Geological Society of America

5 Planetary Surface Processes

Thursday, 12 April 2018
8:00 AM - 12:00 PM
Room 300 C

MINERALOGICAL AMBIGUITY OF THE IMPACT EJECTA OF LONAR CRATER, INDIA

Paper number: 5-3
Program: Theme Sessions
Time: 8:40 AM – 9:00 AM

Authors

Arif M. Sikder Presenting Author
Center for Environmental Studies (CES), Richmond, VA
Saumitra Misra
University of Kwazulu-Natal, Durban
Horton Newsom
Institute of Meteoritics and Dept. of Earth and Planetary Sciences, Albuquerque, NM
Jose Brum
Olympus Scientific Solutions Americas, Waltham, MA
Tina Hill
Madison, WI
Xin-Chen Liu
Virginia Commonwealth University (VCU), Richmond, VA
Joseph B. McGee Turner
Department of Chemistry, Richmond, VA

Abstract

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 (70^o) 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.

Geological Society of America Abstracts with Programs. Vol. 50, No. 3

doi: 10.1130/abs/2018SE-313244

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