Schokverschijnselen in kwarts als bewijs voor een meteorietinslag

Deformatiestructuren in kwarts die gevormd zijn onder extreem hoge temperatuur en druk zijn aanwijzingen voor meteorietinslagen op aarde. Maartje Hamers van de Universiteit Utrecht doet onderzoek aan deze ‘schokverschijnselen’. Zij probeert door kwarts op verschillende manieren te onderzoeken nieuwe en minder kostbare technieken te ontwikkelen om inslagkraters te kunnen herkennen

Identifying shock microstructures in quartz from terrestrial impacts: new scanning electron microscopy methods

Terrestrial impact craters and ejecta layers are widely studied, both as an analogue to craters on other rocky planets, moons and asteroids and for their relevance to the geology of the Earth. Therefore, the correct identification of impact structures and ejecta layers on the Earth is essential, but recognition of the characteristic circular crater morphology is often hindered by erosion and deformational processes. One of the most reliable impact indicators is the presence of shock metamorphosed minerals in target rocks and in material ejected out of the crater. Of the minerals that can show these shock effects quartz is most widely studied. A wide variety of shock effects can form in quartz at different peak shock pressures. Especially planar deformation features (PDFs - originally amorphous microlamellae) are universally accepted as the most reliable form of impact evidence. In a light microscope distinction between PDFs and other, non-shock related (sub-)planar microstructures in quartz is not always possible. To prove the shock origin of planar microstructures in quartz, time-consuming, difficult and expensive transmission electron microscopy (TEM) analysis of the lamellae is often required. Scanning electron microscopy (SEM) techniques, on the other hand, are relatively easy and quick. The aim of the research presented in this thesis is to develop SEM methods for the reliable identification and characterisation of shock microstructures in quartz, in particular PDFs, as an alternative and addition to existing TEM techniques. The SEM techniques include cathodoluminescence (CL) and forescattered electron (FSE) imaging and electron backscatter diffraction (EBSD) mapping. Focussed ion beam preparation of TEM foils allows direct correlation of information obtained using the SEM to the microstructures analysed using TEM. The combination of CL, FSE and EBSD techniques and more standard applications in the SEM, such as backscattered and secondary electron imaging, provides a powerful and easy to use, non-destructive integrated approach for studying shock microstructures in quartz. Direct correlation with light microscopy is possible, because standard petrographic thin sections can be studied in both the light microscope and the SEM. The combined SEM techniques described in this thesis bridge the gap between highly detailed TEM analysis and general observations in light microscopy that are relevant for larger sample volumes. Combined SEM and TEM observations on shocked quartz grains show combinations of microstructures that can be related to different stages of healing in grains shocked to moderate and high pressure and suggest that mechanical twinning in the low shock pressure regime may play a more important role in PDF development than previously assumed. For the identification and general characterisation of shock microstructures in quartz, SEM analysis using CL and FSE imaging and EBSD mapping is sufficient. This conclusion is a major step forward for terrestrial impact research and will contribute to the reliable identification of proposed impact structures and ejecta layer

Scanning electron microscope-cathodoluminescence (SEM-CL) imaging of planar deformation features and tectonic deformation lamellae in quartz

Planar deformation features (PDFs) in quartz are essential proof for the correct identification of meteorite impact structures and related ejecta layers, but can be confused with tectonic deformation lamellae. The only completely reliable method to demonstrate the shock origin of suspected (sub-) planar microstructures, transmission electron microscope (TEM) observations, is costly and time consuming. We have used a cathodoluminescence (CL) detector attached to a scanning electron microscope (SEM) to image both PDFs and tectonic deformation lamellae in quartz to demonstrate the potential of a simple method to identify PDFs and define characteristics that allow their distinction from tectonic deformation lamellae. In both limited wavelength grayscale and composite color SEM-CL images, PDFs are easily identified. They are straight, narrow, well-defined features, whereas tectonic deformation lamellae are thicker, slightly curved, and there is often no clear boundary between lamella and host quartz. Composite color images reveal two types of CL behavior in PDFs: either they emit a red to infrared CL signal or they are nonluminescent. The color of the CL signal emitted by tectonic deformation lamellae ranges from blue to red. For comparison, we also imaged several shocked quartz grains at cryogenic temperature. In most cases, the PDF characteristics in cryo-CL images do not differ significantly from those in images recorded at room temperature. We conclude that SEM-CL imaging, especially when color composites are used, provides a promising, practical, low cost, and nondestructive method to distinguish between PDFs and tectonic lamellae, even when the simplest CL techniques available are used

