¹Senthil Kumar Perumal, ¹J. Prasanna Lakshmi Kopisetti, ¹Krishna Nagula, ¹Rajeev Menon, ¹Sruthi Uppalapati, ²Keerthi Vallabaneni, ²Senthil Kumar Arumugam, ¹Mysaiah Dasari, ¹Seshunarayana, ¹Tangirala, Mrinal K. Sen
¹National Geophysical Research Institute, Council of Scientific & Industrial Research, Hyderabad, India
²National Remote Sensing Centre, Indian Space Research Organization, Hyderabad, India

Impact fragmentation is an energetic process that has affected all planetary bodies. To understand its effects in basalt, we studied Lonar Crater, which is a rare terrestrial simple impact crater in basalt and analogues to km-scale simple craters on Mars. The Lonar ejecta consists of basaltic fragments with sizes ranging from silt to boulder. The cumulative size and mass frequency distributions of these fragments show variation of power index for different size ranges, suggesting simple and complex fragmentation. The general shape of the fragments is compact, platy, bladed and elongated with an average edge angle of 100 degrees. The size distribution of cobble- to boulder-sized fragments is similar to the fracture spacing distribution in the upper crater wall, indicating the provenance of those large fragments. Its consistency with a theoretical spallation model suggests that the large fragments were ejected from near surface of the target, whereas the small fragments from deeper level. The petrophysical properties of the ejecta fragments reflect the geophysical heterogeneity in the target basalt that significantly reduced the original size of spall fragments. The presence of Fe/Mg phyllosilicates (smectites) both in the ejecta and wall indicates the role of impact in excavating the phyllosilicates from the interior of basaltic target affected by aqueous alteration. The seismic images reveal a thickness variation in the ejecta blanket, segregation of boulders, fractures and faults in the bedrock beneath the crater rim. The fracturing, fragmentation and fluvial degradation of Lonar Crater has important implications for Mars.

Reference
Perumal SK, Kopisetti JPL, Nagula K, Menon R, Uppalapati S, Vallabaneni K, Arumugam SK, Dasari M, Tangirala S, Sen MK (2014) Impact fragmentation of Lonar Crater, India: Implications for impact cratering processes in basalt. Journal of Geophysical Research: Planets (in Press)
Link to Article [DOI: 10.1002/2013JE004543]

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