Popigai crater
The Popigai crater in Siberia, Russia is tied with Manicouagan Crater as the fourth largest verified impact crater on Earth.[1][2] A large bolide impact created the 100 kilometres (62 mi) diameter crater 35.7 ± 0.2 (2σ) million years ago during the late Eocene (Priabonian stage).[3][4] The crater is 1½ hours (by helicopter) from the outpost of Khatanga. It is designated by UNESCO as a Geopark, a site of special geological heritage.[5]
For decades the Popigai crater has fascinated paleontologists and geologists, but the entire area was completely off limits because of the diamonds and the mines constructed by gulag prisoners under Stalin; however, a major investigatory expedition was undertaken in 1997 (IPEX 1997) which greatly advanced understanding of the enigmatic structure.[5] The impactor in this event has been identified as either an 8 km (5.0 mi) diameter chondrite asteroid, or a 5 km (3.1 mi) diameter stony asteroid.
The shock pressures from the impact instantaneously transformed graphite in the ground into diamonds within a 13.6 km (8.5 mi) radius of the impact point. Diamonds are usually 0.5 to 2 mm (0.020 to 0.079 in) in diameter; a few exceptional specimens are 10 mm (0.39 in) in size. The diamonds not only inherit the tabular shape of the original graphite grains but they additionally preserve the original crystal's delicate striations.[5]
Popigai is the best example yet of the formation of a crater of this type. Three other craters are larger, but they are either buried (Chicxulub), strongly deformed (Sudbury), or deformed and severely eroded (Vredefort).
There is a small possibility that Popigai impact crater formed simultaneous with the approximately 35 million year old Chesapeake Bay and Toms Canyon impact craters.[3]
[edit] References
- ^ "Popigai". Earth Impact Database. University of New Brunswick. http://www.passc.net/EarthImpactDatabase/popigai.html. Retrieved 2008-12-30.
- ^ Masaitis, Victor L. (2003). Popigai Crater: General Geology. Springer. pp. 81–85. ISBN 9783540435174. http://books.google.com/?id=mLfsNALR19oC&pg=PA109&dq=Popigai+Chesapeake+age.
- ^ a b Deutsch, Alexander; Christian Koeberl (2006). "Establishing the link between the Chesapeake Bay impact structure and the North American tektite strewn field: The Sr-Nd isotopic evidence". Meteoritics & Planetary Science 41 (5): 689–703. doi:10.1111/j.1945-5100.2006.tb00985.x. http://www.ingentaconnect.com-content-arizona-maps-2006-00000041-00000005-art00004. Retrieved 2008-06-16.
- ^ Armstrong, Richard; S. Vishnevsky & C. Koeberl (2003). U-Pb Analysis of zircons from the Popigai impact structure, Russia: First Results. Springer. pp. 99–116. ISBN 9783540435174. http://books.google.com/?id=mLfsNALR19oC&pg=PA109&dq=Popigai+Chesapeake+age.
- ^ a b c Deutsch, Alexander; V.L. Masaitis, F. Langenhorst & R.A.F. Grieve (2000). "Popigai, Siberia—well preserved giant impact structure, national treasury, and world's geological heritage". Episodes 23 (1): 3–12. http://www.episodes.org/backissues/231/03-11%20Deutsch.pdf. Retrieved 2008-06-16.
[edit] External links
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