Annama H chondrite-Mineralogy, physical properties, cosmic ray exposure, and parent body history

The fall of the Annama meteorite occurred early morning (local time) on April 19, 2014 on the Kola Peninsula (Russia). Based on mineralogy and physical properties, Annama is a typical H chondrite. It has a high Ar-Ar age of 4.4 Ga. Its cosmic ray exposure history is atypical as it is not part of the large group of H chondrites with a prominent 7-8 Ma peak in the exposure age histograms. Instead, its exposure age is within uncertainty of a smaller peak at 30 +/- 4 Ma. The results from short-lived radionuclides are compatible with an atmospheric pre-entry radius of 30-40 cm. However, based on noble gas and cosmogenic radionuclide data, Annama must have been part of a larger body (radius >65 cm) for a large part of its cosmic ray exposure history. The Be-10 concentration indicates a recent (3-5 Ma) breakup which may be responsible for the Annama parent body size reduction to 30-35 cm pre-entry radius.Peer reviewe

Noble gases, nitrogen and cosmic ray exposure age of the Sulagiri chondrite

AbstractThe Sulagiri meteorite fell in India on 12 September 2008, LL6 chondrite class is the largest among all the Indian meteorites. Isotopic compositions of noble gases (He, Ne, Ar, Kr and Xe) and nitrogen in the Sulagiri meteorite and cosmic ray exposure history are discussed. Low cosmogenic (22Ne/21Ne)c ratio is consistent with irradiation in a large body. Cosmogenic noble gases indicate that Sulagiri has a 4π cosmic-ray exposure (CRE) age of 27.9 ± 3.4 Ma and is a member of the peak of CRE age distribution of LL chondrites. Radiogenic 4He and 40Ar concentrations in Sulagiri yields the radiogenic ages as 2.29 and 4.56 Ga, indicating the loss of He from the meteorite. Xenon and krypton are mixture of Q and spallogenic components

Investigating noble gases and nitrogen in Zag (H3-6) and ALH 77216 (L3.7–3.9): The ordinary chondrites with solar type neon and argon

Concentrations and isotopic compositions of noble gases (He, Ne, Ar, Kr, and Xe) and nitrogen in two ordinary chondrites (OCs), Zag (H3-6) and ALH 77216 (L3.7–3.9), are presented. The aim of the study is to examine the cosmic ray exposure history, radiogenic ages and isotopic signatures of trapped gases in them. The results of stepwise heating analyses indicate that light noble gases (He and Ne) are mixture of trapped and cosmic ray produced components. Neon isotopes are enriched from solar wind (SW), while shows a trend towards galactic cosmic ray (GCR) region in both the meteorites. Phase-Q neon is not observed in any of the meteorite. The heavy noble gases Ar, Kr and Xe indicate mixture of Q-HL-SW and cosmogenic. Elemental ratios of trapped 36Ar, 84Kr and 132Xe indicate that noble gases in Zag and ALH 77216 are mixtures of the three components Q, HL and SW. The cosmic-ray exposure (CRE) ages calculated from neon for Zag and ALH 77216 are 5.6 ± 0.3 Ma and 28.5 ± 0.4 Ma, respectively. These ages are within the range typically observed for the respective meteorite types of OCs. Nitrogen isotopes indicate presence of multiple components in both the chondrites. Isotopic signature of trapped nitrogen in both the chondrites is distinct from that of SW, Q and HL, indicating additional source of nitrogen in the meteorites

Santa Lucia (2008) (L6) Chondrite, a Recent Fall: Composition, Noble Gases, Nitrogen and Cosmic Ray Exposure Age

International audienceThe Santa Lucia (2008)—one the most recent Argentine meteorite fall, fell in San Juan province, Argentina, on 23 January 2008. Several masses (total ~6 kg) were recovered. Most are totally covered by fusion crust. The exposed interior is of light-grey colour. Chemical data [olivine (Fa24.4) and low-Ca pyroxene (En77.8 Fs20.7 Wo1.6)] indicate that Santa Luica (2008) is a member of the low iron L chondrite group, corresponding to the equilibrated petrologic type 6. The meteorite name was approved by the Nomenclature Committee (NomCom) of the Meteoritical Society (Meteoritic Bulletin, no. 97). We report about the chemical composition of the major mineral phases, its bulk trace element abundance, its noble gas and nitrogen data. The cosmic ray exposure age based on cosmogenic 3He, 21Ne, and 38Ar around 20 Ma is comparable to one peak of L chondrites. The radiogenic K–Ar age of 2.96 Ga, while the young U, Th–He are of 1.2 Ga indicates that Santa Lucia (2008) lost radiogenic 4He more recently. Low cosmogenic (22Ne/21Ne)c and absence of solar wind noble gases are consistent with irradiation in a large body. Heavy noble gases (Ar/Kr/Xe) indicated trapped gases similar to ordinary chondrites. Krypton and neon indicates irradiation in large body, implying large pre-atmospheric meteoroid

Noble gases and nitrogen in the Almahata Sitta ureilite

A bulk sample (split from Almahata Sitta #36) and an acid resistant residue (from #44) have been analyzed for noble gases and nitrogen by step-wise combustion/pyrolysis. In the bulk sample, He and Ne are a mixture of cosmogenic and trapped components. Cosmic- ray exposure ages of 13.8 and 16.0 Ma are calculated based on 3He, and 21Ne, respectively. Except for a small amount of cosmogenic 3He, He, and Ne in the acid-resistant residue are not significantly above blank level. Ar, Kr, and Xe in both the bulk and residue are dominated by a trapped component, but the elemental ratios are different. While the ratios of 36Ar/132Xe and 84Kr/132Xe are about 400 and 1, respectively, in all the combustion steps of the residue, the bulk sample has about an order of magnitude more 132Xe in the corresponding combustion steps. It seems, an acid soluble phase is the host of this Xe-rich carrier and is different from a similar phase observed in the ureilite Allan Hills 82130. Nitrogen in the bulk sample and acid residue are 21.1 ppm (−36.8‰), and 249.5 ppm (−74.3‰), respectively. Peak release of C (monitored as CO + CO2), N, Ar, Kr, and Xe occurred at the 700 ° C combustion step of the residue, confirming diamond as the principal carrier for these gases. In the residue, the isotopic ratio 38Ar/36Ar shows a monotonic increase with release temperature