Geophysical survey of the proposed Tsenkher impact structure,Gobi Altai,Mongolia |
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| Authors: | Jens ORMÖ David GOMEZ‐ORTIZ Goro KOMATSU Togookhuu BAYARAA Shoovdor TSERENDUG |
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| Institution: | 1. Centro de Astrobiología (CSIC‐INTA), 28850 Torrejón de Ardoz, Spain;2. Departamento de Biologia y Geologia, Universidad Rey Juan Carlos, 28933?Móstoles, Spain;3. International Research School of Planetary Sciences, Università d’Annunzio, 65127 Pescara, Italy;4. Planetary Exploration Research Center, Chiba Institute of Technology, 2‐17‐1 Tsudanuma, Narashino‐shi, Chiba 275‐0016, Japan;5. Ulaanbaatar Astronomical Observatory, Research Center of Astronomy and Geophysics, Mongolian Academy of Sciences, P.O. Box 152, Ulaanbaatar, Mongolia;6. Department of Geomagnetism, Research Center of Astronomy and Geophysics, Mongolian Academy of Sciences, P.O. Box 152, Ulaanbaatar, Mongolia |
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| Abstract: | Abstract– We have performed forward magnetic and gravity modeling of data obtained during the 2007 expedition to the 3.7 km in diameter, circular, Tsenkher structure, Mongolia, in order to evaluate the cause of its formation. Extensive occurrences of brecciated rocks, mainly in the form of an ejecta blanket outside the elevated rim of the structure, support an explosive origin (e.g., cosmic impact, explosive volcanism). The host rocks in the area are mainly weakly magnetic, silica‐rich sandstones, and siltstones. A near absence of surface exposures of volcanic rocks makes any major volcanic structures (e.g., caldera) unlikely. Likewise, the magnetic models exclude any large, subsurface, intrusive body. This is supported by an 8 mGal gravity low over the structure indicating a subsurface low density body. Instead, the best fit is achieved for a bowl‐shaped structure with a slight central rise as expected for an impact crater of this size in mainly sedimentary target. The structure can be either root‐less (i.e., impact crater) or rooted with a narrow feeder dyke with relatively higher magnetic susceptibility and density (i.e., volcanic maar crater). The geophysical signature, the solitary appearance, the predominantly sedimentary setting, and the comparably large size of the Tsenkher structure favor the impact crater alternative. However, until mineralogical/geochemical evidence for an impact is presented, the maar alternative remains plausible although exceptional as it would make the Tsenkher structure one of the largest in the world in an unusual setting for maar craters. |
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