NMR Spectral Characteristics of Ultrahigh Pressure High Temperature Impact Glasses of the Giant Kara Crater (Pay-Khoy, Russia)

In this study, we carried out the analysis of the impact melt vein glasses from the Kara impact crater (Russia) in comparison to low-pressure impact melt glasses (tektites) of the Zhamanshin crater (Kazakhstan). 27Al, 23Na, and 29Si MAS NMR spectra of the samples of these glasses were analyzed. The samples of the natural glass contained inclusions of crystalline phases, paramagnetic elements that greatly complicate and distort the NMR signals from the glass phase itself. Taking into account the Mossbauer distribution of Fe in these glasses, the analysis of the spectra of MAS NMR of glass network-former (Si, Al) and potential network-modifiers (Na) of nuclei leads to the conclusion that the Kara impact melt vein glasses are characterized by complete polymerization of (Si,Al)O4 tetrahedral structural units. The NMR features of the glasses are consistent with the vein hypothesis of their formation under conditions of high pressures and temperatures resulting in their fluidity, relatively slow solidification with partial melt differentiation, polymerization, and precipitation of mineral phases as the impact melt cools. The 70 Ma stability of the Kara impact vein glass can be explained by the stabilization of the glass network with primary fine-dispersed pyroxene and coesite precipitates and by the high polymerization level of the impact glass.

Possible shock-induced crystallization of skeletal quartz from supercritical SiO2-H2O fluid: A case study of impact melt from Kamil impact crater, Egypt

Since its discovery, the Kamil crater (Egypt) has been considered a natural laboratory for studying small-scale impact cratering. We report on a previously unknown shock-related phenomenon observed in impact melt masses from Kamil; that is, the shock-triggered formation of skeletal quartz aggregates from silica-rich fluids. These aggregates are unshocked and characterized by crystallographically oriented lamellar voids and rounded vesicles. The distribution of the aggregates can be correlated with former H2O- and impurity-rich heterogeneities in precursor quartz; i.e., fluid inclusions. The heterogeneities acted as hot spots for local melting. Due to the presence of H2O and the high impact pressure and temperature, the formation of a localized supercritical fluid is plausible. Below the upper critical end point of the SiO2–H2O system (temperature <1100 °C and pressure <1 GPa), SiO2 melt and H2O fluid become immiscible, leading to the rapid and complete crystallization of skeletal quartz.

Supplemental Material: Possible shock-induced crystallization of skeletal quartz from supercritical SiO2-H2O fluid: A case study of impact melt from Kamil impact crater, Egypt

Description of the analytical methods, and five supplemental figures.<br>

Supplemental Material: Possible shock-induced crystallization of skeletal quartz from supercritical SiO2-H2O fluid: A case study of impact melt from Kamil impact crater, Egypt

Description of the analytical methods, and five supplemental figures.<br>

Comparative Characteristics of Structural-Textural, Mineralogical and Petrochemical Features of Melt Rock Impactites of the Kara Astrobleme. Preliminary Data (Pay-Khoy, Russia)

The Kara astrobleme is one of the largest astroblemes known on land. Its diameter is ~65 km, the age is about 70 million years. The astrobleme is located at the northeastern part of the Pay-Khoy anticlinorium at the Kara River mouth region (Kara Sea coast, Russia). It is a unique object of impact genesis due to the presence of a variety of suevites and melt impactites. Melt rocks are products of the highest degree of impact transformation of target rocks. The diversity of melt rock impactites of the Kara astrobleme and obtaining their complex comparative mineralogical and petrochemical characteristics are important for solving the fundamental problem for studying of the typomorphism of the impactitogenesis products of melt rocks both – the impactites of the Kara astrobleme and other astroblemes in general. In the Kara astrobleme region there are at list two different types of massive melt rocks bodies – a cover melt rock at the Anaroga River (I) studied by previous researchers and an unexplored body of melt rock impactite at the Kara River (II) spatially connected with ultrahigh-pressure high-temperature (UHPHT) glasses just recently discovered. Our preliminary data indicate that the melt rock varieties of the Kara astrobleme have significant differences in texture and structure. The considered melt rocks are mostly composed of a matrix represented by a “mixture” of amorphous and cryptocrystalline masses of predominantly feldspar composition with a subordinate SiO2 content. According to the data of energy dispersive analysis the compositions of the studied melt rocks are similar and have minor deviations within the first percent. The difference in the shape of silicate segregations in melt rocks may indicate that the impact melt could have a high temperature with a shorter time interval for the solidification of melt rock II on the Kara River, in contrast to the massive melt rock I on the Anaroga River, where the impact melt had large volume and, accordingly, was cooled longer at lower temperatures. The data obtained complement the specificity of the Kara melt impactites, which may play a role in complementing the geological model of the Kara astrobleme. The reported study was funded by RFBR, project number 20-35-90065; the analytical equipment has been used at the Center for Collective Use “Geonauka” (IG Komi FRC SC UB RAS, Syktyvkar, Russia); the author expresses his gratitude to Isaenko S.I. for analytical work using Raman spectroscopy; Tropnikov E.M. for help in performing microprobe studies.

