IDENTIFICATION OF LONSDALEITE IN THE EJECTA MELTS AND ITS IMPLICATION IN RESOLVING THE TARGET AND IMPACTOR DILEMMA IN THE FORMATION OF LONAR CRATER, INDIA

After decades of investigation, still there are dilemmas in ascertaining the type of impactor and the target rock that is involved in the formation of Lonar Crater. it is generally perceived that the impact occurred on the unaltered Basalt (~69 and 63 Ma), though the impact cratering occurred (less than 50,000 years) that is tens of million years after the formation of Deccan Trap and it is very likely that in the meantime the postulated target basalts were extensively weathered to soil and sediments.

Spectral analysis with Raman microscopy detected the presence of lonsdaleite, mostly associated with metallic microlites and also in augite or plagioclase inclusions of the ejecta melts. SEM EDS analysis also affirms the presence of a significant amount of carbon in some of the microlites embedded in the ejecta melts.

The detection of the lonsdaleite in the ejected impact melts of the Lonar Crater might be of great importance in resolving the dilemma of the impactor and target rock issue in the formation of the crater. If the target rocks were consisting totally of unaltered flood basalt then the source of the carbon in the impact melt will be very challenging to resolve, other than the type of impactor. On the contrary the presence of paleosols beneath the ejecta blanket are carbonate-rich and full of caliche, a very good source of carbon. In consequence the identification of lonsdaleite in the impact melts suggesting that the target rocks were probably clastic sedimentary sequences and that probably contributed the carbon in the ejecta plume for the formation lonsdaleite in the impact melts.