gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1994.58A.2.105 Re-Os Isotope Evidence for a Mid-Archaean Age of Diamondiferous Eclogite Xenoliths from the Udachnaya Kimberlite, Siberia: Constraints on Eclogite Petrogenesis. and Archaean Tectonics Pearson D. G. Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, UK Shirey S. B. Department of Terrestrial Magnetism, 5241 Broad Branch Rd, N.W. Washington, D.C. 20015, USA Sobolev N. V. Institute of Mineralogy and Petrography, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia Snyder G. A. Taylor L. A. Department of Geological Sciences, University of Tennessee, Knoxville, TN 37996, USA August–September 1994 58A 2 705 706 Copyright © 1994, The Mineralogical Society 1994