Spectroscopic features of ultrahigh-pressure impact glasses of the Kara astrobleme

Abstract

The state of substances under ultrahigh pressures and temperatures (UHPHT) now raises a special interest as a matter existing under extreme conditions and as potential new material. Under laboratory conditions only small amounts of micrometer-sized matter are produced at a pressure up to 100 GPa and at room temperature. Simultaneous combination of ultrahigh pressures and temperatures in a lab still requires serious technological effort. Here we describe the composition and structure of the UHPHT vein-like impact glass discovered by us in 2015 on the territory of the Kara astrobleme (Russia) and compare its properties with impact glass from the Ries crater (Germany). A complex of structural and spectroscopic methods presents unusual high pressure marks of structural elements in 8-fold co-ordination that had been described earlier neither in synthetic nor natural glasses. The Kara natural UHPHT glasses being about 70 Ma old have well preserved initial structure, presenting some heterogeneity as a result of partial liquation and crystallization differentiation where an amorphous component is proposed to originate from low level polymerization. Homogeneous parts of the UHPHT glasses can be used to deepened fundamental investigation of a substance under extreme PT conditions and to technological studies for novel material creations.

Mysterious long-living ultrahigh-pressure or secondary impact crisis

“…As mentioned above, a typical impact UHP stage lasts just a fraction of a second. The common melt rocks in the Kara astrobleme, including massive melt bodies and clastic glasses 25 , do not feature evidence of long-duration UHP conditions, do not contain melt-crystallized coesite and have different chemical compositions. Therefore, the initial impact melt did not experience long-duration UHP conditions and cannot have been the source of the studied UHPHT glass veins.…”

“…Among the numerous known impact structures, the Kara astrobleme (Russia) is one of the largest astroblemes in which ultrahigh-pressure and high-temperature (UHPHT) glasses have been found 25 . Based on the SiO 2 phase state diagram 15,19 , previous experiments, the definition of an emerging shock temperature during the impact, and theoretical calculations 26 , the observed coesite in the SiO 2 glasses of the Kara astrobleme 20,25,27 correspond to an impact-induced melt temperature greater than 1700 °C. Thus, the impact melt products of the Kara astrobleme are very attractive from not only a fundamental point of view but also considering the probable practical use of impact glass 25 .…”

“…A very specific feature of the found upward-injected melt glass veins is the presence of ultrahigh-pressure (UHP) phases, such as impact diamonds and melt-crystallized coesite 25,27,39 . The latter suggests that the www.nature.com/scientificreports www.nature.com/scientificreports/ cross-cutting melt veins could not have been associated with any hydrothermal activity and must have a high-pressure melt origin, which we discuss below.…”

“…5). The total chemical composition of the aluminosilicate and phase state based on X-ray diffraction are presented in our previous work 25 . In the same paper, it was noted that the glass veins had unusual 8-fold co-ordination sites of Fe 2+ , which had not been described before in either synthetic or natural glasses.…”

X-ray computed microtomography of diamondiferous impact suevitic breccia and clast-poor melt rock from the Kara astrobleme (Pay-Khoy, Russia)

“…4). According to the data from silicate rock analysis and energy dispersive spectral analysis, the suevites and melt rocks of the Kara astrobleme are mainly represented by an aluminosilicate component with admixtures of silicate, carbonate, and sulfide components (Shumilova et al, 2018b). To supplement the specifics of previously identified varieties of suevites, we determined the nature of the distribution of each of these components, which primarily depended on the phase contrast on the tomograms.…”