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A Meteorite Impact Crater and Astroblemes in India. Vk Lunar and Planetary Science XXXIII (2002) 1129.pdf A METEORITE IMPACT CRATER AND ASTROBLEMES IN INDIA. V. K. Nayak, Department of Applied Geology, University of Saugar, saugar-3 (M.P.), India. The details of a meteorite impact crater at Lonar hills an small central peak from the Landsat image (19°58´N : 76°31´E) and astroblemes at Ramgarh (Grieve et al., 1988). Balasundaram and Dube (1973) (25°20´N : 76°37´30²E) and Shiva in the Indian observed shear fracturing, granulation and anomalous subcontinent are furnished and their significant birefringence in quartz grain and concorded with features highlighted. Crawford’s (1972) suggestion of impact origin of Ramgarh. However, definitive meteoritic impact Lonar Impact Crater signatures are lacking and at present the structure More than three decades of researches of the Lonar should be considered as ‘Ramgarh Astrobleme’. It is crater I Buldhana District, Maharashtra State, have suggested that a well-planned multi-disciplinary effort confirmed its meteorite impact origin (Nayak, 1972; is imperative to resolve the origin of the Ramgarh Fredriksson et al., 1973a; Fudali et al., 1980). The Astrobleme and thus make a significant contribution Lonar crater, 1830 m diameter, 150 m deep with a to the Earth’s cratering history. shallow saline lake in the floor, is unique in being the only terrestrial impact crater in basalts of the Shiva Astrobleme Cretaceous-Eocene age. It provides the closest analog A potential KT impact scar at the India-Seychelles with the Moon’s craters (Fredriksson et al., 1973b; rift margin has been interpreted as ‘Shiva Crater’ Fredriksson et al., 1978; Schaal, 1976). The nature of (Chatterjee and Rudra, 1996). It is an oblong shaped target basaltic rocks, various degrees of shock structure, 600 km long, 450 km wide and 12 km deep metamorphic signatures, nature of shocked and within the Deccan Traps and the underlying unshocked basalts, macro and micro breccias, glass Precambrian granite. The impact interpretation of spherules and impactites have provided definitive Shiva is based on subsurface stratigraphy, geophysical evidences for impact origin of the Lonar crater data, Bombay offshore oilfield and associated alkaline (Kieffer et al., 1976). The characteristics shock intrusives within the Deccan Traps. The KT boundary metamorphic features are compared and correlated age of the Shiva structure was inferred from its with those of the lunar craters in a planetary context Deccan lava floor, Palaeocene age of the overlying (Nayak, 2001). Such a comparative exercise of the sediments, isotope dating (~65 Ma) of presumed melt Lonar crater with the lunar craters will not only help rocks and the Carlsberg rifting event. Besides, seismic to unravel the extra-terrestrial geoscientific mysteries reflection data and India-Seychelles plate of the planets but also the evolution of the solar reconstruction at 65Ma indicate a buried oblong shape system. impact structure of Phanerozoic age. The structure shows the morphology of a complex impact crater and Ramgarh Astrobleme basin, a district uplift as series of peaks, an annular A spectacular annular structure at Ramgarh in trough and a slumped rim. Chatterjee and Rudra Kota District, Rajasthan, covers an area of 16 sq km (1996) conjectured the oblong shape of the structure within the Late Proterozoic Bhander Group of rocks of as a result of an oblique impact of a speculated 40 km the Vindhyan Supergroup. It has an outer diameter of diameter meteorite on the western continental shelf of 4 kms depth to diameter ratio 0.05 and about 200 m India, in a SW-NE trajectory at about 65MA. The height of the rim from the surrounding plain. A raised significance of the synchronous and near antipodal rim, quaquaversal dips, somewhat inverted positions of the Shiva crater and the Chicxulub crater topography and uplifting of rocks have been reported. in the Yucatán Peninsula, Mexico, are highlighted. The origin of this enigmatic feature is still a debated Although, Chatterjee and Rudra (1996) have strongly subject. An appraisal of various views and suggestions argued an impact origin of the Shiva structure but proposed from time to time was presented (Nayak, definitive evidence of shock metamorphic signatures 1997). These are: meteorite impact, kimberlite and are lacking. At present, therefore, the Shiva structure carbonatite intrusions, tectonism, combined action of should be considered as ‘Shiva Astrobleme’. tectonic and volcanic activity, subsidence, cryptovolcanism and dome etc. These explanations for the formation of the Ramgarh structure are mainly based on its geological, geomorphological, lithostratigraphical and structural characteristic. Besides, Ramgarh has also been described in the Astronaut’s Guide as an impact crater with ring of Lunar and Planetary Science XXXIII (2002) 1129.pdf A Meteorite Impact Crater and Astroblemes In India. V. K. Nayak References [1] Nayak, V.K. (1972) EPSL, 14(1), 1–6. [2] Fredriksson, K. et al. (1973a) Science, 180, 862–864. [3] Fudali, R.F. et al. (1980) Moon and Planets, 23, 493–515. [4] Fredriksson, K. et al. (1973b) Moon, 7, 475–482. [5] Fredriksson K. et al. (1978) Smithson. Contrib. Earth Sci., 22, 1–13. [6] Schaal, R.B. (1976) M. S. Thesis, Univ. California, USA, 143 pp. [7] Kieffer, S.W. et al. (1976) Proc. LSC 7th, 1391–1412. [8] Nayak, V.K. (2001) 26th Symp. Antarct. Meteorites, NIPR, Tokyo, 104–106. [9] Nayak, V.K. (1997) 22th Symp. Antarct. Meteorites, NIPR, Tokyo, 143–148. [10] Grieve, R.A.F. et al. (1988) LPI Tech Rpt. 88-03, 89 pp. [11] Balasundaram, M.S. and Dube, A (1973) Nature, 242, 40. [12] Crawford, A.R. (1972) Nature, 237, 98. [13] Chatterjee, S. and Rudra, D.K. (1996) Mem. Queensland Museum, Australia, 39(3), 489–532. .
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