Chromium isotopes identify the extraterrestrial component in impactites from Dhala impact structure, India

1,2Aryavart ANAND,3Anuj Kumar SINGH,1Klaus MEZGER,3.4Jayanta Kumar PATI
Meteoritics & Planetary Science (in Press) Open Access Link to Article [doi: 10.1111/maps.139821Ó2023]
1Institut für Geologie, Universität Bern, Bern, Switzerland
2Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany
3Department of Earth and Planetary Sciences, Nehru Science Centre, University of Allahabad, Prayagraj, India
4National Centre of Experimental Mineralogy and Petrology, University of Allahabad, Prayagraj, India
Published by arrangement with John Wiley & Sons

The Dhala structure in north-central India is a confirmed complex impactstructure of Paleoproterozoic age. The presence of an extraterrestrial component inimpactites from the Dhala structure was recognized by geochemical analyses of highlysiderophile elements and Os isotopic compositions; however, the impactor type hasremained unidentified. This study uses Cr isotope systematics to identify the type ofprojectile involved in the formation of the Dhala structure. Unlike the composition ofsiderophile elements (e.g., Ni, Cr, Co, and platinum group elements) and their inter-elementratios that may get compromised due to the extreme energy generated during an impact, Crisotopes retain the distinct composition of the impactor. The distincte54Cr value of0.310.09 for a Dhala impact melt breccia sample (D6-57) indicates inheritance from animpactor originating within the non-carbonaceous reservoir, that is, the inner Solar System.Based on the Ni/Cr ratio, Os abundance, and Cr isotopic composition of the samples, theimpactor is constrained to be of ureilite type. Binary mixing calculations also indicatecontamination of the target rock by 0.1–0.3 wt% of material from a ureilite-like impactor.Together with the previously identified impactors that formed El’gygytgyn, Zhamanshin,and Lonar impact structures, the Cr isotopic compositions of the Dhala impactites arguefor a much more diverse source of the objects that collided with the Earth over itsgeological history than has been supposed previously.


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