gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1998.62A.3.12 Longevity of Cratonic Mantle Beneath an Active Rift: Re-Os Evidence from Xenoliths from the Tanzanian East African Rift Rudnick R. L. Dept. of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA Chesley J. T. Dept. of Geological Sciences, University of Arizona, Tucson, AZ 85721, USA Lee C.-T. Dept. of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA 1998 62A 3 1297 1298 Copyright © 1998, The Mineralogical Society 1998