Identification of a meteoritic component using chromium isotopic composition of impact rocks from the Lonar impact structure, India

Abstract

The existence of mass‐independent chromium isotope variability of nucleosynthetic origin in meteorites and their components provides a means to investigate potential genetic relationship between meteorites and planetary bodies. Moreover, chromium abundances are depleted in most surficial terrestrial rocks relative to chondrites such that Cr isotopes are a powerful tool to detect the contribution of various types of extra‐terrestrial material in terrestrial impactites. This approach can thus be used to constrain the nature of the bolide resulting in breccia and melt rocks in terrestrial impact structures. Here, we report the Cr isotope composition of impact rocks from the ~0.57 Ma Lonar crater (India), which is the best‐preserved impact structure excavated in basaltic target rocks. Results confirm the presence of a chondritic component in several bulk rock samples of up to 3%. The impactor that created the Lonar crater had a composition that was most likely similar to that of carbonaceous chondrites, possibly a CM‐type chondrite.

Chromium isotopic insights into the origin of chondrite parent bodies and the early terrestrial volatile depletion

“…CK > EC (Enstatite Chondrites) % RC (Rumuruti Chondrites) > OC (Ordinary Chondrites) (Go ¨pel et al, 2015;Mougel et al, 2018;Pedersen et al, 2019;Qin et al, 2010;Shukolyukov and Lugmair, 2006;Trinquier et al, 2007;Van Kooten et al, 2016;Zhu et al, 2021). These isotopic differences between chondrites have been compared to the composition of the Earth's mantle (Mougel et al 2018) to detect and identify the likely sources of the impact-related extraterrestrial materials included in terrestrial rocks (e.g., Koeberl et al, 2007;Magna et al, 2017;Mougel et al, 2017;Mougel et al, 2019;Schmitz et al, 2016;Trinquier et al, 2006) and to test magma ocean models for asteroids (e.g., Zhu et al, 2019bZhu et al, , 2020b. To date, the most 54 Cr-rich phases analyzed in chondrites are 10 s to 100 s of nanometer-size presolar spinel grains that can be concentrated in acid residues (e.g., Podosek et al, 1997;Rotaru et al, 1992) and have been identified by NanoSIMS (Dauphas et al, 2010;Nittler et al, 2018;Qin et al, 2011).…”

Numerical simulation of meteorite impact on basaltic lavas at Lonar Crater, India

“…The discovery of maskelynite in the moderately shocked basalt and glassy objects in the ejecta clasts of the Lonar crater [23] was an important criterion for establishing the meteoritic impact origin of this crater. Detailed petrography, geochemical and spectroscopic analyses of the rocks also corroborated an impact origin [10,17,24,25]. The occurrence of coesite, a high-pressure polymorph of quartz has also been reported from the crater [26,27].…”

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

“…These authors analyzed the impact melt rock and glass samples from Morokweng, Bosumtwi, Clearwater East, Lappajarvi, and Rochechouart impact structures and based on the excesses of 53 Cr relative to the terrestrial standard (and occasional correlations with siderophile abundances), they concluded that the impactors are related to ordinary chondrites. However, taking the advantage of improved precision on the less abundant and mass independently varying 54 Cr and a richer Cr isotope dataset for meteorite groups, recent studies (e.g., Foriel et al, 2013;Magna et al, 2017;Mougel et al, 2019;Trinquier et al, 2006) could improve the efficacy of the Cr isotope approach to reveal the source of impactors at the level of individual meteorite groups within the CC and NC reservoirs. Based on the combined 53 Cr-54 Cr analyses of the impactites, Foriel et al (2013), Magna et al (2017), andMougel et al (2019) identified a ureilite-like impactor at the El'gygytgyn structure, a CI chondrite-like impactor for the Zhamanshin structure, and a CM-chondrite-like projectile for the Lonar crater, respectively.…”