干旱区生态环境知识资源中心

We report here a chance find of a meteorite in the sand dunes of Ararki village of Hanumangarh district in the Rajasthan desert of northwest India. Chemical and petrological evidence in conjunction with isotopic composition of oxygen indicate that it is an L5 chondrite. The fayalite content of olivines is 26.3 mol%. The meteorite has some serpentinized olivines and 0.3% carbon having a terrestrial isotopic composition, indicating that it is moderately weathered. The absence of Na-22 indicate that the meteorite fell to Earth more than a decade ago. The cosmic-ray exposure age based on cosmogenic Ne-21 is 7.2 Ma. Low density of cosmic-ray heavy nuclei tracks, low Al-26 activity, the shielding parameter [(Ne-22/Ne-21)(C) = 1.094] and absence of neutron capture effects indicate cosmic-ray shielding in a meteoroid having radius of about 16 cm, implying a meteoroid mass of about 60 kg and ablation of about 93%. The gas retention ages, based oil U/Th-He-4 and K-Ar-40 are 1.1 and 0.58 Ga, respectively, suggesting a heating and degassing event late in the history of this meteorite.