Colloid Geochemistry of Silica

Recent investigations indicate the importance of meteorite impact as a process which has operated throughout geologic time to produce numerous originally circular structures as much as 50 km in diameter. One such structure, at Sudbury, Ontario, is associated with large volumes of internally derived igneous rock. Geological and experimental studies have demonstrated that rocks subjected to intense shock waves produced by hypervelocity meteorite impacts and by nuclear or chemical explosions develop distinctive and uniqueshock-metamorphic features, including: (1) high-pressure minerals such as coesite and stishovite; (2) crystal lattice deformation features such as isotropic feldspar (maskelynite) and « planar features » (shock lamellae) in quartz; (3) ultra-high-temperature reactions not produced by normal geological processes, such as decomposition of zircon to baddeleyite and melting of quartz to lechatelierite. These petrographic features, currently regarded as unequivocal evidence for meteorite impact, can be preserved and recognized even in very old and deeply eroded structures. Such features have now been observed in more than 50 « crypto-explosion » structures ranging in size from 2 km to more than 60 km in diameter. The recent discovery of shock-metamorphic features in rocks of the Sudbury structure, Ontario, indicates that this old and complex structure was also produced by a large meteorite impact. Petrographic shock effects are widespread in inclusions of « basement » rock in the Onaping « tuff », a unit now regarded as afallback breccia deposited in the original crater immediately after impact. Similar shock effects also occur in the footwall rocks around the basin, associated with shatter cones and unusual Sudbury-type breccias. Study of Sudbury specimens has establishedgrades of progressive shock metamorphism comparable to those recognized at younger impact structures (Brent, Ontario; Ries basin, Germany). Igneous activity associated with known meteorite impact structures takes two forms: The inferred development of the Sudbury structure was a complex process involving: (1) impact of an asteroidal body, forming a large (100-km) diameter crater with a central uplift; (2) subsidence of the central uplift and simultaneous emplacement of the Nickel Irruptive; (3) metamorphism, deformation, and erosion to its present appearance. The post-impact history of the Sudbury structure thus corresponds closely to that established for many ring-dike complexes and caldera subsidences. Similar compound impact-igneous structures, in which internal igneous activity is superimposed on a large impact crater, probably exist on both the earth and the moon. Future examination of « roofed lopoliths » and « ring-dike structures » for shock-metamorphic effects, combined with serious consideration of the geophysical effects produced by large-energy meteorite impacts, will be a productive field for cooperative studies by astrogeologists and igneous petrologists.

Ciletuh is a geopark area in West Java that has a semicircle-shaped cliff called mega-amphitheater. Morphogenesis of the amphitheater is still unknown. One possible cause is a meteorite impact that triggered a mega slump. This study aims to collect the evidence of meteorite impact. It has significant value for the geology of Indonesia since this region not yet has confirmed impact crater. In this research, image analysis from satellite remote sensing is used for identification of meteorite impact geomorphology. An analysis based on DEM unveils a ring morphology, a possible clue of an impact crater. The depression zone surrounded by a circular shape with an uplift area in the middle resembles characteristics of the complex impact crater. Meandering Ciletuh river indicates a compression due to a slump towards the southwest. Reconstruction of possible position toward the northeast (before slump deformation occurred) shows a clearer possible meteorite impact crater. A ground checking of identified structure proves that a bowl-shaped morphology found at the possible impact crater. Some steep dip structures have found, these might be due to an impact that causes the orientation of the structure to be upright. A stone that resembles the shatter-cone is found in the melange area. The melange is believed as a product of a sea trench million years ago. By using meteorite impact theory, it is also possible that the melange is a kind of impact breccia. This feature adds uniqueness to Ciletuh as a geopark.

Introduction Lonar crater in India offers important mineralogy insights into impact-related processes. One of the key minerals found within the crater is maskelynite, a high-pressure diaplectic glass formed by shock metamorphism during meteorite impacts (Xie et al. 2020). In this study, we conducted a Raman spectroscopy analysis on several samples of M-S4 shocked basalt (maskelynite-bearing from solid state shock pressures and not M-S5 through M-S7 in which labradorite is melted) collected from Lonar crater to identify maskelynite phenocrysts, contributing to our understanding of the crater's geology and the processes involved in maskelynite formation. The presence of maskelynite is an indicator of an intense shock event (Wright et al. 2011; Jaret et al. 2015). Method The method prepared thin M-S4 sample sections for Raman spectroscopy. Raman spectra used a red excitation laser (785 nm), 20X objective lens, 10 s exposure time, and 10% laser power. Spectra were obtained from various 30-45 micron maskelynite phenocrysts within M-S4 samples, while smaller needles were ignored. Baselines were subtracted, and an average Raman spectrum was generated by combining 10 individual spectra. The ~570 cm-1 peak is attributed to maskelynite. (Fritz et al. 2005; Kanemaru, et al. 2020). Discussion The feature at 576 cm-1 on the averaged Raman spectrum of Lonar maskelynite in basalts shocked ~20-40 GPa is particularly noteworthy (Fig.1). The presence of maskelynite in FTIR images of shocked soil from Lonar has been shown by Wright and Michalski (2024). Figures 4 and 9 of Wright et al. (2011) investigated the TIR emission spectrum of Lonar maskelynite. Figure 1. The average Raman spectrum of phenocrysts of maskelynite in MS-4 Lonar samples. The study connects Lonar crater's maskelynite to Martian meteorites, enhancing understanding of meteorite impacts on Mars' mineral composition and geologic history (Fritz et al. 2005; El Goresy et al. 2013). The findings link Lonar crater's maskelynite to Martian meteorites, providing vital insights into meteorite impacts' effects on Mars' mineral composition and geologic history. Conclusion Lonar crater is a great analog for studying Martian surface materials and processes due to its similarities with Mars' impact craters. This study successfully characterized maskelynite phenocrysts within M-S4 Lonar crater samples using Raman spectroscopy (Xie et al. 2021). The average Raman spectra offer crucial insights into the composition and formation of maskelynite. The research highlights Raman spectroscopy's significance as a dependable method for mineral analysis in impact-related samples, with potential applications at meteorite impact sites globally.

