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Xiuyan crater, China: Impact origin confirmed
Abstract and Figures
The well-preserved 1.8-km-diameter Xiuyan crater is located in the low mountain-hill region of the northern part of Liaodong
Peninsula of northern China. Recently, a 307-m-deep borehole at the centre of crater became available. After penetrating 107
m lacustrine sediments, a breccia lens about 188 m in thickness was encountered. The crater-fill breccia is deposits of rock
clasts and fragments more or less shock-metamorphosed. The features of geological structure and stratigraphic configuration
within the crater, shock-melted rocks, and PDFs in quartz found in the basement rocks close to the crater rim and in the crater-fill
breccia provide clear evidence for an impact origin of the Xiuyan crater.
KeywordsXiuyan crater-shock metamorphism-breccia-PDFs-glass
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... The rim crest and both sides of rim are mostly covered with weathering soil, eluvial and diluvial deposits up to several meters thick. A few spots with exposed basement rocks (mainly leucoleptite) emerge from the rim walls (Chen et al., 2010). The crater floor is covered with Quaternary lacustrine sediments, with organic-rich lacustrine sediments in the upper part and loose brecciated rock debris and shock breccia accumulation in the lower part. ...
... In the numerical simulation using the SEM, to ensure the accuracy of the simulation results, it is required that at least five Gauss-Lobatto-Legendre integration points be contained in each The sketch of geological profile of Luoquanli basin (Chen et al., 2010). ...
The basin effects alter the frequency content, amplitude and duration of seismic waves with different depth and shape basin. In this paper, we selected 2-D geophysical profiles spanning the Weihe Basin with large area and the Luoquanli Basin with small area. Based on the velocity structure data of the two geophysical profiles, 2-D finite element models were established to analyze the influences of the sedimentary layer in a broad basin and the basement geometry of a small basin on the basin effects using the spectral element method. The results showed that the sedimentary deposits in the basin could significantly amplify the ground motion, and the diffraction waves generated by the lateral inhomogeneity of the basin could prolong the duration of the ground motion. The highlight of this paper, our results showed that the amplification characteristics were controlled by the velocity mean in the vertical direction of sedimentary deposits ( v p < 4.5 km/s) for a broad basin with small depth-to-width ratio as Weihe Basin, while the amplification characteristics were dominated by basement geometry of the small basin with large depth-to-width ratio as Luoquanli Basin. In this study, a high-resolution 2-D geophysical refraction profile was directly used to construct a finite element model to study the basin effects, which provided a new method of studying the basin effects.
... , 即辽宁岫岩陨石坑 [4] . 作为一种广泛存在的宇宙地质构 造, 全球陨石坑分布的不均一性引起了科学界的关 注 [5] . ...
... A further question, however, is raised by the stratigraphic distribution of confirmed Earth impact craters (Xiao ZY et al., 2018), which clearly shows that there are some near-blank areas on Earth's continents, regions in which the number of confirmed Earth impact craters is exceptionally small, such as the territory of China. So far, only the Xiuyan crater in the Liaoning Province has been confirmed as an impact crater in China (Chen M, 2008;Chen M et al., 2010). ...
The Lidang circular structure in the center of the Guangxi Province is about 8 km in diameter. This structure appears as an abnormal shallow depression that has disturbed the rather harmonic regional joint systems. Its unique occurrence in the whole region, the circular morphology, negative topography, and the spatial distribution of interior and exterior strata are all consistent with those of impact craters that are formed by asteroidal or cometary collision. To test the impact hypothesis, we carried out both field investigation and remote sensing study of this structure. Regional geological history suggests that if the impact hypothesis were correct, the impact event should have occurred at or after the Early Permian. Field investigation found that the strata inside and outside the crater are dominated by parallel stacks of Lower and Upper Permian limestone that have various thicknesses and different mud contents. The layers of limestone within and outside the circular structure have identical attitudes; no structural disturbances were visible in the outcrops. Field investigations provide conclusive evidence against the impact cratering hypothesis. A high-resolution digital elevation model shows that the spatial distribution of rounded mountains within the structure is controlled by faint but continual extension of joints, suggesting that the crater interior has gone through a much higher degree of erosion. Therefore, regional joints that had once existed within the crater are preserved less well than exterior terrains, forming the abruptly disrupted circular depression. Differential erosion, as the possible formation mechanism of the Lidang structure, is consistent with the different mud contents found between the interior and exterior limestone. The circular outline of this structure may correspond to the shape of the original deposition basin. In conclusion, the Lidang circular structure is a polje formed by karstification, not an astrobleme.
