Critical comment on Aneeshkumar, V. et al., 2022, Lithos 426–427, 106779, Meteorite impact at Ramgarh, India
- Autor(en)
- W. U. Reimold, L. Ferrière, J. K. Pati, N. Hauser, C. Koeberl
- Abstrakt
The authors of this article (Aneeshkumar et al., 2022) claim to have identified shock metamorphic features, as well as evidence for the presence of an extraterrestrial component, in samples of metasedimentary target rocks from the Ramgarh impact structure (India). They also present zircon U-Pb isotopic data that supposedly bracket the age of the impact event between ~528 and 395 Ma. We critically assess these observations and conclusions. Based on established criteria for the recognition of shock effects in quartz, none of the allegedly shocked grains shows proper textural evidence of shock metamorphism. The purported enrichment of the target rocks in Cr, Ni, and Cu is not compared against concentrations of these elements in typical supracrustal rocks from the region around Ramgarh and, in general, is negligible in comparison to other crustal rocks. The reported data do not provide any evidence for the presence of a meteoritic component. The interpretation that this minor enrichment indicates a contribution from an impactor (suggested to be some “differentiated achondrite”) contradicts the established understanding of chemical and physical processes during impact. Target rocks such as those analyzed by Aneeshkumar et al. (2022) do not show extraterrestrial contamination, because even if samples were shocked, this would not affect their original chemical nature. Contamination from a meteoritic projectile at any known impact structure exists only in impact melt rock or melt-bearing suevitic impact breccia, which – to date – have not been described from Ramgarh. The reported U-Pb geochronological data do neither indicate an impact age nor do they provide evidence of shock deformation in zircon, or from highly shocked zircon, such as FRIGN zircon, grains. The authors describe magmatic and metamorphic zircon – which is unrelated to the impact event. The impact age would have to be obtained from authigenic zircon (or other datable minerals) crystallized from impact melt, or from highly shocked zircon, such as FRIGN zircon, grains. Thus, the meaning of the ~528–395 Ma age range reported in Aneeshkumar et al. (2022), in our opinion, remains unresolved, but it does not constrain the age of the impact event.
- Organisation(en)
- Department für Lithosphärenforschung
- Externe Organisation(en)
- Universidade de Brasília, Naturhistorisches Museum Wien (NHM), University of Allahabad
- Journal
- Lithos
- Band
- 438-439
- ISSN
- 0024-4937
- DOI
- https://doi.org/10.1016/j.lithos.2022.106971
- Publikationsdatum
- 02-2023
- Peer-reviewed
- Ja
- ÖFOS 2012
- 105105 Geochemie, 105127 Geochronologie
- Schlagwörter
- ASJC Scopus Sachgebiete
- Geology, Geochemistry and Petrology
- Link zum Portal
- https://ucrisportal.univie.ac.at/de/publications/c0d0c693-2035-4961-87a4-38cafcb05e37