Mathematics – Logic
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p31a1701b&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P31A-1701
Mathematics
Logic
[5420] Planetary Sciences: Solid Surface Planets / Impact Phenomena, Cratering
Scientific paper
A fascinating controversy has been recently renewed about the origin of the Karakul depression in the Pamir (Tajikistan, 39°1'N, 73°27'E), about 4000 m above sea level. Based on the work of E. Gurov reporting breccia and shock features in minerals, the circular depression was mentioned in the Earth Impact Database as one of the largest complex craters, about 50 km in diameter. However, recent studies have suggested that the basin is actually a NW-SE extensional rift. We report the preliminary results of a new expedition in the Karakul area that successfully took place in June 2011. Different types of rocks have been observed, including metamorphosed sediments, granite, limestone, and rare occurrence. The granite appears to be the youngest rock predating the crater, with an age of 230-190 My2. The most exciting preliminary result is the finding of shatter cones in metamorphosed sediments in the northern part of the peninsula. Breccias (not necessary impact-breccia) occur as floats on the central island, and were also found in the northern part of the rim. Thin sections are in preparation at the time of writing, and the report on the search for shock features in granite and breccias will be presented at the conference. The age of the crater is unknown, but is necessarily younger than the India-Asia collision, 55 - 60 My ago. On the basis of the oldest sediments filling the depression, the crater has been tentatively attributed to Neogene, or Pliocene, and would be then younger than 23 My. Consequences of the formation of a large complex crater in the recent geological history of the Pamir have yet to be explored. In a context of elevated convergence rate and rapid exhumation, the site offers the possibility to investigate the possible interactions between impact cratering and tectonic activity. The formation of a 50 km crater has considerable effects on the environment, at least at the regional scale, suggesting the search for such effects in the sediment record. Last but not least, if melt is present in some of our samples, the determination of precise age of the crater will be a priority, proving new constrains on the impact cratering rate in the recent history of the Earth.
Baratoux David
Baratoux L.
Bouley Sylvain
Bourdeille C.
Colas Francois
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