Meteoritics & Planetary Science 46, Nr 9, 1227–1252 (2011) doi: 10.1111/j.1945-5100.2011.01210.x Thermal and impact histories of reheated group IVA, IVB, and ungrouped iron meteorites and their parent asteroids J. YANG1,2*, J. I. GOLDSTEIN1, E. R. D. SCOTT3, J. R. MICHAEL4, P. G. KOTULA4, T. PHAM1, 5 and T. J. MCCOY 1Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, Massachusetts 01003, USA 2Carl Zeiss NTS, LLC, One Corporation Way, Peabody, Massachusetts 01960, USA 3Hawaii Institute of Geophysics and Planetology, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA 4Materials Characterization Department, Sandia National Laboratories, P.O. Box 5800, MS 0886, Albuquerque, New Mexico 87185, USA 5Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia 20560, USA *Corresponding author. E-mail:
[email protected] (Received 20 December 2010; revision accepted 21 April 2011) Abstract–The microstructures of six reheated iron meteoriteso¨ two IVA irons, Maria Elena (1935), Fuzzy Creek; one IVB iron, Ternera; and three ungrouped irons, Hammond, Babb’s Mill (Blake’s Iron), and Babb’s Mill (Troost’s Iron)o¨ were characterized using scanning and transmission electron microscopy, electron-probe microanalysis, and electron backscatter diffraction techniques to determine their thermal and shock history and that of their parent asteroids. Maria Elena and Hammond were heated below approximately 700–750 °C, so that kamacite was recrystallized and taenite was exsolved in kamacite and was spheroidized in plessite. Both meteorites retained a record of the original WidmanstI` tten pattern. The other four, which show no trace of their original microstructure, were heated above 600–700 °C and recrystallized to form 10–20 lm wide homogeneous taenite grains.