Abstract
High-pressure glass has attracted interest in terms of both its fundamental state under extreme conditions and its possible applications as an advanced material. In this context, natural impact glasses are of considerable interest because they are formed under ultrahigh-pressure and high-temperature (UHPHT) conditions in larger volumes than laboratory fabrication can produce. Studying the UHPHT glasses of the unique giant Kara astrobleme (Russia), we found that the specific geological position of the UHPHT melt glass veins points to an origin from a secondary ultrahigh-pressure (UHP) melt according to the characteristics of the host suevites, which suggest later bottom flow. Here, we propose a fundamentally novel model involving an upward-injected UHP melt complex with complicated multi-level and multi-process differentiation based on observations of the UHP silica glass, single-crystal coesite and related UHP smectite that crystallized from an impact-generated hydrous melt. This model proposes a secondary UHP crisis during the modification stage of the Kara crater formation. The results are very important for addressing fundamental problems in fields as diverse as condensed matter states under extreme pressure and temperature (PT) conditions, material and geological reconstructions of impact structures, water conditions in mineral substances under UHP conditions in the deep Earth, and the duration and magnitude of the catastrophic effects of large asteroid impacts.
Highlights
High-pressure glass has attracted interest in terms of both its fundamental state under extreme conditions and its possible applications as an advanced material
On the basis of our field observations in 2015 and 2017 followed by detailed laboratory studies of the solidified melt material, we have identified an intrusive melt complex composed of different portions of an ascending impact melt intruding breccia and suevites for the first time in the Kara astrobleme
We propose that the obtained data on the recently discovered ultrahigh-pressure and high-temperature (UHPHT) impact glass veins in the Kara astrobleme demonstrate the formation of an upward-injected melt complex
Summary
We propose that the obtained data on the recently discovered UHPHT impact glass veins in the Kara astrobleme demonstrate the formation of an upward-injected melt complex. The presented data point to the possibility of a relatively long duration of UHP conditions for impact melts in giant astroblemes. This subject will be considered in the future development of impact models, geological reconstructions of giant impact structures and estimates of the conditions of impact structure formation, aiming to understand the environmental implications, including the possibly of multiple phases of UHP conditions. Microstructural analyses were performed in a Titan 80–300 TEM/STEM (ThermoFisher Scientific, USA) equipped with a spherical aberration corrector (probe corrector) with an accelerating voltage of 300 kV, and the STEM mode had a resolution of 0.08 nm. Simulations of the EDX patterns and images were produced using Stadelmann’s EMS software package[58]
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