¹P.G.Brown et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13368]
¹Department of Physics and Astronomy, University of Western Ontario, London, Ontario, N6A 3K7 Canada
²Centre for Planetary Science and Exploration, University of Western Ontario, London, Ontario, N6A 5B7 Canada
Published by arrangement with John Wiley & Sons

The Hamburg (H4) meteorite fell on 17 January 2018 at 01:08 UT approximately 10 km north of Ann Arbor, Michigan. More than two dozen fragments totaling under 1 kg were recovered, primarily from frozen lake surfaces. The fireball initial velocity was 15.83 ± 0.05 km s⁻¹, based on four independent records showing the fireball above 50 km altitude. The radiant had a zenith angle of 66.14 ± 0.29° and an azimuth of 121.56 ± 1.2°. The resulting low inclination (<1°) Apollo‐type orbit has a large aphelion distance and Tisserand value relative to Jupiter (T_j) of ~3. Two major flares dominate the energy deposition profile, centered at 24.1 and 21.7 km altitude, respectively, under dynamic pressures of 5–7 MPa. The Geostationary Lightning Mapper on the Geostationary Operational Environmental Satellite‐16 also detected the two main flares and their relative timing and peak flux agree with the video‐derived brightness profile. Our preferred total energy for the Hamburg fireball is 2–7 T TNT (8.4–28 × 10⁹ J), which corresponds to a likely initial mass in the range of 60–225 kg or diameter between 0.3 and 0.5 m. Based on the model of Granvik et al. (2018), the meteorite originated in an escape route from the mid to outer asteroid belt. Hamburg is the 14th known H chondrite with an instrumentally derived preatmospheric orbit, half of which have small (<5°) inclinations making connection with (6) Hebe problematic. A definitive parent body consistent with all 14 known H chondrite orbits remains elusive.

^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 [https://doi.org/10.1111/maps.13369]
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.