Ararki (L5) chondrite: The first meteorite find in Thar Desert of India
Ararki (L5) chondrite: The first meteorite find in Thar Desert of India
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Alarki (L5) 球粒陨石：印度塔尔沙漠发现的第一颗陨石
DOI：
10.1111/j.1945-5100.2008.tb00683.x
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发表时间：
2008
影响因子：
2.2
通讯作者：
I. Franchi
中科院分区：
文献类型：
--
作者：
N. Bhandari;S. Murty;P. N. Shukla;R. Mahajan;A. Shukla;G. Lashkari;M. S. Sisodia;R. Tripathi;G. Parthasarathy;H. C. Verma;I. Franchi
摘要：我们在这里报道了在印度西北部拉贾斯坦沙漠哈努曼加尔地区阿拉基村沙丘中偶然发现的陨石。化学和岩石学证据以及氧同位素组成表明它是 L5 球粒陨石。橄榄石中铁橄榄石含量为26.3mol%。该陨石含有一些蛇纹石化橄榄石和 0.3% 的碳，具有陆地同位素组成，表明它经历了中度风化。 22Na的缺失表明这颗陨石在十多年前坠落到地球上。基于宇宙成因 21Ne 的宇宙线暴露年龄为 7.2 Ma。宇宙线重核径迹密度低、26A1活度低、屏蔽参数[(22Ne/21Ne)C = 1.094]以及无中子俘获效应表明，半径约为16 cm的流星体存在宇宙线屏蔽，这意味着流星体质量约为60 kg，烧蚀程度约为93%。基于 U/Th-4He 和 K-40Ar 的气体保留年龄分别为 1.1 和 0.58 Ga，表明这颗陨石历史晚期发生过加热和脱气事件。
Abstract— 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 22Na indicate that the meteorite fell to Earth more than a decade ago. The cosmic‐ray exposure age based on cosmogenic 21Ne is 7.2 Ma. Low density of cosmic‐ray heavy nuclei tracks, low 26A1 activity, the shielding parameter [(22Ne/21Ne)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 on U/Th‐4He and K‐40Ar are 1.1 and 0.58 Ga, respectively, suggesting a heating and degassing event late in the history of this meteorite.