Impact spallation – completely underestimated by impact researchers.
Left, from the top down: Shock spallation experiment producing typical open tensile fractures. – Spallation fractures in shocked quartzite cobble, Azuara/Rubielos de la Cérida impact event (Spain). Microscopic shock spallation in sandstone quartz grains, Rubielos de la Cérida impact basin. – To the right: Local megascopic impact spallation in well-bedded Jurassic limestones; Azuara (Spain) impact structure northern rim region south of Fuendetodos. Link to a full article on impact spallation.
Impact sulfate melt rock from the Rubielos de la Cérida impact basin (Azuara impact event, Spain) – a rare meteorite impact signature
Strongly shocked quartzite clasts in the low-density, highly porous CaSO4 matrix.
Clast of sulfate melt rock in the Barrachina megabreccia -The sulfate melt rock under the SEM. Note the vesicular texture. – More about Azuara and Rubielos de la Cérida impact melt rocks (carbonate melt, carbonate-phosphate melt, silicate melt, carbonate-psilomelan melt).
Polymictic impact breccia dike sharply cutting through well-bedded Muschelkalk limestone. – Rubielos de la Cérida impact basin (Spain) near Olalla.
Very nice example of the many breccia dikes in the Spanish Azuara impact structure and the Rubielos de la Cérida impact basin (crater chain). – More about impressive breccia dikes (dike breccias) in the Rubielos de la Cérida basin and the Azuara structure.
Diametral radargram across one of the most spectacular craters in the Chiemgau meteorite impact strewn field. Loamy-gravelly target material. Impact melt rocks, strong shock metamorphism. Strong reflectivities down to several meters depth are explained by extreme high-temperature sintering of the underground material. Note the complex excavation with the ring wall wandering outwards (as indicated with “real reflections”). 25 MHz center frequency with modulated 200 MHz.
More about GPR measurements over young meteorite craters: Click HERE
Chiemite – carbon impact rock (impactite) – the Chiemgau impact event as namesake
REM image. – Formation in spontaneous shock carbonization of the vegetation in the impact area. Investigations at the Diamond Laboratory, Geological Institute, Russian Academy of Science Syktyvkar, with optical and atomic force microscopy (AFM), X-ray fluorescence spectroscopy (RFA), scanning electron (SEM) and transmission electron (TEM) microscopy, high-resolution Raman spectroscopy, X-ray diffraction (XRD) and differential thermal analysis (DTA) as well as δ13C and 14C radiocarbon isotope data analysis.
Approx. 95% carbon; detection of diamond and carbyne; formation conditions for the latter 2500 – 4000°C and some GPa pressure.
Very “smart” people are still of the opinion that it is coke. Take a look at that too: file: EGU 2019 chiemite poster.pdf – Wikipedia
SEM detail view of the chiemite.
An extensive article on the chiemite has recently been published in print:
Using shock effects in quartz as an impact indicator has a long tradition. They are created in the first phase of impact cratering (contact and compression phase) and produce well known PDFs, PFs and diaplectic glasses in various minerals. The fact that thermal shock has so far been virtually ignored in impact research is due to the fact that the effects mentioned above precede thermal shock during pressure release. However, if extreme shock pressures lead to melting and vaporization of the rocks (> roughly 50 GPa), violent thermal shock can occur when slightly or not at all shocked material is immersed in melt and/or vapor. In anticipation of a publication, some photomicrographs of isolated quartz grains from meteorite impact sites are shown here, which have obviously experienced such a short thermal shock and reveal quite unusual micro-fracturing patterns.
Photomicrographs (crossed polarizers): Isolated quartz grains (size about 1 mm) “floating” in a fine grained matrix. In many of the grains this micro-fracturing is more or less sharply limited to a concentric rim zone encasing a largely untouched core with a few sub-planar fractures in some cases. Chrudim impact, Czech Republic.
Quartz grains from the same impact site showing irregular micro-fracturing that merges into sets of planar fractures (PF) after the rhombohedron.
Saarland impact: Quartz grains in impact melt nearly pulverized by extreme micro-fracturing.
Impact shock feature: ballen structures from four new impact sites in Central Europe (Germany, Czech Republic)
Ballen structures in silica form a characteristic texture in quartz that in general is considered a result from various stages of phase transformation and recrystallization of amorphous silica like e.g., diaplectic glass and hence are regarded as shock indicator. A different model has recently been suggested that proposes a formation of ballen in quartz in an extreme thermal shock event.
Ballen structures (photomicrographs, plane light and crossed polarizers; field width 560 µm). – Saarland (Nalbach, Saarlouis) impact.
Ballen structures impact merging into tridymite and cristobalite.(photomicrographs, crossed polarizers and plane light; field width 1.4 mm). – Saarland (Nalbach, Saarlouis) impact.