Bukit Bunuh is the most popular area of suspected meteorite impact crater. In the history of meteorite impact hitting the earth, Bukit Bunuh has complex crater of a rebound zone of positive magnetic anomaly value. This study area was located at Lenggong, Perak of peninsular Malaysia. The crater rim extended 5 km outwards with a clear subdued zone and immediately surround by a positive magnetic residual crater rim zone. A recent study was done to enhance the magnetic interpretation towards meteorite impact crater on this study area. The result obtained is being correlated with boreholes data to determine the range of local magnetic value. For the magnetic survey, the equipment used is Geometric G-856 Proton Precision magnetometers with the aids of other tools such as compass and GPS. In advance, the using of proton precision magnetometer causes it able in measures the magnetic fields separately within interval of second. Also, 18 boreholes are accumulated at study area to enhance the interpretation. The additional boreholes data had successfully described the structure of the impact crater at Bukit Bunuh in detailed where it is an eroded impact crater. Correlations with borehole records enlighten the results acquired from magnetic methods to be more reliable. A better insight of magnetic interpretation of Bukit Bunuh impact crater was done with the aid of geotechnical methods.

Sedimentary signatures and processes during marine bolide impacts: a review

The Xiuyan impact crater with a rim‐rim diameter of 1.8 km is located at northern hills in the Liaodong peninsula, Liaoning province, China, which is well reserved and confirmed by evidences from different sources to be a meteorite impact crater. A special geophysical field formed from the meteorite impact and subsequent deposit at the crater makes different medium velocity and density between inside and outside of the crater. In the project, velocity structures, stratum structures and whole configuration of the crater are gotten using the differences of seismic velocity and wave impedance from the combined exploration of reflection and refraction. Based on the reflection features of strata, the crater body formed by the direct impact has a diameter about 1.8 km and a depth about 800 m, and the depth affected by the impact is about 1.4 km. The crater structure is divided into 3 parts, slow deposition area, rapid deposition area and affected area. According to the seismic velocity features, the velocity at the crater center reaches 7.0 km/s at the depth of 800 m. The 7.0 km/s isoline is consistent with the crater configuration, but the velocity reaches 7.0 km/s at the depth of 500~600 m in the edge of the crater. The structure of the crater body and the physical property of rocks conform further that the Xiuyan crater is originated from meteorite impact.

Water diffusion into silica glass at a low temperature under high water vapor pressure

Homogeneous, dense glass bodies (both irregular and splash form) with high silica contents (∼67% SiO2) occur in the vicinity of Lonar Crater, India. Their lack of microlites and mineral remnants and their uniform chemical composition virtually preclude a volcanic origin. They are similar to tektites reported in the literature. While such a close association of tektite‐like bodies with impact craters is already known (Aouelloul Crater, Mauritania; Zhamanshin Crater, U.S.S.R.), the tektite‐like bodies at Lonar Crater are unique in that they occur in an essentially basaltic terrain. Our geochemical data are consistent with these high silica glass bodies being impact melt products of two‐thirds basalt and one‐third local intertrappean sediment (chert). The tektite‐like bodies of the impact craters Lonar, Zhamanshin, and Aouelloul are generally similar. Strong terrestrial geochemical signatures reflect the target rock REE patterns and abundance ratios and demonstrate their terrestrial origin resulting from meteorite impact, as has been suggested by earlier workers.

