79th Annual Meeting of the Meteoritical Society (2016) sess701.pdf Thursday, August 11, 2016 EARLY SOLAR SYSTEM CHRONOLOGY I 8:30 a.m. Room B Chairs: Gregory Brennecka Audrey Bouvier 8:30 a.m. Kruijer T. S. * Kleine T. Tungsten Isotope Dichotomy Among Iron Meteorite Parent Bodies: Implications for the Timescales of Accretion and Core Formation [#6449] We report new combined Pt and W isotope data for IC, IIC, IIF, IIIE, and IIIF iron meteorites, with the ultimate aim of better understanding the variable pre-exposure 182W/184W signatures observed among different iron meteorite groups. 8:45 a.m. Tissot F. L. H. * Dauphas N. Grove T. L. Heterogeneity in the 238U/235U Ratios of Angrites [#6104] We report the 238U/235U ratios of six angrites. We find that the angrite-parent body was heterogeneous with regards to U isotopes. We correct the Pb-Pb ages of angrites and test their concordance with ages derived from short-lived chronometers. 9:00 a.m. Brennecka G. A. * Amelin Y. Kleine T. Combined 238U/235U and Pb Isotopics of Planetary Core Material: The Absolute Age of the IVA Iron Muonionalusta [#6296] We report a measured 238U/235U for the IVA iron Muonionalusta. This measured value requires an age correction of ~7 Myr to the previously published Pb-Pb age. This has major implications for our understanding of planetary core formation and cooling. 9:15 a.m. Cartwright J. A. * Amelin Y. Koefoed P. Wadhwa M. U-Pb Age of the Ungrouped Achondrite NWA 8486 [#6231] We report the U-Pb age for ungrouped achondrite NWA 8486 (paired with NWA 7325). Our improved isochron age of ~4564 Ma is similar to other ungrouped achondrites and angrites, suggesting that magmatic activity within ~4 Ma of CAI formation was common. 9:30 a.m. Dunlap D. R. * Romaniello S. J. Wadhwa M. 53Mn-53Cr Systematics of the Brachinite NWA 4882 [#6217] In this study, the 53Mn-53Cr systematics are presented for the Brachinite NWA 4882. These high precision results allow better understanding of the formation timeline and genetic relationship between the brachinite and other achondrite parent bodies. 9:45 a.m. Haba M. K. * Lai Y.-J. Yamaguchi A. Schönbächler M. Niobium-Zirconium Systematics of Meteoritic Rutiles: Application to the Chronology of Mesosiderites [#6139] Nb-Zr systematics of rutiles from mesosiderites was obtained using MC-ICPMS. Our data show an initial 92Nb/93Nb ratio of ~10–5 in the mesosiderite formation region and provide chronological constraint on the early evolution of the parent body. .