Crater is a geologic structure in solid bodies (including the terrestrial planets, moons, and asteroids) formed by hyper-speed impact, and the impact process is extremely important to the formation and evolution of these celestial bodies. This paper presents a review of the studies on remote sensing observation, formation mechanism, and scientific application of craters. On the remote sensing study of craters, the topographic characteristics of the micro-craters, simple craters, complex craters, and impact basins are described; the related parameters in the morphological studies of craters are subsequently introduced, and the distribution characteristics of the minerals and rock types during the impact excavation process are analyzed; the methods of crater identification and the crater databases on the Moon, Mars, Ceres, and Vesta are summarized. On the studies of crater formation mechanism, the general formation process of the craters is firstly described, and then the most frequently used methods are presented, and the importance of the empirical equations is also elucidated. On the scientific applications of the craters, the principle and currently utilization of the planetary surface dating method with crater size-frequency distribution are firstly presented, and the applications, including modeling the lunar regolith formation and thickness derivation of both the regolith and basalt, are reviewed. Finally, the future prospects of the formation mechanism study of the craters are discussed.
Coesite embedded in silica glass in suevite from the Xiuyan crater has been studied by scanning and transmission electron microscopy to better understand the mechanisms at formation of coesite. Coesite grains in this study mainly occur as vein‐like aggregates (10–40 μm in width) and irregular aggregates (IAs; <40 μm in size). Both aggregate types are composed of subhedral to anhedral coesite crystals with random orientations. Most of the crystals are 100–1000 nm in size, and some display twinning. The shape, twinning, and random orientation of coesite crystals suggest rapid crystallization in amorphous silica that became supercooled. The center of vein‐like aggregates crystallized from localized silica melt within diaplectic silica glass, whereas the rim of vein‐like aggregates and IAs crystallized from diaplectic silica glass. The size and amount of coesite crystals in the vein‐like aggregate vary greatly from the rim to the center of such veins. Microstructures suggest that the crystals nucleated heterogeneously at the outer rim of the vein and nucleated homogeneously within the vein. IAs do not show any changes in size and amount of coesite crystals from the rim to core of such aggregates. Coesite crystals in IAs primarily nucleate heterogeneously in diaplectic silica glass. It can be concluded that vein‐like coesite aggregates are mainly formed by crystallization from silica melt, and irregular coesite aggregates should be formed by solid‐state transformation of diaplectic silica glass.
The 7 km-diameter Jeokjung–Chogye Basin in Hapcheon, southeastern Korean Peninsula, is well-known for its bowl-shaped geomorphology. Here we report the first direct evidence of impact cratering from this basin based our investigations on a 142 m-deep core. The lithological units could be divided into soil-channel sediments (0–6.2 m), lacustrine sediments with fine silt-clayey lamination (6.2–72 m), and impact breccia (72–142 m). We report for the first time, unique impact-driven metamorphic features, including shatter cones at 130 m and planar deformation features (PDFs) in quartz grains from the impact breccia. Based on the radiocarbon dates of charcoals in the lacustrine sediments, we estimate that the impact likely happened during the last glacial period, although further confirmation using other dating techniques is awaited. This relatively young crater provides a rare opportunity to reconstruct high-resolution paleoclimate changes recorded in laminated lacustrine sediments, and to investigate shock metamorphism in a location that experienced significant surficial weathering and erosion under a tropical–temperate climate.
