Novel experimental setup for megahertz X-ray diffraction in a diamond anvil cell at the High Energy
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Liermann, H.P.↗
Engineering topics
Langenhorst, F.
Publications and source records attributed to Langenhorst, F..
Anhydrite EOS and Phase Diagram in Relation to Shock Decomposition
In the context of the Chicxulub impact, it became recently obvious that experimental and theoretical research on the shock behavior of sulfates is essential for an assessment of the role of shock-released gases in the K/T mass extinction. The Chicxulub crater is the most important large impact structure where the bolide penetrated a sedimentary layer with large amounts of interbedded anhydrite (Haughton has also significant anhydrite in the target). The sulfuric gas production by shock compression/decompression of anhydrite is an important issue, even if the size of Chicxulub crater is only half of the so far assumed size. The comparison of experimental data for anhydrite, shocked with different techniques at various laboratories, reveals large differences in the threshold pressures for melting and decomposition. To gain insight into this issue, we have made a theoretical investigation of the thermodynamic properties of anhydrite. The project includes the review of data published in the last 40 years - reasons to study anhydrite cover a wide field of interests: from industrial problems of cement and ceramic production to the analysis of nuclear underground explosions in salt domes, conducted in the USA and USSR in the 1970th.
Ivanov, B. A.↗
Diaplectic Glass Content in Experimentally Shock-loaded Quartz Determined by X-Ray Powder Diffraction
Quartz is the most common mineral of terrestrial crustal rocks and thus a widespread indicator for impact cratering and associated shock metamorphism. Planar deformation features (PDFs) are among the most prominent and diagnostic shock features in quartz and they represent thin lamellae of glass that formed via solid-state transformations. This socalled 'diaplectic' glass becomes pervasive at higher pressures and results in optically isotropic and X-ray-amorphous phases that resemble texturally the original quartz grains (without evidence of melt flow). In the past, it has been shown that the amount of this amorphous material in experimentally shock-loaded quartz correlates with peak shock pressure. Both reports derive the glass content from density measurements of individual crystals employing the equation X(%) = (rho(sub x) - rho(sub 0))/(rho(sub x) - rho(sub gl)), where x and 0 stands for X-ray and average (optical) density, respectively. The density of glass, rho(sub gl), was adopted as 2.2 g/cu cm. Though the same procedures had been applied, the resulting glass content differs significantly among the above studies. In the present study, we are using a new approach based solely on the integral intensity of a single, carefully selected reflection in the XRD pattern, and we will compare our data to those reported in the literature.
Skala, R.↗
Orientation of Planar Deformation Features (PDFs) in quartz
Differently oriented single crystal quartz was shocked experimentally at pressures of 20 to 32 GPa and pre-shock temperatures up to 630 C. Based on this systematic investigation, we can demonstrate that the orientation of planar deformation features in quartz is not only dependent on shock pressure but also on pre-shock temperature and shock direction. Moreover, the orientation of Planar Deformation Features (PDF's) is strongly influenced by the set-up in recovery experiments. PDF's in quartz are defined as optically recognizable, planar microstructures diagnostically produced by shock compression. PDF's differ from all kinds of microstructures found in volcanic environment and therefore, their presence is a primary criterion for recognizing impact craters and ejecta layers such as the K/T boundary. Because experiments have shown a pressure dependence of the orientation of PDF's, this property is used extensively for shock wave barometry in natural impact sites. However, the unreflected application of experimental results neglects that parameters such as pre-shock temperature, shock direction, or the experimental arrangement may influence the spatial distribution of PDF's. In order to test this assumption, shock experiments on single crystal quartz at pre-shock temperatures of 20, 275, 540, and 630 C, and with shock directions (1010) and (0001) were performed. Most of the recovery experiments were carried out by using a reverberation technique, whereas in only one experiment a single shock was produced (impedance method). In the former case 0.5 mm thin discs of single crystal quartz were used, in the latter a 15 mm thick cylinder. The orientation of PDF's was measured by means of a conventional universal stage and the results are given. Effects of the experimentation technique can be derived showing the orientation of PDF's in quartz shocked at 27.5 GPa. In comparison to the well defined peaks at (1012) found in samples from reverberation experiments, the impedance matching technique causes PDF's with a broad distribution pattern and indistinct maxima. Our results have serious implications for shock-wave barometry in nature: the existing classification scheme which relates PDF orientation exclusively to shock pressure is no longer applicable. In consequence more experimental data is needed.
Langenhorst, F.↗
Influence of the preshock temperature on shock effects in quartz
Shock metamorphic features are the prime indicators for recognizing impact phenomena on Earth and other planetary bodies. Although the pressure dependence of shock features is well known, information about the influence of the preshock temperature is almost lacking. Especially in the case of large-scale impacts like Sudbury, it is expected that deep-seated crustal rocks were subjected to shock at elevated temperatures. Therefore, we continued to perform shock experiments at elevated temperatures on less than 0.5-mm thin disks of single crystal quartz cut parallel to the (1010) face. All recovered quartz samples were investigated by universal stage, spindle stage, and a newly developed density gradient technique. Errors of refractive index and density measurements are +/- 0.0005 and +/- 0.002 g/cu cm respectively. Our investigations indicate that shock metamorphic features are strongly dependent on the preshock temperature. This statement has far-reaching implications with respect to shock wave barometry that is based on data from recovery experiments at room temperature. These datasets might be applicable only to low-temperature target rocks. Moreover, this study demonstrates that shock recovery experiments are definitely required for understanding the complete pressure-temperature regime of shock metamorphism on planetary bodies.
Langenhorst, F.↗