability) that the Earth’s core is enriched in the light iron isotope. This, in turn, is in good agreement with the model of formation of the Earth–Moon system by the compression and fragmentation of the gas–dust cloud.

—We have studied volcanogenic diamonds in the context of a discussion of their genesis, including some assumption on their artificial origin. The carbon isotope composition of diamonds collected from the eruption products of Tolbachik volcano (δ13CVPDB from –22 to –29‰) is within the range of the δ13CVPDB values of natural diamonds, including those from kimberlites. The δ15NAir values of the Tolbachik diamonds, measured for the first time (–2.58 and –2.32‰), correspond to δ15NAir of volcanic gases and differ from that of atmospheric nitrogen (δ15NAir = 0‰), which may be expected in synthetic diamonds. In the studied volcanogenic diamonds, as in synthetic ones, the nitrogen impurity is unaggregated. However, such an unaggregated form of nitrogen is specific to many natural diamonds (e.g., variety II diamonds, according to Orlov’s classification). Impurity elements (Cl, F, O, S, Si, Al, Ca, and Na) are locally concentrated in volcanogenic diamonds; they are a constituent of micro- and nanoinclusions in them. The high contents of F and Cl in the studied diamonds are correlated with the composition of volcanic gases; there is no reason to expect a similar correlation in synthetic diamonds. Moreover, the studied cube-octahedral Tolbachik diamonds have a number of accessory forms, some of which are not observed in synthetic diamonds. Their surfaces are frequently covered with films composed of Mg–Fe and Ca–Mg silicates, aluminosilicates, sulfates, metal alloys, and native Al. Mineral inclusions in the studied diamonds are Mn–Ni–Si alloys and silicides varying in composition from (Mn,Ni)4Si to (Mn,Ni)5Si2, Mn5Si2, and pure Mn silicide MnSi. Summing up the obtained data, we conclude that volcanogenic diamonds form in a strongly reducing environment, in which silicides and native metals and their alloys are stable. The predominant cube-octahedral morphology of these diamonds and the unaggregated nitrogen impurity point to their short-term residence under high-temperature conditions. This makes them similar, to some extent, to synthetic diamonds. There are, however, clear differences as well. Volcanogenic diamonds are similar in compositional peculiarities, including isotope compositions, to natural diamonds that form under most unfavorable conditions, such as cuboids, balases, carbonado, and some diamonds of the eclogite paragenesis. They also resemble diamonds found in situ in harzburgite and chromitite of ophiolites. This suggests a specific mechanism of formation of both volcanogenic and ophiolitic diamonds in the oceanic lithosphere.

We carried out a numerical study of the appearance of a shock wave during the collapse of a bubble in a hydrocarbon aqueous solution. The conditions for the appearance of a shock wave are obtained depending on the solute, the concentration of the solution, and the temperature. This work was carried out as part of the development of a method for producing diamonds upon cavitation in carbon-containing liquids.

