Zhamanshin astrobleme provides evidence for carbonaceous chondrite and post-impact exchange between ejecta and Earth’s atmosphere

Abstract

Chemical fingerprints of impacts are usually compromised by extreme conditions in the impact plume, and the contribution of projectile matter to impactites does not often exceed a fraction of per cent. Here we use chromium and oxygen isotopes to identify the impactor and impact-plume processes for Zhamanshin astrobleme, Kazakhstan. ε54Cr values up to 1.54 in irghizites, part of the fallback ejecta, represent the 54Cr-rich extremity of the Solar System range and suggest a CI-like chondrite impactor. Δ17O values as low as −0.22‰ in irghizites, however, are incompatible with a CI-like impactor. We suggest that the observed 17O depletion in irghizites relative to the terrestrial range is caused by partial isotope exchange with atmospheric oxygen (Δ17O = −0.47‰) following material ejection. In contrast, combined Δ17O–ε54Cr data for central European tektites (distal ejecta) fall into the terrestrial range and neither impactor fingerprint nor oxygen isotope exchange with the atmosphere are indicated.

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

“…This estimate of 1–3% of chondritic fraction in the Lonar target matrix is consistent with the amount of impactor material found in impact rocks from other craters (e.g., Zhamanshin, Magna et al. ; Morokweng, Koeberl and Reimold ) or impact layers (e.g., Wittenoom layer, Simonson et al. ; Grænsesø layer, Mougel et al.…”

“…Therefore, in contrast to previous speculation concerning the nature of the Lonar impactor, the Cr isotopes show that a carbonaceous chondrite object must be involved with the origin of the Lonar crater. The absence of Cr enrichments in bulk impactites, despite the input of chondritic material, is nonintuitive because the contribution of chondritic material would expect to be reflected in the Cr abundances as well, as shown by the correlation between e 54 Cr and 1/Cr in KT ejecta samples presented in Trinquier et al (2006) or by coupled Cr enrichments and isotopic anomalies in impact glasses from the Zhamanshin impact structure (Jon a sov a et al 2016; Magna et al 2017). This is, however, not systematic; other studies like Foriel et al (2013) and Mougel et al (2017) have reported Cr isotopic anomalies in impactites without being correlated with siderophile element enrichments.…”

“…Koeberl et al 2002). This approach has been successfully used for the identification of the impactors involved in the formation of the Morokweng, Bosumtwi, Clearwater East, Lappaj€ arvi, El'gygytgyn, and Rochechouart Foriel et al 2013) impact structures as well as for ejecta layers (e.g., Lugmair and Shukolyukov 1998;Kyte et al 2003Kyte et al , 2011Trinquier et al 2006;Quitt e et al 2007;Simonson et al 2009;Magna et al 2017;Mougel et al 2017). Therefore, we took advantage of this sensitive method to investigate the type of chondrite involved in the formation of the Lonar crater.…”

Pantasma: Evidence for a Pleistocene circa 14 km diameter impact crater in Nicaragua

“…; Magna et al. ). The intermediary ε 54 Cr of breccia sample P5B (ε 54 Cr = −0.11± 0.07) between terrestrial rocks (0.02 < ε 54 Cr < 0.19) and ordinary chondrites (ε 54 Cr = −0.39 ± 0.12; Göpel et al.…”

“…The second diagnostic evidence for impact is the presence of an extraterrestrial Cr isotopic signal in the polymict breccia sample P5B, suggesting an ordinary chondrite impactor. Since the Cr isotopic composition of each meteorite group is distinct from the Earth (with the exception of enstatite chondrites; Mougel et al 2018), and because Cr is much more abundant in chondrites than in the terrestrial crust, the presence of non-massdependent Cr isotopic variations in terrestrial rocks is a very robust indicator of extraterrestrial material (e.g., Shukolyukov and Lugmair 1998;Koeberl et al 2007b;Trinquier et al 2006;Moynier et al 2009;Kyte et al 2011;Foriel et al 2013;Mougel et al 2017;Magna et al 2017). The intermediary e 54 Cr of breccia sample P5B (e 54 Cr = À0.11AE 0.07) between terrestrial rocks (0.02 < Fig.…”