Preliminary Petrological and Geochemical Studies of Dolerite Dikes at the Kara Astrobleme Central Uplift, Comparison with UHPHT Impact Melt Glasses (Pay-Khoy, Russia)

Recent find of the ultra-high pressure high-temperature (UHPHT) impact melt glasses among the impactites of the Kara astrobleme has a high interest in nicely preserved 70 Ma glass with potentially unusual structure and properties. By the moment, it is important to understand about the substance source for the UHPHT glasses. The Kara target is characterized with complicated rock material preferably presented with Paleozoic sedimentary units. At the same time, the target has in a sequence Devonian sills and dikes of gabbro-dolerites. The latter appear on the surface at the Kara dome being a material which probably have been affected by the most strong impact. Here we for the first time describe the results of preliminary analysis of petrological and geochemical features of the magmatic dikes of the central uplift with the aim to understand their probable genetic source for the UHPHT impact melt veins matter. The provided studies point to essential difference between the compared materials, that means the UHPHT impact melts do not correspond to the magmatic material of the Khengursky complex of gabbro-dolerites of the Pay-Khoy Ridge (Russia).

Petrography and Shock Metamorphism of the Lunar Breccia Meteorite NWA 13120

Lunar meteorites are the fragments of rocks that fell on Earth because of the impacts of asteroids on the Moon. Such rocks preserve information about the composition, evolutionary process, and shock history of the lunar surface. NWA 13120 is a recently discovered lunar breccia meteorite having features of strong shock, which is composed of lithic and mineral clasts in a matrix of very fine-grained (<10 μm) and recrystallized olivine-plagioclase with a poikilitic-like texture. As the most abundant lithic clasts, the crystalline impact melt (CIM) clasts can be divided into four types according to their texture and mineral composition: (1) anorthosites or troctolitic anorthosite with a poikilitic-like texture, but the mineral content is different from that of the matrix; (2) anorthosites containing basaltic fragments and rich in vesicles; (3) troctolitic anorthosite containing metamorphic olivine mineral fragments; (4) troctolitic anorthosite containing troctolite fragments. Based on the petrology and mineralogy, NWA 13120 is a lunar meteorite that was derived from the ferrous anorthosite suite (FANs) of the lunar highlands, while its texture suggests it is a crystalline impact melt breccia. In addition, we infer that the parent rock of NWA 13120 is a lunar regolith breccia enriched in glass fragments. During the shock process, at pressures of more than 20 GPa, all plagioclase fragments were transformed into maskelynites, and olivine fragments occurred metamorphism. The post-shock temperature led to the partial melting of the basaltic fragments. Subsequently, all glass with diverse components in the parent rock were devitrified and recrystallized, forming the common olivine-plagioclase poikilitic-like texture and different CIM clasts. Meanwhile, the devitrification of maskelynite formed the accumulation of a large number of plagioclase microcrystals. Therefore, NWA 13120 is a meteorite of great significance for understanding the local shock metamorphism of lunar rocks on the lunar surface.

