Reconnaissance survey of the Duolun ring structure in Inner Mongolia: Not an impact structure

Abstract

The Duolun basin, which is located in Inner Mongolia, China, has been proposed to be an impact structure with an apparent rim diameter of about 70, or even 170 km. The designation as an impact structure was based on its nearly circular topography, consisting of an annular moat that surrounds an inner hummocky region, and the widespread occurrences of various igneous rocks, polymict breccias, and deformed crustal rocks. Critical shock metamorphic evidence is not available to support the impact hypothesis. We conducted two independent reconnaissance field surveys to this area and studied the lithology both within and outside of the ring structure. We collected samples from all lithologies that might contain evidence of shock metamorphism as suggested by their locations, especially those sharing similar appearances with impact breccias, suevites, impact melt rocks, and shatter cones. Field investigation, together with thin-section examination, discovered that the suspected impact melt rocks are actually Early Cretaceous and Late Jurassic lava flows and pyroclastic deposits of rhyolitic to trachytic compositions, and the interpreted impact glass is typical volcanic glass. Petrographic analyses of all the samples reveal no indications for shock metamorphic overprint. All these lines of evidence suggest that the Duolun basin was not formed through impact cratering. The structural deformation and spatial distribution pattern of the igneous rocks suggest that the Duolun basin is most likely a Jurassic-Cretaceous complex rhyolite caldera system that has been partly filled with sediments forming an annular basin, followed by resurgent doming of the central area. HighlightsThe impact origin for the Duolun basin in Inner Mongolia is disproved. Rocks of presumed impact origin do not show a shock metamorphic overprint. Field investigations and petrographic analyses indicate a volcanic origin of the structure. Duolun may be a rhyolite caldera system that was active during the Jurassic and Cretaceous.

The de-industrialisation discourse and the loss of modern industrial heritage in the Arab world: Jordan as a case study

“…This research used a field reconnaissance level survey, which has widely been used in research (e.g. Dumitru and Cosma, 2015;Xu et al, 2017) and can also be referred to as "impact assessment" or "rapid inventory". Reconnaissance survey is different from the intensive survey, despite the fact that both of them involve the same process of documentation where sufficient data should be gathered to give a professional description of the physical appearance and condition of a site or structure.…”

“…This research used a field reconnaissance level survey, which has widely been used in research (e.g. Dumitru and Cosma, 2015; Xu et al. , 2017) and can also be referred to as “impact assessment” or “rapid inventory”.…”

Formation mechanism of the Lidang circular structure in the Guangxi Province

“…Referring to the spatial distribution and erosion extent of confirmed Earth impact craters, Hergarten and Kenkmann () estimated the theoretical number of various‐sized undiscovered impact craters on Earth’s surface. Employing their algorithm, we estimated that there should be more than 13 craters larger than 1 km in diameter still preserved on the surface of China (Xu XM et al, ). However, as mentioned above, so far only one crater has been identified in the geological record in China.…”

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