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Abstract

UHPHT natural glasses are interesting not only to geologists and mineralogists, but also to physicists, chemists, and materials scientists from the point of view of the fundamental problem of the existence of matter under extreme PT-conditions. The specificity of the structure of such materials requires complex study. In this work we used optical, electron and atomic force microscopy, as well as Raman spectroscopy to assess the phase separation in UHPHT glasses of the Kara astrobleme. Their microscopic images show the separation of disordered aluminosilicate and silicate phases, their heterogeneous and partially heterogeneous structure with domain sizes of several tens of nanometers. The revealed highest structural homogeneity at the nanoscale level of UHPHT vein silica impact glasses, compared to high-pressure and low-pressure silica-rich glasses, confirms the specificity of the formation of UHPHT glasses and indicates promising further physical studies of this natural material to analyze the matter at ultra-high pressure conditions.
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... Investigations of impact structures allow the search for new concepts of crater formation on Earth and give useful information about the structure and evolution of the lithosphere, as well as the solution of important issues of the formation of planets in the solar system. Impactites are the result of impact melting of the silicate rocks under high pressure and temperature (see, e.g., Dence, 1971;Golubev et al., 2020;Osinski et al., 2013) and contain glasses and remelted minerals embedded into the matrix. ...
... Therefore, the study of the impact melt rocks and shock metamorphic materials from the impact craters using various spectroscopic and structural techniques is of interest to extract important information about variations of chemical composition, and structural and physical parameters resulting from impact melt rocks formation. For these reasons, various features of different impact melt rocks (impactites and tektites) were studied by chemical analysis, scanning and transmission electron microscopy, Raman spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction (XRD), 57 Fe M€ ossbauer spectroscopy, and some other techniques (see, e.g., Bustamante et al., 2005;Ding & Veblen, 2004;Dunlap et al., 1998;Dunlap & McGraw, 2007;Dunlap & Sibley, 2004;Golubev et al., 2019Golubev et al., , 2020Loayza & Cabrejos, 2014;Ostroumov et al., 2002;Shumilova et al., 2018;Verma et al., 2008). ...
... A hump at the diffraction pattern in the 2Θ range of 20-40°indicates the presence of an amorphous component in the sample. A similar amorphous halo was observed in the XRD patterns of impact melts from Kara astrobleme and Ries crater (Golubev et al., 2020;Shumilova et al., 2018). Reflections of crystalline phases are visible against the background of the amorphous halo. ...
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Iron‐bearing phases in the impact melt rock (impactite) from Jänisjärvi astrobleme (Karelia, Russian Federation) were studied by optical microscopy, electron probe microanalysis, Raman spectroscopy, X‐ray diffraction, and 57Fe Mössbauer spectroscopy. The phase composition and the contents of elements were determined in the studied impactite. The Raman spectra of cordierite, chamosite, and ilmenite in the impact melt rock were measured and analyzed. The 57Fe Mössbauer spectrum of Jänisjärvi impactite demonstrated the presence of different iron microenvironments in the iron‐bearing phases in the impact melt rock, which were assigned to cordierite; the M1, M2, M3, and M4 sites in chamosite; ilmenite; and ferrihydrite.
... In the Raman spectra of the Kara UHPHT glasses [16], in addition to vibrational bands of the SiO4-framework in the region of 400-800 cm -1 , the stretching band of Si-OH groups (960-970 cm −1 ) and the bands related to the vibrations of SiO4 groups with 1, 2 and 4 non-bridging oxygen atoms (so-called Q 3 , Q 2 and Q 0 units) were identified in the range of 800-1200 cm -1 . Interestingly, in the Raman spectra of aluminosilicate and pure silicate fragments of the Kara glass, the band shapes in the range of 800-1200 cm -1 were almost identical, with a small predominance of Q 2 and Q 3 units over Q 0 in the former and their uniform distribution in the latter. ...
... The discovery of a high concentration of non-bridging oxygen atoms was highly unexpected based on the results [17] used for the interpretation of Raman spectra. In addition, electron microscopic images presented in [13,16] showed the presence of widespread pyroxene (Q 2 ) microcrystallites in the glass matrix. These observations call for further investigation of the polymerization of the UHPHT impact Kara glasses. ...
... UHPHT melt impact glasses were sampled in 2015 and 2017 from impactites of the southern sector of the Kara crater from vein bodies cutting suevite massif ( Figure 1) at the Kara River (Pay-Khoy, Russia) and these are samples KP15-12-115 and KP15-12-118. A preliminary analysis of the structural state of these glasses was carried out using a set of standard mineralogical research methods [13,14,16]. The main feature distinguishing UHPHT melts from clast type glasses and massive melt impactites was found to be the multilevel differentiation of impact melt, including liquation of silicate and aluminosilicate melts and partial silica melt crystallization to UHP SiO2 variety-monocrystalline coesite [13,14]. ...
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