Mineralogical and chemical properties inversed from 21-lunar-day VNIS observations taken during the Chang’E-4 mission

We report on the mineralogical and chemical properties of materials investigated by the lunar rover Yutu-2, which landed on the Von Kármán crater in the pre-Nectarian South Pole–Aitken (SPA) basin. Yutu-2 carried several scientific payloads, including the Visible and Near-infrared Imaging Spectrometer (VNIS), which is used for mineral identification, offering insights into lunar evolution. We used 86 valid VNIS data for 21 lunar days, with mineral abundance obtained using the Hapke radiative transfer model and sparse unmixing algorithm and chemical compositions empirically estimated. The mineralogical properties of the materials at the Chang’E-4 (CE-4) site referred to as norite/gabbro, based on findings of mineral abundance, indicate that they may be SPA impact melt components excavated by a surrounding impact crater. We find that CE-4 materials are dominated by plagioclase and pyroxene and feature little olivine, with 50 of 86 observations showing higher LCP than HCP in pyroxene. In view of the effects of space weathering, olivine content may be underestimated, with FeO and TiO2 content estimated using the maturity-corrected method. Estimates of chemical content are 7.42–18.82 wt% FeO and 1.48–2.1 wt% TiO2, with a low-medium Mg number (Mg # ~ 55). Olivine-rich materials are not present at the CE-4 landing site, based on the low-medium Mg #. Multi-origin materials at the CE-4 landing site were analyzed with regard to concentrations of FeO and TiO2 content, supporting our conclusion that the materials at CE-4 do not have a single source but rather are likely a mixture of SPA impact melt components excavated by surrounding impact crater and volcanic product ejecta.

Young craters of Mercury correlating with offset magnetic anomalies

&lt;p&gt;In the last months of its mission, MESSENGER was able to obtain measurements at low altitude (&lt; 120 km). This has made it possible to measure small magnetic field signals, probably of crustal origin (Johnson et al, 2015). Maps of the crust signatures at 40 km altitude were produced by Hood (2016) and Hood et al. (2018), showing that the strongest anomalies are about 9 nT in the Caloris basin. Some of the anomalies are associated with impact craters, and it has been demonstrated that this is not a coincidence (Hood et al., 2018). It is believed that these anomalies are the result of impactor materials rich in magnetic carriers (e.g., metallic iron) that were incorporated on the surface acquiring remanent magnetic fields during the cooling of the material. We analyzed whether the anomalies of the crustal field are related to geological characteristics by examining two Hermean craters in order to test this impactor hypothesis. Anomalies associated with Rustaveli and Stieglitz craters are slightly or totally asymmetric with respect to the crater center. The morphology and geological setting of these two fresh impact craters that still maintain a well-preserved ejecta blanket and visible secondary crater chains are investigated to constrain the overall impact dynamics. In both cases, slight asymmetries in the morphology and ejecta distribution show that the magnetic anomalies correlate well with the location of impact melt. Rustaveli is associated with a ~5 nT crustal magnetic anomaly centered close to the crater&amp;#8217;s midpoint, although offset ~20 km east-southeast. This offset is somewhat consistent with the downrange direction implied by Rustaveli&amp;#8217;s impact melt and crater chains distribution. For Stieglitz, an anomaly larger than 3 nT includes most of the ejecta melt locations towards southwest. The ejecta melt cluster to the north of the crater corresponds to an anomaly of ~5 nT, while the largest anomaly of ~7 nT is found further north and closely corresponds to the crater&amp;#8217;s deepest chain. For both craters, the melt likely recorded the prevailing magnetic field of Mercury after quenching. Hence, both impactors brought magnetic carriers to the surface that could record the past magnetic field of Mercury.&lt;em&gt; Acknowledgments:&lt;/em&gt; &lt;em&gt;The authors gratefully acknowledge funding from the Italian Space Agency (ASI) under ASI-INAF agreement 2017-47-H.0 and the European Union&amp;#8217;s Horizon 2020 research and innovation programme under grant agreement No. 776276.&lt;/em&gt;&lt;/p&gt; &lt;p&gt;Hood, J. Geophys. Res. Planets 121, 2016;&lt;br /&gt;Hood et al., J. Geophys. Res. Planets 123, 2018;&lt;br /&gt;Johnson et al., Science 348, 2015.&lt;/p&gt;