IS LONAR ASTROBLEME AN EXAMPLE OF COMETARY IMPACT?

摘要

Based on the physico-chemical parameters of the shock-induced throw-out and fall-out ejecta in and around the Lonar astrobleme in Buldana District, Maharashtra, an impact model has been envisaged employing SURFER software package. According to this model, Lonar crater is classified into one that has suffered both high strain rate and high-temperature effects. The peak shock pressure is estimated to be around 1000 kb (100 Gpa). Employing the "Equation of State curves" for basal tic material, the impact velocity is estimated to be around 10 km/sec. Lack of any magnetic anomaly, high-pressure polymorphs and Fe-Ni spherules within the crater suggests that the impacting body was considerably less dense of the order of 1.5 gm/cc. and volatile in nature. Absence of any undisturbed parent bedrock in drill cores at a crater depth of 537m and higher proportion of "Microbreccia" relative to "Coarser breccia" suggests that the Lonar crater was unusual in depth-diameter ratio. Such unusual feature is ascribed to the nature of the boride which was more in a plasma state rather than a solid object.