In the future we will present interesting pictures – megascopic to microscopic – from the world of our impact research in roughly weekly intervals. A small accompanying text explains the presentation and, where appropriate, links to further pages are given. New image (18.1. 2020):
Impact feature: thermal shock in quartz
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.
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:
Enigmatic Glass‐Like Carbon from the Alpine Foreland, Southeast Germany: A Natural Carbonization Process.
Ground Penetrating Radar (GPR): Emmerting #004 crater, Chiemgau meteorite impact strewn field (Bavaria, Southeast Germany)
Ground Penetrating Radar (GPR) – meteorite crater Chiemgau impact
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
Impact breccia in lapillistone matrix. – Rubielos de la Cérida impact basin (Spain) near Olalla.
Muschelkalk breccia-within-breccia, lapillistone matrix (accretionary lapilli).
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.
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).
Trigonal and cubic Fe2Si polymorphs (hapkeite) in the eight kilograms find of natural iron silicide – a probably new class of meteorites
Excavated from the Chiemgau impact crater strewn field: 8 kg (eight – no printer’s error) iron silicide chunk.
Click presentations: 50th Lunar & Planetary Science Conference (LPSC):
Enigmatic Impact Breccias Probably Linked to the Ries Crater (Germany) Impact Event -Alemonites from Bavaria and sunstones from the Czech Republic
Alemonite (DE) and sunstone (CZ) samples from the field
Shock effects in alemonites and sunstones
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.
Rock fluidization, Azuara Impact Structure (Spain)
Rock fluidization in strongly competent limestones/dolostones (Muschelkalk Fm.); Monforte de Moyuela, Azuara impact structure, Spain. See article Rock fluidization during peak-ring formation of large impact structures by U. Riller et al. Also focus on Acoustic fluidization (H.J. Melosh). Enlarged image.
Shock effect in calcite. Multiple sets of closely spaced planar features (micro twins). The width of the twins is of the order of only one micrometer. Thin section micrograph, crossed polarizers. From a polymictic breccia, rim region of the Rubielos de la Cérida impact basin crater chain.