AN ANALYSIS OF THE MICROLITES OF IMPACT MELT GLASSES OF LONAR CRATER, INDIA

The only well-preserved terrestrial simple crater in flood basalts is the Lonar Crater of India. The crater is well studied and the classical morphological features were identified, but yet lacking in obvious shock metamorphic evidences and geochemical signature of the impact. Polished thin sections of the glass spherules collected from the ejecta blanket of the Lonar crater were prepared for petrographic analysis of the microlites, to assess further the type of extraterrestrial components and the fractionation of impactor and the target materials. Primarily microlites were mapped and analyzed with scanning electron microscope equipped with energy dispersive spectrum analyzer. Lastly elemental and isotopic analysis of the microlites and the different optical phases of the glass samples were analyzed by using Agilent 8900 ICP-MS Triple Quad, using Helium as a collision gas and ESI NWR 193 nm ArF eximer laser with 30um spot size. Present analysis of the microlites of the glass spherules collected from the ejecta rim was revealed the variability in the concentration of Cr (2.55~11.34 ppm), Mn (32.78 ~ 125.86 ppm), Co (3.1~5.93 ppm), Ni (2.24~ 7.14 ppm), Cu (4.48 ~ 16.14 ppm), Zn (1.53 ~ 8.2 ppm), Fe (1024 ~ 6315 ppm), Sr (30.7~44.97 ppm) and Ba (176~228 ppm).

Chromium isotopic ratio of ⁵³Cr/⁵²Cr in the microlites sample varies between 0.61 to 0.9, due to the variable concentration of 53Cr. Whereas the host and altered materials of the ejecta rim shows significantly lower ratio of ⁵³Cr/⁵²Cr, i.e. 0.023 to 0.05. Study of the microlites embedded in impact melt glasses indicates that the ordinary L chondrite was the probable impactor, as revealed from Mn/Cr ratio (11.6~19.1) and Cr enrichment.