Shock‐thermal history of the Agoudal (IIAB) iron meteorite from microstructural studies

1D. Ray,1S. Ghosh,2H. Chennaoui Aoudjehane,3S. Das
Meteoritics & Planetary Science (in Prss) Link to Article [doi: 10.1111/maps.13399]
1Physical Research Laboralory, Ahrnedabad, Gujaral 380 009, lndia
2Facully of Sciences, GAIA Laboralory, Hassan 11 University Casablanca, llP 5366 Maarif, 20000, Casablanca, Morooco
3Department of Metallurgical and Materials Engineering, Indian lnsli_Lulc ofTcchnology’. Kharagpur 721302, lndia
Published by arrangement with John Wiley & Sons

The Agoudal IIAB iron meteorite exhibits only kamacite grains (~6 mm across)without any taenite. The kamacite is homogeneously enriched with numerous rhabditeinclusions of different size, shape, and composition. In some kamacite domains, this appearsfrosty due to micron-scale rhabdite inclusions (~5 to 100lm) of moderate to high Nicontent (~26 to 40 wt%). In addition, all the kamacite grains in matrix are marked with aprominent linear crack formed during an atmospheric break-up event and subsequentlyoxidized. This feature, also defined by trails of lowest Ni-bearing (mean Ni: 23 wt%) mm-scale rhabdite plates (fractured and oxidized) could be a trace of a pre-existingc–ainterface. Agoudal experienced a very slow rate of primary cooling~4°CMa1estimatedfrom the binary plots of true rhabdite width against corresponding Ni wt% and thecomputed cooling rate curves after Randich and Goldstein (1978). Chemically, Agoudaliron (Ga: 54 ppm; Ge: 140 ppm; Ir: 0.03 ppm) resembles the Ainsworth iron, the coarsestoctahedrite of the IIAB group. Agoudal contains multiple sets of Neumann bands that areformed in space and time at different scales and densities due to multiple impacts withshock magnitude up to 130 kb. Signatures of recrystallization due to postshock lowtemperature mild reheating at about 400°C are also locally present.

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