Abstract-A stony meteorite fell at Itawa Bhopji, Rajasthan, India on 2000 May 30. This is the fifth recorded fall in a small area of Rajasthan during the past decade. The meteorite is an ordinary chondrite with light clasts in a dark matrix, consisting of a mixture of equilibrated (mainly type 5) and unequilibrated components. Olivine is Fa24-26 and pyroxene FS 20-22 but, within the unequilibrated components, olivine (Fa5-29) and low calcium pyroxene (FS 5-37) are highly variable. Based on petrographic studies and chemical analyses, it is classified as L(3-5) regolith breccia. Studies of various cosmogenic records, including several gamma-emitting radionuclides varying in half-life from 5.6 day 52Mn to 0.73 Ma 26AI, tracks and rare gases have been carried out. The exposure age of the meteorite is estimated from cosmogenic components ofrare gases to be 19.6 Ma. The track density varies by a factor of -3 (from 4 to 12 x 10 6/cm2) within the meteorite, indicating a preatmospheric body of -9 ern radius (corresponding to a meteoroid mass of -11 kg) and small ablation (1.5 to 3.6 ern). Trapped components in various rare gases are high and the solar component is present in the dark portion of the meteorite. Large excess of neutron-produced 82Kr and 128Xe in both the light and the dark lithology but very low 60Co, indicating low neutron fluxes received by the meteoroid in the interplanetary space, are clear signatures of an additional irradiation on the parent body.

Abstract– 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.

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 chondri te. 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 smal ler peak at 30 ±4 Ma. The results from short-lived radionuclides are compatible with an atmosperic 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 10 Be 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.

A laser microprobe capable of analysing nitrogen and noble gases in individual grains with masses less than a milligram is described. It can be used in both continuous wave (CW) mode, useful for stepwise heating of an individual grain, as well as in pulsed mode, useful for ablating material from a small selected area of a sample, for gas extraction. We could achieve low blanks (in ccSTP units) for 4 He(4.8×10 −12), 22 Ne(1.0×10 −12), 36 Ar(1.0×10 −13), 84 Kr(2.9×10 −14), 132 Xe(2.6×10 −14), and N (87 pg), using this system. Preliminary data for individual chondrules from the Dhajala meteorite show that noble gases and nitrogen from grains as small as 170 microgram can be analysed using the present laser microprobe setup. The amount of trapped neon in Dhajala chondrules is very small, and nitrogen in the chondrules is isotopically heavier as compared to the bulk meteorite.

A single piece of meteorite fell on Kamargaon village in the state of Assam in India on November 13, 2015. Based on mineralogical, chemical, and oxygen isotope data, Kamargaon is classified as an L‐chondrite. Homogeneous olivine (Fa: 25 ± 0.7) and low‐Ca pyroxene (Fs: 21 ± 0.4) compositions with percent mean deviation of <2, further suggest that Kamargaon is a coarsely equilibrated, petrologic type 6 chondrite. Kamargaon is thermally metamorphosed with an estimated peak metamorphic temperature of ~800 °C as determined by two‐pyroxene thermometry. Shock metamorphism studies suggest that this meteorite include portions of different shock stages, e.g., S3 and S4 (Stöffler et al. ); however, local presence of quenched metal‐sulfide melt within shock veins/pockets suggest disequilibrium melting and relatively higher shock stage of up to S5 (Bennett and McSween ). Based on noble gas isotopes, the cosmic‐ray exposure age is estimated as 7.03 ± 1.60 Ma and nitrogen isotope composition (δ15N = 18‰) also correspond well with the L‐chondrite group. The He‐U, Th, and K‐Ar yield younger ages (170 ± 25 Ma 684 ± 93, respectively) and are discordant. A loss of He during the resetting event is implied by the lower He‐U and Th age. Elemental ratios of trapped Ar, Kr, and Xe can be explained through the presence of a normal Q noble gas component. Relatively low activity of 26Al (39 dpm/kg) and the absence of 60Co activity suggest a likely low shielding depth and envisage a small preatmospheric size of the meteoroid (<10 cm in radius). The Kr isotopic ratios (82Kr/84Kr) further argue that the meteorite was derived from a shallow depth.