Asteroids, Comets, Meteors (2012) 6037.pdf KARAKUL DEPRESSION, TADJIKISATAN – A YOUNG IMPACT CRATER ? D. Baratoux1, S. Bouley2,9, L. Baratoux3, D., F. Colas2, F., J.L. Dauvergne4, J. Vaubaillon2, H. Chennaoui-Aoudjehane5, A. Jambon6, J. Gattac- ceca7, A. Losiak8, C. Bourdeille9, A. Jullien9, K. Ibadinov10.1Université de Toulouse, UPS-OMP; IRAP; Toulouse, France ([email protected]).2Observatoire de Paris, IMCCE, Paris, France.3Université de Toulouse, UPS- OMP; GET; Toulouse, France. 4Ciel et Espace, Paris, France. 5Hassan II University Casablanca Faculty of Sciences - Department of Earth Sciences. 6Laboratoire ISTeP, Université Pierre et Marie Curie, Paris, France. 7Cerege, Aix- en-Provence, France. 8University of Vienna, Department of Lithospheric Research, Vienna, Austria. 9Uranoscope de France, Paris, France. 10Astrophysical Institute of Dushanbe, Tajikistan. Introduction: A fascinating controversy has been tures that evocate PFs or PDFs depending on their recently renewed about the origin of the Karakul de- spacing (Fig. 2). High-pressure silica phases in these pression in the Pamir (39°1’N, 73°27’E). The depres- samples are also searched with an approach combining sion lies 4000 m above sea level and at the northeast of Raman spectroscopy and cathodoluminescence6. the mountain range of Tajikistan and comprises an internally drained lake. Following the work of Eugene Gurov1,2 reporting breccia and shock features in miner- als, the circular fearture is mentioned in the Earth Im- pact Database3 as one of the largest complex craters, (50 km in diameter). Its age is unknown, but necessari- ly younger than the India-Asia collision, 55 – 60 My ago and has been tentatively attributed to Neogene, or Pliocene1,2. More recent studies have suggested that the basin is actually an extensional rift currently experi- 4,5 encing NW-SE transtensional deformation . These authors interpret the presence of a peninsula and an Fig. 2 - Closely spaced planar features in a quartz island at the center of the depression as a graben4,5. A grain evocating PDFs (XPL). new expedition took place in June 2011. The southern Exceptional twinning has been observed in calcite rim, the northern rim, the peninsula and the central grains (Fig. 3), with strong resemblance with observa- island were explored and sampled. tions reported for other impact structures in calcite7. Field observations: Different types of rocks have The conditions of formation of these twins will be ana- been observed: metamorphosed sediments, granite, lyzed from Electron Paramagnetic Resonnance8. limestone, and rare occurrence. The most exciting pre- liminary result is the finding of shatter cones in meta- morphosed sediments in the northern part of the penin- sula (Fig. 1). Breccias occur as floats on the central island, and were also found in the northern part of the rim. We could not find any evidence for normal faults and horst structure for the island and peninsula. Fig. 3 - Closely spaced twins observed in calcite(XPL). References: 1Gurov and Gurova (1993) Geolog- icheskii zhurnal, 6, 53-64. 2Gurov et al. (1993). XXIV Lunar Plan. Sci. Conf., 591-592. 3http://www.passc.net/EarthImpactDatabase. 4Amidon and Hynek (2010), Tectonics, TC5017. 5Robinson et al. (2004). Geol. Soc. of Am. Bull., 116, 953-73. Fig.1 - Shatter cones in metasediment (peninsula). 6Chennaoui-Aoudjehane et al. (2005) Meteor. Plan. Search for shock metamorphism: Thin sections Sc., 40, 967 – 979. 7Burt et al. (2005) Met. Plan. Sc., of granite and breccias have been examined under the 40, 297. 8Polanskey and Ahrens (1994), JGR, 99, microscope. A few quartz grains exhibit planar fea- 5621-5638. .