Mineralogy, petrology, chronology, and exposure history of the Chelyabinsk meteorite and parent body

Abstract

Three masses of the Chelyabinsk meteorite have been studied with a wide range of analytical techniques to understand the mineralogical variation and thermal history of the Chelyabinsk parent body. The samples exhibit little to no postentry oxidation via Mössbauer and Raman spectroscopy indicating their fresh character, but despite the rapid collection and care of handling some low levels of terrestrial contamination did nonetheless result. Detailed studies show three distinct lithologies, indicative of a genomict breccia. A light‐colored lithology is LL5 material that has experienced thermal metamorphism and subsequent shock at levels near S4. The second lithology is a shock‐darkened LL5 material in which the darkening is caused by melt and metal‐troilite veins along grain boundaries. The third lithology is an impact melt breccia that formed at high temperatures (~1600 °C), and it experienced rapid cooling and degassing of S2 gas. Portions of light and dark lithologies from Chel‐101, and the impact melt breccias (Chel‐102 and Chel‐103) were prepared and analyzed for Rb‐Sr, Sm‐Nd, and Ar‐Ar dating. When combined with results from other studies and chronometers, at least eight impact events (e.g., ~4.53 Ga, ~4.45 Ga, ~3.73 Ga, ~2.81 Ga, ~1.46 Ga, ~852 Ma, ~312 Ma, and ~27 Ma) are clearly identified for Chelyabinsk, indicating a complex history of impacts and heating events. Finally, noble gases yield young cosmic ray exposure ages, near 1 Ma. These young ages, together with the absence of measurable cosmogenic derived Sm and Cr, indicate that Chelyabinsk may have been derived from a recent breakup event on an NEO of LL chondrite composition.

The Stubenberg meteorite—An LL6 chondrite fragmental breccia recovered soon after precise prediction of the strewn field

“…Since no fragments of other petrologic type have been observed so far a classification as a LL6 breccia is appropriate. However, Stubenberg does not belong to the complicated breccias like Almahata Sitta (e.g., Bischoff et al 2010;Horstmann et al 2010;Goodrich et al 2014;Horstmann and Bischoff 2014) or to the complex regolith breccias among the L-and LL-group ordinary chondrites (Bischoff et al 1993(Bischoff et al , 2006(Bischoff et al , 2013aMetzler et al 2010Metzler et al , 2011 and is also different to the LL5-6 breccia Chelyabinsk (Bischoff et al 2013b;Righter et al 2015;Morlok et al 2017). This is consistent with the lack of solar wind implanted noble gases (Fig.…”

“…indicate that the chemical composition of Stubenberg is close to the composition of Chelyabinsk (Righter et al. ) and that the Stubenberg chondrite is not chemically anomalous.…”

“…; Righter et al. ). It can be concluded that no anomalies in elemental composition of the Stubenberg meteorite were detected compared with other LL chondrites.…”

Shock stage distribution of 2280 ordinary chondrites—Can bulk chondrites with a shock stage of S6 exist as individual rocks?

“…; Horstmann and Bischoff ; Righter et al. ; Morlok et al. ), where thousands of different pieces reached the Earth's surface, have shown that meteorites can break up in the atmosphere resulting in large meteorite showers.…”

The Chelyabinsk event

“…All three phases have identical composition. The dark lithology was produced by shock-darkening (Kohout et al 2014;Reddy et al 2014;Richter et al 2015). Its reflectance spectrum can mimic carbonaceous material.…”