Feldspar is the most abundant mineral in the Earth’s crust and is widely distributed in rocks. It is also one of the most common minerals in meteorites. Shock-metamorphic features in feldspar are widely used to calibrate the temperature and pressure of shock events and can also provide clues for searching for impact craters on Earth. In this study, shocked alkali feldspars in the lithic breccia and suevite from Xiuyan Impact Crater were investigated using polarizing optical microscopes, Raman spectroscopy and electron microprobes to better constrain the shock history of this crater. For this study, feldspar grains occurring in gneiss clasts in the impact breccia and four shock stages were identified, e.g., weakly shocked feldspar, moderately shocked feldspar, strongly shocked feldspar, and whole rock melting. According to the shock classification system for alkali feldspar and felsic rocks, we estimated the shock pressure (SP) and post-shock temperature (PST) histories of these gneiss clasts. Weakly shocked feldspars display irregular fractures and undulatory extinction, and their shock stage is F-S2, which indicates that SP and PST are from ~5 to ~14 GPa and ~100 °C, respectively. Moderately shocked feldspars show planar deformation features and are partially transformed into diaplectic glass, which indicates that the F-S5 shock stage of SP and PST is from ~32 to ~45 GPa and 300–900 °C. Strongly shocked feldspars that occur as vesicular glass indicate a shock stage of F-S6, and the SP and PST are 45–60 GPa and 900–1500 °C, respectively. The whole felsic rock melting occurs as mixed melt glass clast and belongs to the F-S7 stage, and SP and PST are >60 GPa and >1500 °C, respectively.
The Xiuyan structure is a well-preserved simple bowl-shaped crater in the northern part of the Liaodong Peninsula of northern China.
The occurrence of shock metamorphosed quartz is the most common
petrographic criterion for the identification of terrestrial impact
structures and lithologies. Its utility is due to its almost ubiquitous
occurrence in terrestrial rocks, its overall stability and the fact that
a variety of shock metamorphic effects, occurring over a range of shock
pressures, have been well documented. These shock effects have been
generally duplicated in shock recovery experiments and, thus, serve as
shock pressure barometers. After reviewing the general character of
shock effects in quartz, the differences between experimental and
natural shock events and their potential effects on the shock
metamorphism of quartz are explored. The short pulse lengths in
experiments may account for the difficulty in synthesizing the
high-pressure polymorphs, coesite and stishovite, compared to natural
occurrences. In addition, post-shock thermal effects are possible in
natural events, which can affect shock altered physical properties, such
as refractive index, and cause annealing of shock damage and
recrystallization. The orientations of planar microstructures, however,
are unaffected by post-impact thermal events, except if quartz is
recrystallized, and provide the best natural shock barometer in terms of
utility and occurrence. The nature of planar microstructures,
particularly planar deformation features (PDFs), is discussed in some
detail and a scheme of variations in orientations with shock pressure is
provided. The effect of post-impact events on PDFs is generally limited
to annealing of the original glass lamellae to produce decorated PDFs,
resulting from the exsolution of dissolved water during
recrystallization. Basal (0001) PDFs differ from other PDF orientations
in that they are multiple, mechanical Brazil twins, which are difficult
to detect if not partially annealed and decorated. The occurrence and
significance of shock metamorphosed quartz and its other phases (namely,
coesite, stishovite, diaplectic glass and lechatelierite) are discussed
for terrestrial impact structures in both crystalline (non-porous) and
sedimentary (porous) targets. The bulk of past studies have dealt with
crystalline targets, where variations in recorded shock pressure in
quartz have been used to constrain aspects of the cratering process and
to estimate crater dimensions at eroded structures. In sedimentary
targets, the effect of pore space results in an inhomogeneous
distribution in recorded shock pressure and temperature, which requires
a different classification scheme for the variation of recorded shock
compared to that in crystalline targets. This is discussed, along with
examples of variations in the relative abundances of planar
microstructures and their orientations, which are attributed to textural
variations in sedimentary target rocks. Examples of the shock
metamorphism of quartz in distal ejecta, such as at the K/T boundary,
and from nuclear explosions are illustrated and are equivalent to that
of known impact structures, except with respect to characteristics that
are due to long-term, post-shock thermal effects. Finally, the
differences between the deformation and phase transformation of quartz
by shock and by endogenic, tectonic and volcanic processes are
discussed. We confirm previous conclusions that they are completely
dissimilar in character, due to the vastly different physical conditions
and time scales typical for shock events, compared to tectonic and
volcanic events. Well-characterized and documented shock effects in
quartz are unequivocal indicators of impact in the natural environment.
