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The paper presents experimental data on the impact vaporization of serpentinite. The experiment was carried out on a two-stage light-gas gun at the Institute of Mechanics of the Moscow State ...University by shooting a copper impactor (~0.5 g) at a speed of ~6 km/s. The vaporized material in the form of a condensate film was analyzed on a scanning electron microscope. The analysis showed that the Mg/Si ratio in the condensate drastically decreased (by ~1.8 times) compared to the initial ratio in the serpentinite target. Thus, it is shown that the evaporation of the impact melt of a silicate target is selective: the vapor is enriched in relatively volatile SiO
2
, whereas relatively low-volatility MgO is more retained in the residual melt. Our data thus suggest that the shock-explosive bombardment during the accretion of the Earth may have shifted the compositions of rocks at the planet’s surface from ultramafic to more acid. An acid trend in rock silicity in the course of accretion is possible if the vaporized matter and/or condensate were accumulated on the surface of the growing planet.
Native cobalt was found in amphibolite of the Kola superdeep borehole (SG-3) from a depth of 9630 m by a complex of local analytical methods (analytical scanning electron microscopy, electron ...backscatter diffraction). The studied amphibolite is a fine-grained melanocratic rock composed mainly of magnesioferri- hornblende and containing accessory native metal, telluride, sulphotelluride, and sulphide (Au, Ag, Pd, Bi, Cu, Pb, Zn, Sb, and Fe) mineralization.It also includes the clinopyroxene xenoclast carrying a fundamentally different set of accessories—poor in sulphides and including native cobalt. The absence of significant impurities, including iron, in native cobalt and its belonging to the hexagonal α-modification was determined. It is shown, that the metallic cobalt particles exposed during ion polishing of a compact pyroxene matrix cannot be a contaminant, introduced into the sample during drilling and sample preparation. Cobalt, obviously, was formed not only before the stage of retrograde metamorphism and subsequent hydrothermal processing of the amphibolite containing it, but probably long before the formation of the sedimentary protolith of this rock. That is, native cobalt belongs to the early high-temperature mineral phases inherited from the older Proterozoic—Archean main volcanism, while the time of formation of this layer of amphibolites dates back to the age of 2.4 billion years—the Early Karelian era of the Proterozoic.
Palladium mineralization was registered in the Kola superdeep borehole (SG-3) for the first time in samples from deep horizons (in the fault zone at ~10 km). A proper palladium mineral (merenskyite) ...with the formula Pd
1.00
(Te
1.21
Bi
0.79
)
2.00
was detected using the analytical electron microscopy and EBSD methods. The unusually high content of bismuth in the discovered merenskyite crystal most likely indicates the lower temperatures of its formation from a bismuth-rich fluid. This is supported by numerous finds of associated bismuth minerals (native and intermetallic minerals, sulfides, tellurides, and sulfotellurides) as well. A close geochemical association of noble and rare elements was revealed in the composition of the rich and diverse ore mineralization in the samples studied. It can be argued that a new type of mineralization was discovered for the SG-3 rocks: noble metal (Au–Ag–Pd) rare-element (Bi–Te).
A high-calcium high-temperature condensate is detected in the Earth’s impact Lonar crater for the first time. Its finding confirms in practice the theoretical conclusions made earlier from the ...experimental results. The high-silica condensate found in the Lonar crater, which is similar to those ones in the Zhamanshin crater and in the lunar regolith, confirms the absence of a correlation between the compositions of the target and the impact condensates. The presence of high-temperature condensate glasses in ring structures may be one of the diagnostic criteria to differentiate between volcanogenic and impact formations.
For the first time, high-purity native cobalt was detected in two preparations from a lunar regolith sample delivered by the Luna 24 automatic station. Presumably, it was formed during the ...condensation of a substance from an impact gas-plasma cloud. Previously, native cobalt of similar purity was observed only in products of low-temperature hydrothermal alteration of hyperbasites.
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A comparative study of impact glasses from the Lonar crater, located on the Deccan basalt plateau, India, and impact glasses from lunar regolith delivered by the Soviet automatic stations (AS)
...Luna-16
and
Luna-24
(Sea of Plenty and Sea of Crises) was carried out. Numerous natural alloys (Cu
3
Ni
2
, Ni
2
Cu and Ni
3
Cu) that were previously unknown in nature were discovered in the impactites of the Lonar crater and the regolith of the Moon. The discovery of such alloys expands the area of isomorphism in the Cu–Ni system. As a result of a comparison of impactites of the Earth and the Moon, similarities were discovered in the composition, size and morphology of particles of copper–nickel alloys, which may be an indicator of impact processes. One of the possible mechanisms for the formation of Ni–Cu particles was condensation from a gas–plasma cloud. A possible source of material for Cu–Ni alloys was both the impactor material and the target material.
For the first time, a high-temperature condensate in the form of two-component glass beads of about 200–400 nm size, consisting of an Al–Ca oxide core rimmed by a uniform oxide film of high-silica ...glass containing iron nano-inclusions, has been found in natural samples of the lunar regolith from Mare Crisium (Luna-24). Earlier, a high-temperature condensate was only theoretically predicted on the basis of laser evaporation experiments.
A 3-µm particle of HgS is found by electron microscopy techniques in studying the lunar regolith samples delivered by Apollo 17. It might have been preserved due to a thin cover of highly siliceous ...glass, having protective functions. This particle was likely formed from a gaseous phase by the condensation of Hg and S vapors.
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The Lonar crater (India) is the best preserved and most studied on Earth, formed in basalts, which makes it possible to conduct a comparative study with impact transformations of mineral matter on ...the Moon and other planets of the Solar System. Comparative studies have shown that impactor material, both on the Earth and on the Moon, is present in impactites not only in a geochemically dispersed form, as previously thought, but also in the form of individual submicron particles distributed in the molten target material. These are particles of native nickel, taenite, and high-nickel kamacite, which, apparently, are the transformed material of the impactor. High-nickel submicron metal inclusions are widespread in the impactites of the Lonar crater, as they were found in all studied preparations made from materials collected from different points along the rim of the crater. The high-nickel particles found in this study are an additional argument in favor of the previously stated assumption about the chondrite type of impactor.
The close intergrowth of two native alloys of the compositions Ni
0.59
Cu
0.24
Al
0.15
Fe
0.01
Mn
0.01
and Pd
0.55
Pt
0.36
Rh
0.09
with a size of 10 μm has been discovered in the regolith from the ...Mare Crisium. A conclusion on its exhalative origin is made.
