MINERALOGICAL AMBIGUITY OF THE IMPACT EJECTA OF LONAR CRATER, INDIA
SIKDER, Arif M., Virginia Commonwealth University (VCU), Center for Environmental Studies (CES), Richmond, VA 23284, MISRA, Saumitra, Department of Geology, University of Kwazulu-Natal, Private Bag X54001, Durban, 4000, South Africa, HORTON, Newsom, University of New Mexico, Institute of Meteoritics and Dept. of Earth and Planetary Sciences, Albuquerque, NM 87131, BRUM, Jose, Olympus Scientific Solutions Americas, 48 Woerd Ave, Suite 105, Waltham, MA 02452, HILL, Tina R., Bruker AXS Inc., 5465 E. Cheryl Parkway, Madison, WY 53711, LIU, Xin-Chen, Center for Environmental Studies (CES), Virginia Commonwealth University (VCU), 1000 West Cary Street, Richmond, VA 23284 and TURNER, Joseph B. McGee, Virginia Commonwealth University (VCU), Department of Chemistry, 1001 West Main Street, Richmond, VA 23284
The comparatively young (50,000 years old) Lonar crater of India is presumably one of the two known terrestrial impact craters that emplaced about 65 million years old Deccan basalt. The impact cratering occurred tens of million years after the formation of the Deccan Basalt and it is very likely that in the meantime the postulated target basalts layers were extensively altered due to weathering.
Detailed mineralogical analysis of 6 (six) ejecta samples by XRD (using both Cu and Co source), SEM-EDS and micro-Raman revealed that the mineral assemblage of the ejecta primarily consists of andesine [(Na,Ca)(Si,Al)4O8], diopside [CaMgSi2O6], augite [(Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6], carbonates [calcite (CaCO3) and magnesite (MgCO3)]; along with trace amount of magnetite (Fe2O4), hematite (Fe2O3) and cowlesite [CaAl2Si3O106(H2O)], a low-silica zeolite formed due to low temperature (70o) alteration of low-silica rocks.
The prevalence of andesine presents some ambiguity in matching the ejecta with tholeiitic basaltic target and suggest that multiple phases of pre and post-impact alterations probably accountable for the present mineralogical assemblage. The impact cratering probably occurred on the weathered basaltic rocks that was depleted in certain metals and the zeolites probably developed due to post-impact hydrothermal alteration and finally climatic condition probably facilitated the calcification of the ejecta blanket and the preservation of the ejecta fallout.
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