¹S. N. Teplyakova,²M. Humayun,¹C. A. Lorenz,¹M. A. Ivanova
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13898]
¹Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygina st. 19, 119991 Moscow, Russia
²National High Magnetic Field Laboratory and Department of Earth, Ocean & Atmospheric Science, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, Florida, 32310 USA
Published by arrangement with John Wiley & Sons

Isotopic compositions of O, Mo, and Cu in the IIE iron meteorites have indicated a close affinity to the H chondrite group. The diversity of trace element compositions and their abundance of silicate inclusions indicate that IIE iron meteorites were formed in multistage processes. To better constrain the formation of the IIE irons, this study analyzed elemental abundances in the metal of five IIE irons (Elga, Miles, Tobychan, Verkhne Dnieprovsk, and Watson) by laser ablation inductively coupled plasma mass spectrometry. The data are interpreted in terms of a new model of IIE crystallization from the metal fraction of completely molten H chondrite-like material based on the solid/liquid distribution coefficients of siderophile and chalcophile elements changing simultaneously with changes of S concentrations in the remaining liquid during the crystallization of the Fe,Ni phase in the Fe-Ni-S system. The model showed that IIE iron compositions could be produced as solid phases at 40–73 wt% of fractional crystallization of the metal component of a bulk H chondrite-like metallic melt. We propose that IIE iron metal could have originated from the solidified core of a differentiated body of H chondrite-like composition and sampled different fractions of that core exposed during a catastrophic disruption of the body. The present structure of metal and silicate inclusions of IIE irons was formed by remelting and metal–silicate mixing during late impact event(s) on the parent body surface.

¹A. Dixit,²R. P. Tripathi,³Sudhanshu Kumar,³Mohd. Azaj Ansari,³K. Sreenivas
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13888]
¹Department of Physics, Indian Institute of Technology, Jodhpur, 342037 India
²78, BGKT Extension Scheme, New Pali Road, Jodhpur, 342005 India
³Department of Physics and Astrophysics, University of Delhi, Delhi, 110007 India
Published by arrangement with John Wiley & Sons

Fourier transform infrared (FTIR) measurements on immediately collected Mukundpura show the typical feature for phyllosilicates around 10 μm, corresponding to Si-O stretching mode in silicate, and its broadness signifies the amorphous or poorly crystalline silicates. The absence of the 11.2 μm feature (a characteristic of anhydrous silicate olivine) and the weight loss observed in thermogravimetric analysis (TGA) imply aggressive aqueous alteration, which resulted in phyllosilicate formation at the expense of primary anhydrous silicates. It is consistent with Mössbauer spectra, showing the presence of both Fe2+ and Fe3+ in phyllosilicates, but no characteristic peak for olivine is observed, suggesting the major fraction of primary silicates are aggressively altered due to the presence of water on the parent body, and now major lithology must be highly altered. TGA measurements were carried on it (i) within 24 h and (ii) after 30 months of its fall. In both cases, the weight loss was ∼10% in the 400–770 °C temperature range, confirming the absence of any environmental impact on the water bound to the hydrated clay in Mukundpura samples. Appreciable weight loss in 400–770 °C indicated the presence of hydrated clay that corroborated FTIR measurements and ruled out any thermal event suffered by its postaqueous alteration, consistent with amorphous or poorly crystalline silicate phase observed in FTIR. When we couple the results of the present study and already reported results by our group on the same Mukundpura fragment, it is inferred that our sample has suffered a very high degree of aqueous alteration on the parent body. The fingerprint ratios, which are extensively used to correlate or assign petrological subgroup, are FeO/SiO2, hydrous silicate/anhydrous silicates, and MgO/FeO, which are either considered alone or in combination, and for Mukundpura, the values for these ratios are 1.05, 7.2, and ∼0.60, respectively. These values indicate that the major lithology of Mukundpura fresh fragment must be assigned as CM2.1.