Shocked quartz in the SEM: Distinction between amorphous and healed PDFs

Combined SEM techniques show that different CL signatures of PDFs are related to fresh and healed microstructures of PDFs and host quartz. This is confirmed by TEM results. A combination of SEM techniques can give the same type of information as TE

The Guarda structure (Portugal): Impact structure or not? Microstructural studies of Quartz, Zircon and Monazite

The Guarda Structure in north-eastern Portugal has been proposed as a potential impact structure. We have studied the structure in detail, but no field or microscopic evidence has been found to support the impact hypothesi

Gastrointestinal digestion of dietary advanced glycation endproducts increases their pro-inflammatory potential

Thermal treatment of food products leads to the formation of dietary advanced glycation endproducts (dAGEs). It was previously shown that dAGEs induce TNF-α secretion in human macrophage-like cells. To what extent gastrointestinal digestion of dAGEs influences these pro-inflammatory effects and what the implications of these pro-inflammatory characteristics further down the human gastrointestinal tract are, are currently unknown. In one of our previous studies, dAGEs were digested using the TNO gastroIntestinal Model and analysed for dAGE quantity after digestion. In the current study both digested and undigested dAGEs were used to expose human macrophage-like cells, which were subsequently analysed for TNF-α secretion. In addition, the obtained digests were fractionated, and human macrophage-like cells were exposed to the different fractions to determine whether specific fractions induce TNF-α secretion. The results show that digested dAGEs have an increased pro-inflammatory effect on human macrophage-like cells compared to undigested dAGEs. This paper therefore shows that the digestion of food-components, and specifically dAGEs, plays an important role in determining their biological activity

Identifying shock microstructures in quartz from terrestrial impacts: new scanning electron microscopy methods

Terrestrial impact craters and ejecta layers are widely studied, both as an analogue to craters on other rocky planets, moons and asteroids and for their relevance to the geology of the Earth. Therefore, the correct identification of impact structures and ejecta layers on the Earth is essential, but recognition of the characteristic circular crater morphology is often hindered by erosion and deformational processes. One of the most reliable impact indicators is the presence of shock metamorphosed minerals in target rocks and in material ejected out of the crater. Of the minerals that can show these shock effects quartz is most widely studied. A wide variety of shock effects can form in quartz at different peak shock pressures. Especially planar deformation features (PDFs - originally amorphous microlamellae) are universally accepted as the most reliable form of impact evidence. In a light microscope distinction between PDFs and other, non-shock related (sub-)planar microstructures in quartz is not always possible. To prove the shock origin of planar microstructures in quartz, time-consuming, difficult and expensive transmission electron microscopy (TEM) analysis of the lamellae is often required. Scanning electron microscopy (SEM) techniques, on the other hand, are relatively easy and quick. The aim of the research presented in this thesis is to develop SEM methods for the reliable identification and characterisation of shock microstructures in quartz, in particular PDFs, as an alternative and addition to existing TEM techniques. The SEM techniques include cathodoluminescence (CL) and forescattered electron (FSE) imaging and electron backscatter diffraction (EBSD) mapping. Focussed ion beam preparation of TEM foils allows direct correlation of information obtained using the SEM to the microstructures analysed using TEM. The combination of CL, FSE and EBSD techniques and more standard applications in the SEM, such as backscattered and secondary electron imaging, provides a powerful and easy to use, non-destructive integrated approach for studying shock microstructures in quartz. Direct correlation with light microscopy is possible, because standard petrographic thin sections can be studied in both the light microscope and the SEM. The combined SEM techniques described in this thesis bridge the gap between highly detailed TEM analysis and general observations in light microscopy that are relevant for larger sample volumes. Combined SEM and TEM observations on shocked quartz grains show combinations of microstructures that can be related to different stages of healing in grains shocked to moderate and high pressure and suggest that mechanical twinning in the low shock pressure regime may play a more important role in PDF development than previously assumed. For the identification and general characterisation of shock microstructures in quartz, SEM analysis using CL and FSE imaging and EBSD mapping is sufficient. This conclusion is a major step forward for terrestrial impact research and will contribute to the reliable identification of proposed impact structures and ejecta layer