Itqiy: A study of noble gases and oxygen isotopes including its terrestrial age and a comparison with Zakłodzie

Abstract

Abstract-We report noble gas, oxygen isotope, 14C and lOBe data of Itqiy as well as noble gas, 14Cand lOBe results for Zaklodzie. Both samples have been recently classified as anomalous enstatite meteorites and have been compared in terms oftheir mineralogy and chemical composition.The composition of enstatite and kamacite and the occurrence of specific sulfide phases in Itqiy indicate it formed under similar reducing conditions to those postulated for enstatite chondrites. The new results now seem to point at a direct spatial link.The noble gas record of Itqiy exhibits the presence of a trapped subsolar component, which is diagnostic for petrologic types 4-6 among enstatite chondrites. The concentration of radiogenic 4He is very low in Itqiy and indicates a recent thermal event. Its 21Ne cosmic-ray exposure age is 30.1 ± 3.0 Ma and matches the most common age range of enstatite chondrites (mostly EL6 chondrites) but not that of Zaklodzie.Itqiy's isotopic composition of oxygen is in good agreement with that observed in Zaklodzie as well as those found in enstatite meteorites suggesting an origin from a common oxygen pool. The noble gas results, on the other hand, give reason to believe that the origin and evolution ofItqiy and Zaklodzie are not directly connected. Itqiy's terrestrial age of 5800 ± 500 years sheds crucial light on the uncertain circumstances of its recovery and proves that Itqiy is not a modem fall, whereas the 14Cresults from Zaklodzie suggest it hit Earth only recently.

The Zakłodzie enstatite meteorite: Mineralogy, petrology, origin, and classification

“…Patzer et al (2001) found that the contents of heavy noble gases in Zak≥odzie are different from those in enstatite chondrites except the unequilibrated ones. The calculated cosmic-ray exposure age for the Zak≥odzie meteorite is 55.3 ± 5.5 Ma and is similar to those typical of enstatite achondrites (Patzer et al 2002). The formation age of the meteorite, calculated as the time of concentration of 4 He, which is a product of radioactive decay of uranium and thorium, equals 2.1 Ga.…”

“…Such a process could have happened only at an early age stage of the formation of the solar system, taking into account the relatively low decay constant of the 26 Al nuclide: T 1/2 ≈ 720, 000 years. This hypotheses is supported by the 40 K-40 Ar age of the meteorite (Patzer et al 2002).…”

“…This event may have happened at ∼2.1 Ga, the age obtained by measuring the accumulation of 4 He from the radioactive decay of uranium and thorium isotopes (Patzer et al 2002). The heating and partial re-melting caused partial loss of radiogenic 4 He, which is more weakly bound in minerals than 40 Ar, what is the result of its different radiogenic origin.…”

“…One stone, weighing 8.68 kg and partly covered by fusion crust, was found. Based on 14 C data, which suggests a young terrestrial age of Zak≥odzie, Patzer et al (2002) defined the meteorite as a "recent fall. "…”

New chemical and physical data on keilite from the Zaklodzie enstatite achondrite

“…The latter interpretation does not allow assignment of Zakłodzie within the meteorite classifi cation system. Przylibski et al (2003Przylibski et al ( , 2005, based on detailed observation, interpretation, and discussion of textures and mineral compositions, proposed another hypothesis that explained the observed features better, including published results of isotopic age determinations (KAr dating and 4 He concentration time method) on the parent body (Patzer et al 2002). Przylibski et al (2005) classifi ed Zakłodzie as a primitive enstatite achondrite, and proposed that the stone represents a new group of meteorites, similar to the primitive achondrites: lodranites, winonaites, and acapulcoites defi ned previously.…”