This article discusses some features of geochemistry of the Earth and the Moon, which manifests the specificity of the mechanism of their formation by fragmentation of protoplanetary gas-dust condensation (Galimov & Krivtsov, 2012). The principal difference between this model and other hypotheses of the Earth-Moon system formation, including the megaimpact hypothesis, is that it assumes the existence of a long stage of the dispersed state of matter, starting with the formation of protoplanetary gas-dust condensation, its compression and fragmentation and ending with the final accretion to the formed high-temperature embryos of the Earth and the Moon. The presence of the dispersed state allows a certain way to interpret the observed properties of the Earth-Moon system. Partial evaporation of solid particles due to adiabatic heating of the compressing condensation leads to the loss of volatiles including FeO. Computer simulations show that the final accretion is mainly performed on a larger fragment (the Earth’s embryo) and only slightly increases the mass of the smaller fragment (the Moon embryo).This explains the relative depletion of the Moon in iron and volatile and the increased concentration of refractory components compared to the Earth. The reversible nature of evaporation into the dispersed space, in contrast to the kinetic regime, and the removal of volatiles in the hydrodynamic flow beyond the gas-dust condensation determines the loss of volatiles without the effect of isotopes fractionation. The reversible nature of volatile evaporation also provides, in contrast to the kinetic regime, the preservation of part of the high-volatile components, such as water, in the planetary body, including the Moon. It follows from the essence of the model that at least a significant part of the Earth’s core is formed not by segregation of iron in the silicate-metal melt, but by evaporation and reduction of FeO in a dispersed medium, followed by deposition of clusters of elemental iron to the center of mass. This mechanism of formation of the core explains the observed excess of siderophilic elements in the Earth’s mantle. It also provides a plausible explanation for the observed character of iron isotopes fractionation (in terms of δ57Fe‰) on Earth and on the Moon. It solves the problem of the formation of iron core from initially oxide (FeO) form. The dispersed state of the substance during the period of accretion suggests that the loss of volatiles occurred during the time of accretion. Using the fact that isotopic systems: U–Pb, Rb–Sr, 129J–129Xe, 244Pu–136Xe, contain volatile components, it is possible to estimate the chronology of events in the evolution of the protoplanetary state. As a result, agreed estimates of the time of fragmentation of the primary protoplanetary condensation and formation of the embryos of the Earth and the Moon are obtained: from 10 to 40 million years, and the time of completion of the earth’s accretion and its birth as a planetary body: 110 – 130 million years after the emergence of the solar system. The presented interpretation is consistent with the fact that solid minerals on the Moon have already appeared at least 60 million years after the birth of the solar system (Barboni et al., 2017), and the metal core in the Earth and in the Moon could not have formed before 50 million years from the start of the solar system, as follows from the analysis of the Hf-W system (Kleine et al., 2009). It is shown that the hypothesis of megaimpact does not satisfy many constraints and does not create a basis for the explanation of the geochemistry of the Earth and the Moon.

The fluid composition varies between three end-members: carbonatitic melts, rich in carbonate, Ca, Fe, Mg, K and P; Hydrous-silicic melts, rich in Si, water, Al and K and brine rich in water, Cl and K.Here we report new data from micro-inclusion bearing diamonds from Brazil.The micro-inclusions contain melts that span the range between carbonatitic and hydro-silicic compositions.The entire range between the two end members is observed in single diamonds.Thus, in two diamonds, it is possible to follow the evolution of the melt during diamond growth.

Substantial role of fluids in processes of diamonds formation was first emphasized by Zezin et al. (1981) and Galimov (1984) from the INAA study of diamonds from Russian deposits.Importance of fluids for diamond origin is confirmed in the present study.In this report we present results of the instrumental neutron activation analyses (INAA) of individual diamond crystals from Venezuela placers and from several pipes of the Arkhangelsk region (NE Europe).Samples from Arkhangelsk region are presented by chips left after inclusions recovery and represent both parageneseses.The data on the composition of mineral inclusions is published elsewhere (Zakharchenko et al., 1991) The parageneses of the Venezuelan diamonds is unknown, however, the absolute predominance of basic inclusions (more than 98%, N.V. Sobolev et al., 1997, submitted) in diamonds from these placers permits to attribute these samples to E-type.All samples were examined under optical microscope with crossed and parallel polarizers.The magnification used was 50x-500x.No inclusions were detected in analyzed samples under these conditions.The samples were individually boiled in Teflon beakers in mixture of pure acids (HF+HNO3) and rinsed in distilled water before and after irradiation.Integral flux was about 8xl017 neutrons.KH1 and RUS1 were used as standards and as flux monitors.Samples were counted with a HpGe detector in three periods.The concentration of the following elements were determined by INAA: La, Ce, Sm, Eu, Tb, Yb, Lu, Ca, Sr, Ba, K, Sc, Cr, Fe, Co, Ni, Rb, Na, As, Hf, Zr, Th, U, Ta, Se, Zn, Au, W. Low concentration of impurities and small mass of the samples lead to relatively high errors (up to 50 rel% at 3a) for some elements; for majority the errors were less than 20 rel%.In order to detect surface contamination (if any) by samples preparation, we analyzed (111) surfaces of several diamonds prior and after cleaning procedure by the Rutherford Backscattering (Shiryaev and Kulikauskas, in prep.).It was shown that our treatment introduced small amount of Au.As it is impossible to correct rigorously the INAA figures for gold (1-10 ppb), Au is not discussed further.Trace elements determined in diamonds may be attributed to structural impurities or to micro¬ inclusions.As is known, N, H, Ni and B could present as substitutional or interstitial atoms in natural and synthetic stones.Arsenic and phosphorus could be incorporated as substitutional atoms during HPHT synthesis.The presence of structural oxygen, sulfur in natural lb diamonds and Co in synthetic stones was inferred from EPR and luminescence data but these interpretations are not decisive.From results of nuclear probing, IR studies and crushing of diamonds it was suggested (Melton and Giardini, 1981; Navon et al., 1988; Properties of diamond, 1992;Bulanova et al., 1993) that all diamonds contain homogeneously distributed submicroscopic inclusions of a parental magma, consisting of a silicate melt with a miscible carbonate and immiscible sulfide fractions together with volatiles (H20, C02, CO, CH4).It is shown that if diamond contains mineral inclusion the output of gases will be higher.The volatiles not related to mineral inclusions may reside in micro cavities.The results of positron annihilation (PAS) studies by Fujii et al. (1995) and our PAS and Small-Angle X-ray Scattering (Shiryaev et al., in prep.)investigations of diamonds of different types in Robertson's classification, clearly point to the existence of voids with sizes ranging approximately from 10 to 25 A and filled with a low-electron density material.From PAS it follows that pressure in this inclusions exceeds 1 GPa.These inclusions could serve as a host for entrapped fluids.

