Mathematics – Logic
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30r.591v&link_type=abstract
Meteoritics, vol. 30, no. 5, page 591
Mathematics
Logic
Astroblemes, Chykcha, Craters, Impact, Geologic History, Metamorphism, Shock
Scientific paper
1. There is a deep topographic depression in the Northern Taymyr (the basin of Chykcha R.), centered at lat=75 degrees 42'N and lon=97 degrees 48'E. Its geological setting is made up of Rf3-O1 basement (terrigene-carbonaceous rocks which had been intensively dislocated to form complex syncline + anticline structures of NE strike; this strata was intruded by Rf1, Rf2 and Pz3 gabbro-granitic complexes) and Mz-Cz sedimentary cover which is partially preserved in the depressions; Q4 sediments are also broadly widespread. 2. The Chykcha depression is a rounded crater-like basin ~ 6 km in diameter, with step (6-9 degrees) slopes, flat bottom and central mount ~1 km in diameter and ~ 30 m in height.The visible depth of the depression is up to 200-220 m in respect to its borders and table mount relics of paleogenic planation; its full depth in the basement, without N2Q2 filling (up to 100 m in thickness) is ~300-320 m. Detailed geophysical data is absent for the depression. 3. No intensive brecciation and fracturing has been found on the slopes of the depression, but the central mount is made up of chaotic mixture of target rock megabreccia and klippes. Together with the intensive brecciation, the cleavage fracturing of the rocks as well as flat and glisten faces of perfect cleavage in quartz are also observed; last two features are believed to be the macroscopic evidence of shock damage. Under the microscope, PF (along {1011} and {3253} mainly), and PDF (along {1013} and {1012} mainly) have been found in this quartz, interpreted as the traces of weak shock metamorphism at pressures ~3.5-7 GPa. No traces of shatter cones are present. 4. The crater-like morphology and a clear superimposed position of the depression as well as megabreccia body and the traces of shock metamorphism indicate this basin to be a complex impact crater ~6 km in diameter, with the central mount. The parameters of the Chykcha impact event are estimated to be the next: energy of impact ~1,060 Mt TNT; mass of projectile ~14.5 Mt and its diameter ~150 m (iron variant) or ~200 m (chondrite variant); penetration into the target - up to 300 m; shock wave attenuation (pressure vs. distance under the point of impact), GPa/km: 100/0.47; 60/0.57; 30/0.73; 10/1.11; 5/1.43; 1/2.6. Next zones can also be estimated (depth under the point of impact): of ballistic excavation - ~430 m; of turbulent flow (the future bottom of crater) - ~770 m; of under-crater plastic flow and allogenic replacement - ~2,500 m. Due to the level of shock metamorphism in the central mount one can conclude that all the crater's impact fill was eroded and that the paleosurface of target was at least 300 m above the present level of planation. 5. The age of the Chykcha event is
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