The origin of the well-preserved, 1.13-km-diameter Pretoria Saltpan crater in South Africa has been debated throughout this century. The structure of this Pleistocene crater resembles that of other simple, bowl-shaped impact craters, but the presence of volcanic intrusive rocks along the crater rim has suggested a cryptovolcanic origin. In 1989 a drill core from the crater became available. The core was studied in detail to establish a paleoenvironmental record for the mid-latitudes of the Southern Hemisphere by analyzing the undisturbed crater sediments that had accumulated since formation of the crater, and to determine the origin of the crater. The discovery of shock-metamorphosed quartz and feldspar fragments, melt breccia and siderophile element-enriched glasses, and sulfide spherules in crater breccia deposits provides clear evidence for the impact origin of the Pretoria Saltpan crater.
Up to now, 176 meteorite impact craters have been found on the Earth. Among these craters, none of them lies in China. The
Xiuyan crater is located in the Liaodong Peninsula of China. This bowl-shaped crater has a diameter of 1.8 km and depth of
about 150 m. The impact-derived features include planar deformation features (PDFs) in quartz, shatter cones, impact breccia,
and radial valleys on the wall of rim. It is the first confirmed meteorite impact crater in China.
Two distinct types of shock-induced quartz microstructure in charnockitic target rocks and quartz veins of the Charlevoix impact structure are described. The dominant shock effects in the type 1 microstructure in charnockites at similar to 2-4 km from the centre of the structure are planar deformation features (PDFs) parallel to rhombohedral planes of quartz. The abundance of different sets of these PDFs indicates a high hydrostatic component of the shock wave-associated stress (similar to 10-15 GPa). Evidence of crystal-plastic deformation due to high deviatoric stresses is absent. In contrast, PDFs parallel to the basal plane are predominant in the type 2 microstructure developed in rocks at similar to 4-9 km from the centre of the structure, whereas rhombohedral PDFs are rare. This indicates a lower hydrostatic stress component (similar to 7-8 GPa), which correlates with a radial decrease in recorded peak shock pressure. The basal PDFs are revealed by transmission electron microscopy to represent mechanical Brazil twins, which record crystal-plastic deformation at high deviatoric stresses (McLaren et al., 1967). These findings imply that the deviatoric component of the shock wave-associated stress increases relative to the hydrostatic component with increasing distance from the centre of the impact structure. In the type 2 microstructure, numerous deformation bands, strong undulose extinction and cataclastic zones at the optical scale, as well as glide-dislocations and microcracks at the TEM scale, occur in association with basal PDFs, and are therefore also interpreted to be shock-induced. This is consistent with the observation that quartz from the outer part of the impact structure is devoid of similar features. Thus, the highly heterogeneous and localised glide-controlled deformation accompanied by mechanical twinning and microcracking recorded by the type 2 microstructure is suspected to be induced by the high deviatoric stresses and high loading rates during shock. Post-shock recovery is indicated in the type 1 microstructure by the actual microstructure of rhombohedral PDFs, dislocations in climb configuration and well-ordered low angle grain boundaries, as well as in the type 2 microstructure by the occurrence of small elongate subgrains with low angle grain boundaries paralleling low-index planes. This has probably taken place during annealing shortly after the impact event at quasi-static conditions and still sufficiently high post-shock temperatures, rather than during a separate regional thermal event.
The importance of impact cratering on terrestrial planets is obvious from the abundance of craters on their surfaces. On Earth, active geological processes rapidly obliterate the cratering record. To date only about 170 impact structures have been recognized on the Earth's surface. Mineralogical, petrographic, and geochemical criteria are used to identify the impact origin of such structures or related ejecta layers. The two most important criteria are the presence of shock metamorphic effects in mineral and rock inclusions in breccias and melt rocks, as well as the demonstration, by geochemical techniques, that these rocks contain a minor extraterrestrial component. There is a variety of macroscopic and microscopic shock metamorphic effects. The most important ones include the presence of planar deformation features in rock-forming minerals, high-pressure polymorphs (e.g. of coesite and stishovite from quartz, or diamond from graphite), diaplectic glass, and rock and mineral melts. These features have been studied by traditional methods involving the petrographic microscope, and more recently with a variety of instrumental techniques, including transmission electron microscopy, Raman spectroscopy, cathodoluminescence imaging and spectroscopy, and high-resolution X-ray computed tomography. Geochemical methods to detect an extraterrestrial component include measurements of the concentrations of siderophile elements, mainly of the platinum-group elements (PGEs), and, more recently, chromium and osmium isotopic studies. The latter two methods can provide confirmation that these elements are actually of meteoritic origin. The Cr isotopic method is also capable of providing information on the meteorite type. In impact studies there is now a trend towards the use of interdisciplinary and multi-technique approaches to solve open questions.
This handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures emphasizes terrestrial impact structures, field geology, and particularly the recognition and petrographic study of shock-metamorphic effects in terrestrial rocks. Individual chapters include: 1) Landscapes with Craters: Meteorite Impacts, Earth, and the Solar System; 2) Target Earth: Present, Past and Future; 3) Formation of Impact Craters; 4) Shock-Metamorphic Effects in Rocks and Minerals; 5) Shock-Metamorphosed Rocks (Impactities) in Impact Structures; 6) Impact Melts; 7) How to Find Impact Structures; and 8) What Next? Current Problems and Future Investigations.
Shock wave attenuation rate and formation of central uplifts are not precisely constrained for moderately sized complex impact structures. The distribution of shock metamorphism in drilled basement rocks from the 10.5-kilometer-diameter Bosumtwi crater, and results of numerical modeling of inelastic rock deformation and modification processes during uplift, constrained with petrographic data, allowed reconstruction of the pre-impact position of the drilled rocks and revealed a shock attenuation by approximately 5 gigapascals in the uppermost 200 meters of the central uplift. The proportion of shocked quartz grains and the average number of planar deformation feature sets per grain provide a sensitive indication of minor changes in shock pressure. The results further imply that for moderately sized craters the rise of the central uplift is dominated by brittle failure.
Shock effects in quartz, plagioclase, biotite, amphibole, and some accessory minerals have been observed in rocks subjected to various degrees of meta morphism by meteoritic impact. The shock features described are unique; they are never observed in rocks from normal geologic environments. Such features are described: 1) Multiple sets of closely spaced planar microstructures occur in quartz, plagioclase, and other rock-forming minerals. Those characteristic of shock consist of alternating platelets, with a range of reduced mean index of re fraction and birefringence; they con sist of platelets that have been partially or completely transformed to an amor phous phase. 2) Quartz and plagioclase are selec tively and completely transformed to silica glass and plagioclase glass in the solid state, whereas the associated mafic minerals remained crystalline. There is no reaction between adjacent minerals. 3) High-pressure polymorphs occur, such as coesite or stishovite. Coesite oc Curs exclusively within silica glass; it has not been observed as a reaction or breakdown product. 4) Nickel-iron spherules occur in the fused glass or impactites. 5) The occurrence of droplets of ilmenite, rutile, pseudobrookite, and baddaleyite in impactites indicates a temperature of formation exceeding 150 degrees C. 6) Dense glass occurs, similar in composition to bulk rock, in which iron oxide, such as fine particles of mag netite, is completely dissolved. All these features are characteristic of a process involving the rapid rise and fall of extremiiely high pressures and temperatures. Minerals and mineral as semblages experiencing such high strain rates and sudden changes of pressures and temperatures react and change in dependently to the bulk chemical com position, under nonequilibrium condi tions. Many aspects of shock features re quire careful study. Kink bands in biotite and deformation lamellae in quartz occur in tectonically deformed rocks. These features should be studied with great care in order to determine whether reduction in mean index of refraction and total birefringence along the planar structures have resulted from vitrification or phase transition; their presence is additional evidence in favor of a shock mechanism. Vitreous phases or glasses formed by shock also have many unique prop erties; they have not been studied by such methods as thermoluminescence, electron spin resonance, low-angle x ray diffraction, or infrared spectroscopy. Shock-fused glass of high density needs to be studied in detail in carefully con trolled laboratory conditions. Experimental shock-wave studies of the equation-of-state of single minerals and mineral assemblages, under care fully controlled conditions, must pre cede estimates of peak pressures and peak and residual temperatures of shocked natural mineral assemblages. Detailed petrographic and mineralogic studies, however, have provided useful and definitive criteria for characteriza tion of impact events. Such data should be of paramount importance in the study of samples brought back from Moon.