The results of the computer simulation for the circumsolar gas-dust cloud evolution are presented. The particle dynamics method is used. We show that gas-dust clusters can be formed in ring-shaped structures of protoplanetary disks. It is demonstrated that the clusters are formed as a result of the counteracting of the self-gravitational force of the ring and the gravity of the Sun. This process has a probabilistic nature. The range of the system parameters providing the clusters formation is obtained. Different scenarios of the ring evolution are observed and analyzed. The considered gas-dust clusters can be precursors for the further formation of the planet-satellite systems.

It was shown that the history of the biosphere is closely related to processes caused by low solar luminosity. Solar radiation is insufficient to maintain the Earth's surface temperature above the freezing point of water. Positive temperatures are kept owing to the presence of greenhouse gases in the atmosphere: CO2, CH4, and others. Certain stages in the development of the biosphere and climate are related to these effects. Methane was the main carbon-bearing gas in the primordial atmosphere. It compensated the low solar luminosity. Life originated under the reduced conditions of the early Earth. Methane-producing biota was formed. Methane remained to be the main greenhouse gas in the Archean. The release of molecular oxygen into the atmosphere 2.4 Ga ago resulted in the disruption of the established mechanism of the compensation of the low solar luminosity. Methane ceased to cause a significant greenhouse effect, and the content of carbon dioxide was insufficient to play this role. A global glaciation began and had lasted for approximately 200 million years. However, the increasing CO2 content in the atmosphere reached eventually a level sufficient for the compensation for the low solar luminosity. The glaciation period came to an end. Simultaneously, a conflict arose between the role of CO2 as a gas controlling the thermal regime of the planet and as an initial material for biota production. As long as the resource of biotic carbon was inferior to that of atmospheric CO2, the uptake of atmospheric CO2 related to sporadic increases in biologic production was insufficient for a significant change in the thermal regime. This was the reason for a long-term climate stabilization for 1.5 billion years. By 0.8 Ga, the resource of oceanic biota reached the level at which variations in the uptake of atmospheric CO2 related to variations in the production of organic and carbonate carbon became comparable with the resource of atmospheric CO2. Since then, an oscillatory equilibrium has been established between the intensity of biota development and climate-controlling CO2 content in the atmosphere. Glaciation and warming periods have alternated. These changes were triggered by various geologic events: intensification or attenuation of volcanism; growth, breakup, or migration of continents; large-scale magmatism; etc. A new relation between atmospheric CO2 and biotic carbon was established in response to the emergence of terrestrial biota and the appearance of massive buffers of organic carbon on land. The interrelation of the biosphere and climate changed.

