Documentation of shock features in impactites from the Dhala impact structure, India

1,2Jayanta Kumar Pati,3Michael H. Poelchau,4,5Wolf Uwe Reimold,6,7Norihiro Nakamura,6Yutaro Kuriyama,8Anuj Kumar Singh
Meteoritics & Planetary Science (in Press) Link to Article []
1Department of Earth and Planetary Sciences, Nehru Science Centre, University of Allahabad, Allahabad, 211 002 India
2National Center of Experimental Mineralogy and Petrology, University of Allahabad, 14 Chatham Lines, Allahabad, 211 002 India
3Institute of Earth and Environmental Science‐Geology, Albert‐Ludwigs‐Universität Freiburg, Albertstraße 23‐B, D‐79104 Freiburg, Germany
4Museum für Naturkunde ‐ Leibniz Institute for Evolution and Biodiversity Science, Invalidenstraße 43, 10115 Berlin, Germany
5Laboratory of Geochronology, Instituto de Geociências, Universidade de Brasília, CEP 70910 900 Brasília, DF, Brazil
6Department of Earth Science, Tohoku University, 6‐3 Aoba, Aramaki, Sendai, 980‐8578 Japan
7Institute for Excellence in Higher Education, Tohoku University, 42 Kawauchi, Sendai, 980‐8576 Japan
8Department of Earth and Planetary Sciences, Nehru Science Centre, University of Allahabad, Allahabad, 211 002 India
Published by arrangement with John Wiley & Sons

The fundamental approach for the confirmation of any terrestrial meteorite impact structure is the identification of diagnostic shock metamorphic features, together with the physical and chemical characterization of impactites and target lithologies. However, for many of the approximately 200 confirmed impact structures known on Earth to date, multiple scale‐independent tell‐tale impact signatures have not been recorded. Especially some of the pre‐Paleozoic impact structures reported so far have yielded limited shock diagnostic evidence. The rocks of the Dhala structure in India, a deeply eroded Paleoproterozoic impact structure, exhibit a range of diagnostic shock features, and there is even evidence for traces of the impactor. This study provides a detailed look at shocked samples from the Dhala structure, and the shock metamorphic evidence recorded within them. It also includes a first report of shatter cones that form in the shock pressure range from ~2 to 30 GPa, data on feather features (FFs), crystallographic indexing of planar deformation features, first‐ever electron backscatter diffraction data for ballen quartz, and further analysis of shocked zircon. The discovery of FFs in quartz from a sample of the MCB‐10 drill core (497.50 m depth) provides a comparatively lower estimate of shock pressure (~7–10 GPa), whereas melting of a basement granitoid infers at least 50–60 GPa shock pressure. Thus, the Dhala impactites register a strongly heterogeneous shock pressure distribution between <2 and >60 GPa. The present comprehensive review of impact effects should lay to rest the nonimpact genesis of the Dhala structure proposed by some earlier workers from India.


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