The shock wave resulting from a meteorite impact may be considered one of the basic tenets for the Cretaceous/Tertiary extinction [1],[2]. We can find several impact craters on the present earth where we find shock-wave deformation textures and high-pressure minerals formed by shock-wave effects. Especially, stishovite is one of the best known shock products in nature [3]. Diaplectic glasses transformed from mineral crystals by shock metamorphism are also very interesting shock metamorphic materials. Tschermak [4],[5] observed high-density glass of plagioclase composition in the Shergotty basaltic achondrite and named it Maskelynite. The name diaplectic glass was also introduced for such amorphous materials from Ries crater by Chao [3] and Engelhart and Stoffler [6]. Initial investigations of natural diaplectic glasses from meteorites and meteorite crater rocks were begun by Duke [7], Bunch et al. [8], and Stoflfler [9]. They reported that diaplectic plagioclase glasses showed higher refractive index than fused plagioclase glasses. The natural diaplectic quartz glasses also show higher density or refractive index than those of fused SiO2 glass [10],[11]. However, the number of impact craters on the present earth and the amount of shock-wave-derived material that we can investigate are very limited because of the large erosion effects on the earth’s surface. Therefore, it is difficult to estimate the scale of impact pressure and shock effect correctly. On the other hand, shock compression experiments have been extensively carried out for various minerals [12],[13].

In this paper, we reveal the feasibility of obtaining laboratory craters to investigate planetary events such as meteorite craters. Experiments were performed by using 0.44-mum laser beam with energy of les15 J in 350 ps (full-width at half-maximum) on aluminum targets. We obtain simple and complex craters similar in contour that are formed due to large meteorite impacts on the terrestrial surface. Simulations performed with the 2-D radiation hydrodynamic code MULTI help in understanding the origin of the experimentally observed central uplift of complex craters.

A recent paper in the JGS (Wall et al . 2008) presented a reassessment of seismic data, predicated on the assumption that the structure known as the Silverpit Crater was formed by a meteorite impact (Stewart & Allen 2002). This speculative hypothesis is merely based on a perceived similarity between the morphology of the Silverpit crater and impact craters, and has no scientific support. Stewart & Allen (2002) dated the geological event that formed the circular faults mapped at the top Chalk level by taking the lowest seismic reflector not affected by the faulting (apart from minor accommodation) to represent the latest date before which the faulting must have occurred. The unjustified assertion made now is that all coherent seismic events below the reflector CF (Wall et al . 2008, fig. 5) and top Chalk are sea-bed multiples, in particular the package MU (Wall et al . 2008). However, the time interval between the possible sea-bed multiple (a strong peak just above the base of the sequence) and the primary from which it may have been derived (the trough picked as HA) decreases up dip. There is no indication from other published profiles of the area that the sea depth changes rapidly enough to cause such convergence; nor could it be due to a migration effect because the actual dips (about 4.5°) are too shallow. Furthermore, coherent reflectors on other profiles (Wall et al . 2008, fig. 8, to the ESE of the crater; fig. 4, to the NW of the crater; fig. 5b, to the right …

A catalog of crater dimensions that were compiled mostly from the new Apollo-based Lunar Topographic Orthophotomaps is presented in its entirety. Values of crater diameter, depth, rim height, flank width, circularity, and floor diameter (where applicable) are tabulated for a sample of 484 craters on the Moon and 22 craters on Earth. Systematic techniques of mensuration are detailed. The lunar craters range in size from 400 m to 300 km across and include primary impact craters of the main sequence, secondary impact craters, craterlets atop domes and cones, and dark-halo craters. The terrestrial craters are between 10 m and 22.5 km in diameter and were formed by meteorite impact.

Many lunar craters greater than 10 km in diam exhibit a variety of morphological characteristics which are not produced by meteorite impact or meteorite erosion. Most such craters are located in or near the margins of the maria. Although some could have resulted from processes such as cauldron resurgence, caldera formation, or ring dike emplacement, most have formed by modification of impact craters by endogenic processes including erosion by flowing lava, fissure volcanism, plutonism and uplift of crater floors along ring fractures of impact origin.

Impact cratering: The South American record—Part 2

Analyses and interpretation of magnetic and gravity fields data acquired at Bukit Bunuh, Lenggong, Perak, Malaysia have been carried out in this study. The objective is to identify the meteorite impact crater and possible rebound locations. This study was instigated by an archaeological investigation carried out by the Centre for Global Archaeological Research, Universiti Sains Malaysia. The investigation suggested evidences of shock metamorphisms (suevite breccia) and crater morphology at Bukit Bunuh in Lenggong area of northern Perak, Malaysia. To justify the occurrence of the impact crater, ground magnetic and gravity surveys were conducted first as regional study in the entire area, followed by detailed study at the suspected crater region. Data from both surveys were compiled and corrected. The residual magnetic data ranged between -272 nT and +134.2 nT, whereas the Bouguer gravity data were between -25 mGal and 120 mGal. Both the magnetic and gravity data were gridded and plotted for qualitative interpretation. It was found that low magnetic and gravity region, believed to be an impact crater which is now filled with sediments and surrounded by a highly magnetised shallow bedrock, exists at the mid-part of the study area. Other high magnetic and gravity key features located within the central regions are interpreted as rebounds. In conclusion, the impact structure was successfully modelled as a complex impact crater.