Data on the diamond synthesis in experiments with carbon-saturated metal melts at moderate pressures and temperatures are presented. Features of the resulting diamond phase, the types and nature of inclusions are discussed and compared with those for natural microdiamonds found at the volcanic rocks of Kamchatka.

МИКРОКРИСТАЛЛИЧЕСКИЕ АЛМАЗЫ В ОКЕАНИЧЕСКОЙ ЛИТОСФЕРЕ И ИХ ВОЗМОЖНАЯ ПРИРОДА

The origin of diamonds in the lava and ash of the recent Tolbachik eruption of 2012–2013 (Kamchatka) is enigmatic. The mineralogy of the host rocks provides no evidence for the existence of the high pressure that is necessary for diamond formation. The analysis of carbon isotope systematics showed a similarity between the diamonds and dispersed carbon from the Tolbachik lava, which could serve as a primary material for diamond synthesis. There are grounds to believe that the formation of Tolbachik diamonds was related to fluid dynamics. Based on the obtained results, it was suggested that Tolbachik microdiamonds were formed as a result of cavitation during the rapid movement of volcanic fluid. The possibility of cavitation-induced diamond formation was previously theoretically substantiated by us and confirmed experimentally. During cavitation, ultrahigh pressure is generated locally (in collapsing bubbles), while the external pressure is not critical for diamond synthesis. The conditions of the occurrence of cavitation are rather common in geologic processes. Therefore, microdiamonds of such an origin may be much more abundant in nature than was supposed previously.

Происхождение алмазов, найденных в лаве и пепле недавнего извержения (2012–2013 гг.) вулкана Толбачик на Камчатке, загадочно. В минеральном составе вмещающих пород нет никаких признаков существования высокого давления, которое необходимо для образования алмазов. Мы изучили изотопный состав углерода алмазов и дисперсного углерода в лаве Толбачика, который мог служить субстратом для синтеза алмазов, и установили, что они схожи. Есть свидетельства того, что формирование алмазов Толбачика связано с динамикой флюида. На основании полученных результатов предполагается, что микроалмазы Толбачика образовались в процессе кавитации, возникшем при быстром движении вулканического флюида. Ранее нами была показана теоретическая возможность образования алмазов в процессе кавитации, и эта гипотеза была подтверждена экспериментально. Ультравысокое давление при кавитации создается в локальных точках (схлопывающиеся пузырьки); при этом давление окружающей среды не является определяющим для синтеза алмаза. Условия возникновения кавитации достаточно обычны в геологических процессах. Поэтому микроалмазы подобного происхождения могут быть распространены в природе гораздо шире, чем это предполагалось ранее.

We consider features of the carbon composite nano-particles formation at cavitation by means of the hydro impact. The comparison of given method with existing methods of synthesis in nanotechnology was carried out. The crystal structure of the various carbon nanoforms synthesized by hydrodynamic cavitation in a mixture of water and isopropyl alcohol was investigated using the methods of electron diffraction. Such polymorphs of carbon as the nano-diamond, nanographite and composites were revealed. The lattices characteristics of the synthesized carbon nano forms were analyzed. Applications of results for microelectronics were considered.

The carbon isotope composition of microdiamonds found in products of the Tolbachik Volcano eruption, Kamchatka (porous lavas and ash), was studied. The isotope composition of microdiamonds (with an average value of δ 13 C =–25.05‰) is close to that of microsized carbon particles in lavas (from–28.9 to–25.3‰). The general peculiarities of the diamond-forming environment include (1) no evidence for high pressure in the medium; (2) a reduced environment; and (3) mineralogical evidence for the presence of a fluid. The geochemical data characterizing the type of diamonds studied allow us to suggest that they were formed in accordance with the mechanism of diamond synthesis during cavitation in a rapidly migrating fluid, which was suggested by E.M. Galimov.