| 词条 | Morokweng crater |
| 释义 |
| name = Morokweng crater | other_name = Morokweng impact structure | photo = | photo_size = | photo_alt = | photo_caption = | map = South Africa | map_alt = | map_caption = Location of the crater in South Africa | map_size = | location = | label = | label_position = | coordinates = {{coord|-26.466667|23.533333|region:ZA_type:landmark|display=inline,title}} | coordinates_ref = | confidence = Confirmed | diameter = {{convert|70|km|mi|abbr=on}} | depth = | rise = | imp_size = | age = 145.0 ± 0.8 Ma Jurassic-Cretaceous boundary | exposed = No | drilled = Yes | bolide = LL chondrite | translation = | language = | pronunciation = | topo = | access = | country = {{RSA}} | state = | province = North West | district = | municipality = }} The Morokweng crater (or Morokweng impact structure) is an impact crater buried beneath the Kalahari Desert near the town of Morokweng in South Africa's North West province, close to the border with Botswana.[1] DescriptionThe crater, formed by an asteroid {{convert|5|to|10|km|mi|abbr=on}} in diameter, is at least about {{convert|70|km|mi|abbr=on}} in diameter and the age is estimated to be 145.0 ± 0.8 million years, placing it at the Jurassic–Cretaceous boundary. Discovered in 1994, it is not exposed at the surface, but has been mapped by magnetic and gravimetric surveys. Core samples have shown it to have been formed by the impact of an L chondrite asteroid.[2] In May, 2006, a group of scientists drilling into the site announced the discovery of a {{convert|25|cm|in|abbr=on}}-diameter fragment of the original asteroid at a depth of {{convert|770|m|ft|abbr=on}} below the surface, along with several much smaller pieces a few millimetres across at other depths. This discovery was unexpected, since previous drillings on large impact craters had not produced such fragments, and it was thought that the asteroid had been almost entirely vaporised.[3] Some of the fragments can be seen in the Antenna Wing of London's Science Museum. References1. ^{{Cite Earth Impact DB |name=Morokweng |accessdate=2017-10-09}} 2. ^{{cite_journal | title = Meteoric component in impact melt rocks from the Morokweng, South Africa, impact structure: An OS isotopic study | journal = Lunar and Planetary Science | volume = 31 |author1=Christian Koeberl |author2=Bernhard Peucker-Ehrenbrink |author3=Wolf Uwe Reimold | url = http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1595.pdf|format=PDF}} 3. ^{{cite journal | first = WD | last = Maier |author2=Andreoli MA |author3=McDonald I |author4=Higgins MD |author5=Boyce AJ |author6=Shukolyukov A |author7=Lugmair GW |author8=Ashwal LD |author9=Graser P |author10=Ripley EM |author11=Hart RJ | date = May 11, 2006 | title = Discovery of a 25-cm asteroid clast in the giant Morokweng impact crater, South Africa | journal = Nature | volume = 441 | issue = 7090 | pages = 203–6 | pmid = 16688173 | doi = 10.1038/nature04751|bibcode = 2006Natur.441..203M }} Further reading
External links
7 : Impact craters of South Africa|Cretaceous impact craters|Jurassic impact craters|Late Jurassic Africa|Early Cretaceous Africa|Cretaceous South Africa|Jurassic South Africa |
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