Meteoritenalter und verwandte Probleme der Kosmochemie

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.

Section: Itqiy and Zaklodzie: A Comparison Of Noble Gas Recordsmentioning

confidence: 98%

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

Patzer¹,

Hill²,

Boynton³

et al. 2002

“…As a consequence, the calculated retention ages are lower than the actual crystallization ages and reflect the thermal history of the material. Since 4He is already mobilized at a few hundred degrees Celsius, the corresponding U,Th-4Her age is more easily modified or reset than the K-40Arr age of the same sample (Anders, 1964;Wanke, 1966).…”

Section: Gas Retention Agesmentioning

confidence: 99%

Noble gases in enstatite chondrites I: Exposure ages, pairing, and weathering effects

Patzer

Schultz

2001

Several E chondrites yield significantly lower 38Ar ages compared to those calculated from cosmogenic 3He and 21Ne. For these E chondrites, we suggest a reduction of cosmogenic 38Ar as a result of weathering. In order to prove the possible influence of terrestrial alteration on the cosmogenic noble gas record of E-chondritic material, we simulated terrestrial weathering in an experiment of 12 weeks duration. The treatment showed that a significant amount of cosmogenic 38Ar is lost on Earth by the influence of water.

“…Already in 1966 Wänke considered the possibility of Moon and Mars being parent bodies of certain meteorites (Wänke 1966); however, starting around 1980, more and more authors seriously considered the possibility that the SNC meteorites are from Mars (e.g., Wasson and Wetherill 1979;McSween and Stolper 1980;Wood and Ashwal 1981). Three observations were considered highly indicative:…”

Section: Introductionmentioning

confidence: 99%

Noble gases in mineral separates from three shergottites: Shergotty, Zagami, and EETA79001

Schwenzer¹,

Herrmann²,

Mohapatra

et al. 2007

Abstract-This study provides a complete data set of all five noble gases for bulk samples and mineral separates from three Martian shergottites: Shergotty (bulk, pyroxene, maskelynite), Zagami (bulk, pyroxene, maskelynite), and Elephant Moraine (EET) A79001, lithology A (bulk, pyroxene). We also give a compilation of all noble gas and nitrogen studies performed on these meteorites. Our mean values for cosmic-ray exposure ages from 3 He, 21 Ne, and 38 Ar are 2.48 Myr for Shergotty, 2.73 Myr for Zagami, and 0.65 Myr for EETA79001 lith. A. Serious loss of radiogenic 4 He due to shock is observed. Cosmogenic neon results for bulk samples from 13 Martian meteorites (new data and literature data) are used in addition to the mineral separates of this study in a new approach to explore evidence of solar cosmic-ray effects. While a contribution of this low-energy irradiation is strongly indicated for all of the shergottites, spallation Ne in Chassigny, Allan Hills (ALH) 84001, and the nakhlites is fully explained by galactic cosmic-ray spallation. Implanted Martian atmospheric gases are present in all mineral separates and the thermal release indicates a near-surface siting. We derive an estimate for the 40 Ar/ 36 Ar ratio of the Martian interior component by subtracting from measured Ar in the (K-poor) pyroxenes the (small) radiogenic component as well as the implanted atmospheric component as indicated from 129 Xe * excesses. Unless compromised by the presence of additional components, a high ratio of ~2000 is indicated for Martian interior argon, similar to that in the Martian atmosphere. Since much lower ratios have been inferred for Chassigny and ALH 84001, the result may indicate spatial and/or temporal variations of 40 Ar/ 36 Ar in the Martian mantle.